Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

1

Self-Study Modules 

on Tuberculosis

Targeted Testing and 

the Diagnosis of 

Latent Tuberculosis 

Infection and 

Tuberculosis Disease Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 2

Module 3: Objectives

At completion of this module, learners will be able to:

1. Identify high-risk groups for targeted testing

2. Describe how to place, read, and interpret a

Mantoux tuberculin skin test (TST)

3. Describe how to interpret an interferongamma release assay (IGRA)

4. Discuss considerations for using either the 

TST or IGRA for diagnosing latent 

tuberculosis infection (LTBI)

5. Describe the components of a medical 

evaluation for diagnosing TB disease

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 3

Module 3: Overview

• Targeted Testing

• Diagnosis of latent tuberculosis infection (LTBI)

– TST

– IGRAs

– TB Testing Programs, the Booster 

Phenomenon, and Two-Step Testing

• Diagnosis of TB Disease

• Reporting TB Cases

• Case Studies

4

Targeted Testing

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 5

Targeted Testing (1)

• Targeted testing is a TB control strategy 

used to identify and treat persons:

– At high risk for latent TB infection (LTBI)

– At high risk for developing TB disease 

once infected with M. tuberculosis

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 6

• Identifying persons with LTBI is an important 

goal of TB elimination because LTBI 

treatment can:

– Prevent the development of TB disease

– Stop the further spread of TB to others

Targeted Testing (2)
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

2

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 7

Targeted Testing (3)

A Decision to Test is a Decision to Treat

• TB testing activities should be done only when 

there is a plan for follow-up care

• Health care workers (HCWs) should identify and 

test persons who are at high risk

– People who are not at high risk generally 

should not be tested

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 8

Targeted Testing (4)

High-Risk Groups 

• High-risk groups can be divided into two 

categories:

– People who are at high risk for exposure to or 

infection with M. tuberculosis

– People who are at high risk for developing TB 

disease once infected with M. tuberculosis

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 9

Targeted Testing (5)

High-Risk Groups for TB Infection

• Contacts of people known or suspected to 

have TB disease

• People who have come to U.S. within 5 years 

from areas of the world where TB is common

• People who visit areas with a high prevalence 

of TB disease

• People who live or work in high-risk 

congregate settings

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 10

• HCWs who serve patients at increased risk 

for TB disease

• Populations defined locally as having an 

increased incidence of LTBI or TB disease 

(e.g., medically underserved, low income, or 

people who abuse drugs or alcohol)

• Infants, children, and adolescents exposed 

to adults in high-risk groups

Targeted Testing (6)

High-Risk Groups for TB Infection

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 11

• People living with HIV 

• Children younger than 5 years of age

• People recently infected with M. tuberculosis 

(within the past 2 years)

• People with a history of untreated or inadequately 

treated TB disease

• People receiving immunosuppressive therapy

Targeted Testing (7)

High-Risk Groups for TB Disease after 

Infection with M. tuberculosis

Targeted Testing (8)

High-Risk Groups for TB Disease after 

Infection with M. tuberculosis

• Persons with silicosis, diabetes mellitus, chronic renal 

failure, leukemia, or cancer of the head, neck, or lung

• Persons who have had a gastrectomy or jejunoileal 

bypass

• Low body weight

• Cigarette smokers and persons who abuse drugs and 

alcohol

• Persons defined locally as having an increased incidence 

of disease due to M. tuberculosis

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 12
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

3

13

Diagnosis of Latent TB 

Infection (LTBI)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 14

Diagnosis of LTBI

• Available testing methods for M. tuberculosis

infection:

– Mantoux tuberculin skin test (TST)

– Blood tests known as interferon-gamma 

release assays (IGRAs):

• QuantiFERON®-TB Gold In-Tube (QFT-GIT)

• T-SPOT®.TB test (T-Spot)

15

Diagnosis of Latent TB 

Infection (LTBI)

Mantoux Tuberculin Skin Test

Administering the Test

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 16

Mantoux Tuberculin Skin Test (1)

• TST is administered by 

injection

• Tuberculin is made from 

proteins derived from 

inactive tubercle bacilli

• Most people who have TB 

infection will have a 

reaction at injection site Syringe being filled with 0.1 ml of liquid 

tuberculin

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 17

0.1 ml of 5 tuberculin units of liquid tuberculin are 

injected between the layers of skin on forearm

Mantoux Tuberculin Skin Test (2)

HCW administering Mantoux TST

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 18

Mantoux Tuberculin Skin Test (3)

• Forearm should be 

examined within 48 to 72 

hours by HCW

• Reaction is an area of 

induration (swelling) 

around injection site

– Induration is measured 

in millimeters

– Erythema (redness) is 

not measured Only the induration is measured
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

4

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 19

Mantoux Tuberculin Skin Test 

Study Question 3.1

What is the TST used for? 

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 20

Mantoux Tuberculin Skin Test 

Study Question 3.2

How is the TST given? 

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 21

With the TST, when is the patient’s arm 

examined? 

Mantoux Tuberculin Skin Test 

Study Question 3.3

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 22

Mantoux Tuberculin Skin Test 

Study Question 3.4

How is the induration measured? 

23

Diagnosis of Latent TB 

Infection (LTBI)

Mantoux Tuberculin Skin Test

Interpreting the Reaction

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 24

Interpretation of TST reaction depends on size of 

induration and person’s risk factors for TB

Mantoux Tuberculin Skin Test (4)

Interpreting the Reaction
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

5

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 25

• Induration of > 5 mm is considered positive for: 

– People living with HIV

– Recent contacts of people with infectious TB

– People with chest x-ray findings suggestive 

of previous TB disease

– People with organ transplants

– Other immunosuppressed patients

Mantoux Tuberculin Skin Test (5)

Interpreting the Reaction

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 26

Mantoux Tuberculin Skin Test (6)

Interpreting the Reaction

• Induration of > 10 mm is considered a positive 

reaction for: 

– People who have recently come to U.S. from 

areas where TB is common

– People who abuse drugs

– Mycobacteriology laboratory workers

– People who live or work in high-risk 

congregate settings

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 27

• Induration of > 10 mm is considered a 

positive reaction for: 

– People with certain medical conditions that 

increase risk for TB (e.g., silicosis, diabetes 

mellitus, severe kidney disease, certain 

types of cancer, and certain intestinal 

conditions)

– Children younger than 5 years of age

– Infants, children, or adolescents exposed to 

adults in high-risk categories

Mantoux Tuberculin Skin Test (7)

Interpreting the Reaction

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 28

• Induration of > 15 mm is considered a 

positive reaction for people who have no 

known risk factors for TB

Mantoux Tuberculin Skin Test (8)

Interpreting the Reaction

Occupational Exposure

• For people who may be exposed to TB 

on the job (e.g., HCWs, staff of nursing 

homes or correctional facilities), 

interpretation of TST depends on:

– The employee’s individual risk factors for 

TB

– The risk of exposure to TB in the person’s 

job

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 29 Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection and Tuberculosis Disease 30

Mantoux Tuberculin Skin Test 

Study Question 3.5

What two factors determine the interpretation 

of a skin test reaction as positive or 

negative? What additional factor is 

considered for people who may be exposed 

to TB on the job?
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

6

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 31

Name 5 groups of people for which > 5 mm of 

induration is considered a positive reaction? 

Mantoux Tuberculin Skin Test 

Study Question 3.6

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 32

Mantoux Tuberculin Skin Test 

Study Question 3.7

Name seven groups of people for which > 10 mm 

of induration is considered a positive reaction.

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 33

For which group of people is > 15 mm of 

induration considered a positive reaction?

Mantoux Tuberculin Skin Test 

Study Question 3.8

34

Diagnosis of Latent TB 

Infection (LTBI)

Mantoux Tuberculin Skin Test

Factors that Affect the Reaction

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 35

• Factors that may cause people to have a 

positive reaction even if they do not have TB 

infection:

– Infection with nontuberculous 

mycobacteria (NTM)

– BCG vaccination

– Administration of incorrect antigen

– Incorrect measuring or interpretation of 

TST reaction

Mantoux Tuberculin Skin Test (9)

False-Positive Reaction

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 36

• People who have been vaccinated with BCG 

may have a false-positive TST reaction

– However, there is no reliable way to 

distinguish a positive TST reaction caused by 

BCG vaccination from a reaction caused by 

true TB infection

• Individuals should always be further evaluated 

if they have a positive TST reaction

Mantoux Tuberculin Skin Test (10)

BCG Vaccine
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

7

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 37

• Factors that may cause false-negative 

reactions:

– Anergy

– Recent TB infection (within past 8 to 10 weeks)

• It can take 2 to 8 weeks after TB infection for 

body’s immune system to react to tuberculin

– Very young age (younger than 6 months)

– Recent live-virus measles or smallpox vaccination

– Incorrect method of giving the TST

– Incorrect measuring or interpretation of TST reaction

Mantoux Tuberculin Skin Test (11)

False-Negative Reaction

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 38

• Inability to react to skin tests due to 

weakened immune system

• Anergy testing is no longer routinely 

recommended

Mantoux Tuberculin Skin Test (12)

Anergy

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 39

Mantoux Tuberculin Skin Test (13)

Any patient with symptoms of TB disease

should be evaluated for TB disease, regardless 

of his or her skin test reaction.

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 40

Name four factors that may cause false-positive 

reactions to the TST.

Mantoux Tuberculin Skin Test 

Study Question 3.9

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 41

Is there a reliable way to distinguish a 

positive TST reaction caused by vaccination 

with BCG from a reaction caused by true TB 

infection?

Mantoux Tuberculin Skin Test 

Study Question 3.10

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 42

Name 6 factors that may cause false-negative 

reactions to the TST.

Mantoux Tuberculin Skin Test 

Study Question 3.11
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

8

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 43

Mantoux Tuberculin Skin Test 

Study Question 3.12

What is anergy?

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 44

After TB germs have been transmitted to 

someone, how long does it take before TB 

infection can be detected by the TST?

Mantoux Tuberculin Skin Test 

Study Question 3.13

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 45

Mantoux Tuberculin Skin Test 

Study Question 3.14

What should be done if a patient has a 

negative TST result, but has symptoms of TB 

disease?

46

Diagnosis of Latent TB 

Infection (LTBI)

Interferon-Gamma 

Release Assays (IGRAs)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 47

Types of IGRAs

• QuantiFERON®-TB Gold 

In-Tube (QFT-GIT)

– Approved in 2007

• T-Spot®.TB test (T-SPOT)

– Type of ELISpot assay

– Approved in 2008

• CDC guidelines for 

IGRAs published in 2010

T-Spot®.TB testing materials

QFT-GIT testing materials

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 48

• Blood tests that help diagnose M. tuberculosis

infection

• Measures a person’s immune reactivity to 

M. tuberculosis

IGRAs (1)
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

9

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 49

IGRAs (2)

Conducting the Test

• Confirm arrangements for testing in a qualified 

laboratory

• Arrange for delivery of the blood sample to the 

laboratory in the time the laboratory specifies

• Draw a blood sample from the patient according to 

the manufacturer’s instructions

• Schedule follow-up appointment for patient to 

receive test results

• Based on test results, provide follow-up evaluation

and treatment as needed 

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 50

• Blood samples are mixed with antigens (protein 

substances that can produce an immune 

response) and incubated

• If the person is infected with M. tuberculosis,

blood cells will recognize antigens and release 

interferon gamma (IFN-γ) in response

IGRAs (3)

How it Works

IGRAs (4)

Interpreting Results

• QFT-GIT Results

– Based on amount of IFN-γ released in 

response to M. tuberculosis antigens and 

control substances

• T-Spot Results

– Based on number of IFN-γ producing cells 

(spots) produced

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 51 Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection and Tuberculosis Disease 52

IGRAs (5)

Interpreting Results

• Qualitative test 

interpretation and 

quantitative assay 

measurements should be 

reported

• Laboratories use software 

provided by manufacturer 

to calculate results QFT-GIT Results

• Results are sent to requesting 

health care provider

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 53

IGRAs (6)

Report of Results

IGRA Result Interpretation

Positive M. tuberculosis infection likely

Negative M. tuberculosis infection unlikely, but cannot be 

excluded especially if

1. Patient has signs and symptoms of TB 

2. Patient has a high risk for developing TB 

disease once infected with M. tuberculosis 

Indeterminate The test did not provide useful information about 

the likelihood of M. tuberculosis infection. 

Repeating an IGRA or performing a TST may be 

useful. 

Borderline 

(T-Spot only)

The test did not provide useful information about 

the likelihood of M. tuberculosis infection. 

Repeating an IGRA or performing a TST may be 

useful.

IGRA Recommendations (1)

• IGRAs are the preferred method of testing in

– Groups of people who might be less likely 

to return for TST reading and interpretation 

– Persons who have received the BCG 

vaccine

• TST is the preferred method of testing for 

children younger than 5 years of age

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 54
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

10

• Routine testing using both TST and IGRAs is NOT 

recommended

• Certain situations where results from both tests may 

be useful:

– When the initial test is negative and: 

• Risk for infection, progression to disease, or a 

poor outcome is high 

• There is clinical suspicion for TB disease and 

confirmation of M. tuberculosis infection is 

desired

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 55

IGRA Recommendations (2)

• Certain situations where results from both tests 

may be useful

– When the initial test is positive and:

• Additional evidence of infection is required 

to encourage the patient’s acceptance and 

adherence to treatment

• Person has a low risk of both infection and 

progression from infection to TB disease 

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 56

IGRA Recommendations (3)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 57

• Requires single patient visit to conduct test

• Results can be available in 24 hours

• Does not cause booster phenomenon which 

can happen with repeat TSTs

• BCG vaccination does not affect IGRA results

IGRA Advantages

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 58

• Blood samples must be processed within 8 to 

30 hours after collection

• Errors in collecting or transporting blood 

specimens or in running and interpreting test 

can decrease accuracy 

• Limited data on its use in certain populations 

(e.g., children younger than 5, persons 

recently infected, immunocompromised 

persons, and serial testing)

IGRA Disadvantages and 

Limitations (1)

IGRA Disadvantages and 

Limitations (2)

• Limited data on its use to predict who 

will progress to TB disease

• Tests may be expensive

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 59 Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection and Tuberculosis Disease 60

What are the steps for conducting an IGRA?

IGRAs

Study Question 3.15
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

11

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 61

How are IGRA results interpreted?

IGRAs

Study Question 3.16

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 62

IGRAs

Study Question 3.17

How should negative IGRA results be

interpreted? 

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 63

What are 5 advantages for using an IGRA as

compared to the TST?

IGRAs

Study Question 3.18

64

Diagnosis of Latent TB 

Infection (LTBI)

TB Testing Programs, the Booster 

Phenomenon, and Two-Step Testing

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 65

• Many residential facilities, health care settings, 

and other settings have TB testing programs

– Employees and residents are periodically 

given TSTs or IGRAs

• Testing programs: 

– Identify people who have LTBI or TB disease 

so they can be given treatment as needed

– Determine whether TB is being transmitted in 

facility

TB Testing Programs (1)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 66

• Employees or residents are given TSTs or 

IGRAs when they first enter facility

– If person is negative, they may be retested 

at regular intervals thereafter

TB Testing Programs (2)

Baseline Test
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

12

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 67

TB Testing Programs (3)

Conversion

• Persons whose TST or IGRA result converts 

from negative to positive may have been 

infected with M. tuberculosis

– TST or IGRA conversions may indicate 

that TB is being transmitted in facility

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 68

• Phenomenon in which people who are skin tested 

many years after they became infected with TB have:

– Negative reaction to initial TST

– Positive reaction to subsequent TST given up to 

one year later

• Occurs mainly in older adults

• May affect accuracy of baseline skin test 

• TST can boost subsequent IGRA results

Booster Phenomenon

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 69

Person is skin tested years later

Person is skin tested again, up 

to 1 year later. For this 

example, we assume that the 

person was NOT exposed to 

TB during this time

Person has a positive reaction. This 

is a boosted reaction due to TB 

infection that occurred a long time 

ago, not during the time between the 

two skin tests

Occurs mainly in 

previously infected, 

older adults whose 

ability to react to 

tuberculin has 

decreased over time

Figure 3.6 

The booster phenomenon with the TST

Person becomes infected with M. tuberculosis

As years pass, 

person’s ability to 

react to tuberculin 

lessens

Person has negative reaction due to 

lessened ability to react to tuberculin

However, this skin test “jogs the 

memory” of the immune system to 

recognize and react to tuberculin

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 70

• Only conducted when TST is used

• Distinguishes between boosted reactions and reactions 

caused by recent infections

• Should be used for initial skin testing of persons who will 

be retested periodically

• If person’s initial skin test is negative, they should be 

given a second test 1 to 3 weeks later

– Second test positive: probably boosted reaction

– Second test negative: considered uninfected

Two-Step Testing

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 71

Baseline skin test

Reaction

Negative Positive

Reaction

Negative Positive

Retest 1-3 weeks later Person probably has TB infection

Person probably 

does NOT have 

TB infection

Reaction is considered 

a boosted reaction 

(due to TB infection 

that occurred a long 

Repeat at regular time ago)

intervals; a positive 

reaction will probably 

be due to a recent TB 

infection

Retesting not 

necessary

Figure 3.7 

Two-step testing with the TST

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 72

What is the booster phenomenon?

Booster Phenomenon

Study Question 3.19
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

13

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 73

What is the purpose of two-step testing?

Two-Step Testing

Study Question 3.20

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 74

Two-Step Testing

Study Question 3.21

In what type of situation is two-step testing 

used?

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 75

How is two-step testing done?

Two-Step Testing

Study Question 3.22

76

Diagnosis of TB Disease

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 77

• Anyone with TB symptoms or positive TST or 

IGRA result should be medically evaluated for 

TB disease

• Components of medical evaluation:

1. Medical history

2. Physical examination

3. Test for TB infection

4. Chest x-ray

5. Bacteriological examination

Medical Evaluation

78

1. Medical History

2. Physical Examination

3. Test for TB Infection

Diagnosis of TB Disease

Medical Evaluation
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

14

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 79

1. Medical History (1)

• Clinicians should ask patients if they have:

– Symptoms of TB disease

– Been exposed to a person with infectious TB 

or have risk factors for exposure to TB 

– Any risk factors for developing TB disease

– Had LTBI or TB disease before

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 80

1. Medical History (2)

General Symptoms of TB Disease

• Fever 

• Chills

• Night sweats

• Weight loss

• Appetite loss

• Fatigue

• Malaise

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 81

• Cough lasting 3 or more weeks

• Chest pain 

• Coughing up sputum or blood

1. Medical History (3)

Symptoms of Pulmonary TB Disease

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 82

• Symptoms of extrapulmonary TB disease 

depend on part of body that is affected

• For example:

– TB disease in spine may cause back pain

– TB disease in kidneys may cause blood in 

urine

1. Medical History (4)

Symptoms of Extrapulmonary TB Disease

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 83

A physical examination cannot confirm or rule out 

TB disease, but can provide valuable information

2. Physical Examination

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 84

3. Test for TB Infection (1)

• Types of tests available 

for diagnosing TB 

infection in U.S.:

– Mantoux TST

– IGRAs

• QFT-GIT

• T-SPOT
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

15

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 85

3. Test for TB Infection (2)

• Patients with symptoms of TB disease 

should always be evaluated for TB disease, 

regardless of their TST or IGRA test result

– Clinicians should not wait for TST or IGRA 

results before starting other diagnostic 

tests

– TST or IGRA should be given at the same 

time as other steps in the diagnosis of TB 

disease

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 86

What are the 5 components for conducting a 

medical evaluation for diagnosing TB disease?

Diagnosis of TB Disease

Study Question 3.23

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 87

What parts of a patient’s medical history should 

lead a clinician to suspect TB?

Diagnosis of TB Disease

Study Question 3.24

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 88

What are the symptoms of pulmonary TB 

disease? What are the symptoms of 

extrapulmonary TB disease?

Diagnosis of TB Disease 

Study Question 3.25

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 89

For patients with symptoms of TB disease, 

should clinicians wait for TST or IGRA 

results before starting other diagnostic 

tests?

Diagnosis of TB Disease 

Study Question 3.26

90

Diagnosis of TB Disease

Medical Evaluation

4. Chest X-Ray
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

16

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 91

• When a person has TB 

disease in the lungs, the 

chest x-ray usually 

appears abnormal. It 

may show:

– Infiltrates (collections 

of fluid and cells in 

lung tissue)

– Cavities (hollow 

spaces within the 

lung)

4. Chest X-Ray (1)

Abnormal chest x-ray with cavity

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 92

• Chest x-rays can:

– Help rule out possibility of pulmonary TB 

disease in persons who have a positive TST 

or IGRA result

– Check for lung abnormalities 

4. Chest X-Ray (2)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 93

4. Chest X-Ray (3)

• Chest x-rays cannot confirm TB disease

– Other diseases can cause lung 

abnormalities

– Only bacteriologic culture can confirm 

patient has TB disease

– Chest x-ray may appear unusual or even 

appear normal for persons living with HIV

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 94

Name 2 purposes of the chest x-ray. 

Chest X-Ray

Study Question 3.27

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 95

Chest X-Ray

Study Question 3.28

Can the results of a chest x-ray confirm that 

a person has TB disease? Why or why not?

96

Diagnosis of TB Disease

Medical Evaluation

5. Bacteriologic 

Examination
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

17

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 97

5. Bacteriologic Examination (1)

• TB bacteriologic examination is done in a 

laboratory that specifically deals with M. 

tuberculosis and other mycobacteria

– Clinical specimens (e.g., sputum, urine) 

are examined and cultured in laboratory

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 98

• Bacteriologic examination has 5 parts

– Specimen collection

– Examination of acid-fast bacilli (AFB) 

smears

– Direct identification of specimen (nucleic 

acid amplification)

– Specimen culturing and identification

– Drug susceptibility testing

5. Bacteriologic Examination (2)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 99

5. Bacteriologic Examination (3)

Specimen Collection

• For pulmonary TB, 

specimens can be 

collected by:

– Coughing up sputum 

sample

– Inducing sputum 

sample

– Bronchoscopy

– Gastric washing

TB patient coughing up sputum in a sputum collection booth

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 100

• Easiest and least expensive method is to 

have patient cough into sterile container 

• HCWs should coach and instruct patient

• Should have at least 3 sputum specimens 

examined

– Collected in 8 to 24 hour intervals

– At least one early morning specimen

5. Bacteriologic Examination (4) 

Sputum Sample Specimen Collection

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 101

5. Bacteriologic Examination (5) 

Induced Sputum Collection

• Induced sputum collection should be used if 

patient cannot cough up sputum on their 

own

• Patient inhales saline mist, causing deep 

coughing

• Specimen often clear and watery, should be 

labeled “induced specimen”

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 102

5. Bacteriologic Examination (6)

Bronchoscopy

• Bronchoscopy may be used:

– If patient cannot cough up 

enough sputum

– If an induced sputum cannot 

be obtained

• Procedure: instrument is 

passed through the mouth into 

the diseased portion of the 

lung to obtain sputum or lung 

tissue

Bronchoscopy being performed on a patient
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

18

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 103

5. Bacteriologic Examination (7)

Gastric Washing

• Usually only used if sample cannot be 

obtained from other procedures

• Often used with children 

• Tube is inserted through nose and into 

stomach to obtain gastric secretions that 

may contain sputum 

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 104

• Specimens other than sputum may be obtained

• Depends on part of body affected

• For example:

– Urine samples for TB disease of kidneys

– Fluid samples from area around spine for TB 

meningitis

5. Bacteriologic Examination (8) 

Extrapulmonary TB

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 105

5. Bacteriologic Examination (9)

Examination of AFB Smears

• Specimens are 

smeared onto glass 

slide and stained

• AFB are 

mycobacteria that 

remain stained after 

being washed in 

acid solution 

AFB smear

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 106

• Number of AFB on smear are counted

• According to number of AFB seen, smears are 

classified as 4+, 3+, 2+, or 1+

– For example, 4+ smear has 10 times as many AFB 

than 3+ smear

• If very few AFB are seen, the smear is classified by 

the actual number of AFB seen

• A negative smear does not rule out the possibility of 

TB 

5. Bacteriologic Examination (10)

Examination of AFB Smears

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 107

5. Bacteriologic Examination (11)

Examination of AFB Smears

Classification 

of Smear Smear Result Infectiousness of Patient

4+ Strongly positive Probably very

infectious

3+ Strongly positive Probably very

infectious

2+ Moderately positive Probably infectious

1+ Moderately positive Probably infectious

Actual number 

of AFB seen 

(no plus sign)

Weakly positive Probably infectious

No AFB seen Negative May not be

infectious

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 108

What are the 4 ways to collect sputum 

specimens? Indicate which procedure is the 

least expensive and easiest to perform.

Bacteriologic Examination

Study Questions 3.29
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

19

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 109

What do laboratory personnel look for in a 

smear?

Bacteriologic Examination

Study Question 3.30

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 110

Bacteriologic Examination

Study Question 3.31

What does a positive smear indicate about a 

patient’s infectiousness?

111

Diagnosis of TB Disease

Medical Evaluation

5. Bacteriologic 

Examination (continued)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 112

5. Bacteriologic Examination (12)

Nucleic Acid Amplification Tests (NAA)

• NAA tests directly identify M. tuberculosis

from sputum specimens by:

– Amplifying (copying) DNA and RNA 

segments

• Can help guide clinician’s decision for 

patient therapy and isolation

• Does not replace need for AFB smear, 

culture, or clinical judgment

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 113

5. Bacteriologic Examination (13)

Nucleic Acid Amplification Tests (NAA)

• If NAA test and AFB smears are positive:

– Patient is presumed to have TB and should 

begin treatment 

• If NAA test is negative and AFB smears are 

positive:

– Patient may have nontuberculous 

mycobacteria infection (NTM)

5. Bacteriologic Examination (14)

Xpert MTB/RIF Assay

• Xpert MTB/RIF assay is a NAA test that 

simultaneously detects Mycobacterium 

tuberculosis complex (MTBC) and resistance to 

rifampin

• To conduct this test, a sputum sample is mixed 

with the reagent that is provided with the assay

• A cartridge containing the mixture is placed in 

the GeneXpert machine

• Results are available in less than 2 hours

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 114
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

20

5. Bacteriologic Examination (15)

Xpert MTB/RIF Assay

• Results that are positive for MTBC and for rifampin

resistance indicate that the bacteria have a high 

probability of resistance to rifampin

– Should be confirmed by additional rapid testing

• If rifampin resistance is confirmed, rapid molecular 

testing for drug resistance to both first-line and 

second-line drugs should be performed so an 

effective treatment regimen can be selected

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 115 Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection and Tuberculosis Disease 116

5. Bacteriologic Examination (16)

Culturing and Identifying Specimen

• Culturing:

– Determines if 

specimen contains 

M. tuberculosis 

– Confirms diagnosis 

of TB disease

• All specimens should 

be cultured

Colonies of M. tuberculosis growing on media

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 117

5. Bacteriologic Examination (17)

Culturing and Identifying Specimen

• Step 1: Detect growth of mycobacteria

– Solid media: 3 to 6 weeks

– Liquid media: 4 to 14 days

• Step 2: Identify organism that has grown

– Nucleic acid probes: 2 to 4 hours

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 118

• Positive culture: M. tuberculosis identified in 

patient’s culture

– Called M. tuberculosis isolate

– Confirms diagnosis of TB disease

5. Bacteriologic Examination (18)

Culturing and Identifying Specimen

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 119

5. Bacteriologic Examination (19)

Culturing and Identifying Specimen

• Negative culture: M. tuberculosis NOT 

identified in patient’s culture

– Does not rule out TB disease

– Some patients with negative cultures are 

diagnosed with TB based on signs and 

symptoms

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 120

• Bacteriological examinations are important 

for assessing infectiousness and response 

to treatment

• Specimens should be obtained monthly until 

2 consecutive cultures are negative

• Culture conversion is the most important 

objective measure of response to treatment

5. Bacteriologic Examination (20)

Culturing and Identifying Specimen
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

21

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 121

• Conducted when patient is first found to 

have positive culture for TB

• Determines which drugs kill tubercle bacilli

• Tubercle bacilli killed by a particular drug are 

susceptible to that drug

• Tubercle bacilli that grow in presence of a 

particular drug are resistant to that drug

5. Bacteriologic Examination (21)

Drug Susceptibility Testing

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 122

5. Bacteriologic Examination (22)

Drug Susceptibility Testing

• Tests should be 

repeated if:

– Patient has 

positive culture 

after 3 months of 

treatment; or 

– Patient does not 

get better

Drug susceptibility testing on solid media

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 123

5. Bacteriologic Examination (23)

Types of Drug-Resistant TB

Mono-resistant Resistant to any one TB treatment 

drug

Poly-resistant Resistant to at least any two TB drugs 

(but not both isoniazid and rifampin)

Multidrugresistant 

(MDR TB)

Resistant to at least isoniazid and 

rifampin, the two best first-line TB 

treatment drugs

Extensively 

drug-resistant 

(XDR TB)

Resistant to isoniazid and rifampin, 

PLUS resistant to any fluoroquinolone 

AND at least 1 of the 3 injectable 

second-line drugs (e.g., amikacin, 

kanamycin, or capreomycin)

5. Bacteriologic Examination (24)

Growth-Based Drug Susceptibility Testing

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 124

• Growth-based susceptibility testing can be done 

using a liquid or solid medium method

• Organisms that grow in media containing a specific 

drug are considered resistant to that drug

• Liquid medium methods are faster than solid media 

methods for determining susceptibility to first-line 

TB medications

• Results can be obtained within 7 to 14 days for 

liquid medium method and up to 21 days for solid 

medium method

5. Bacteriologic Examination (25)

Molecular Detection of Drug Resistance

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 125

• Molecular tests provide preliminary guidance on 

effective therapy for TB patients

• These tests should be considered for patients 

with the following characteristics:

– High risk of rifampin resistance, including MDR TB;

– First-line drug susceptibility results are available and 

show resistance to rifampin;

– Infectiousness poses a risk to vulnerable contacts; and

– Contraindications to essential first-line medications

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 126

Why is it necessary to culture a specimen?

Culture Specimen

Study Question 3.32
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

22

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 127

Culture Specimen

Study Question 3.33

What does a positive culture for 

M. tuberculosis mean? How is this important 

for the TB diagnosis?

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 128

Why are drug susceptibility tests done?

Drug Susceptibility

Study Question 3.34

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 129

Drug Susceptibility

Study Question 3.35

How often should drug susceptibility tests be 

done?

130

Reporting TB Cases

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 131

Reporting TB Cases 

• TB programs report 

TB cases to CDC 

using a standard case 

report form called the 

Report of Verified of 

Case of Tuberculosis

(RVCT)

– All cases that meet 

criteria are called 

verified TB cases

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 132

Criteria for Reporting TB Cases (1)

Cases that meet one of these four sets of 

criteria are counted as verified TB cases:

1. Patient has positive culture for M. 

tuberculosis

2. Patient has positive NAA test for M. 

tuberculosis

• NAA test must be accompanied by 

culture for mycobacteria species
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

23

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 133

Criteria for Reporting TB Cases (2)

3. Patient has positive AFB smear, but culture 

has not been obtained or is falsely negative 

or contaminated

4. In the absence of laboratory confirmation, 

patient meets all of the following criteria:

• Positive TST or IGRA,

• Other signs and symptoms of TB disease,

• Treatment with 2 or more TB drugs, and

• A completed diagnostic evaluation.

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 134

Criteria for Reporting TB Cases (3)

• Cases that do not meet any of these sets of 

criteria may be counted as a verified TB case 

if health care provider has reported the case 

and decided to treat the patient for TB 

disease

135

Case Studies

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 136

Module 3: Case Study 3.1

Which of the following patients have a positive TST

reaction? Circle the best answer(s).

a. Mr. West, 36 yrs. old, HIV infected, 8 mm induration

b. Ms. Hernandez, 26 yrs. old, native of Mexico, 7 mm induration

c. Ms. Jones, 56 yrs. old, diabetic, 12 mm induration

d. Mr. Sung, 79 yrs. old, nursing home resident, 11 mm induration

e. Mr. Williams, 21 yrs. old, no known risk factors, 13 mm 

induration

f. Ms. Marcos, 42 yrs. old, chest x-rays findings suggestive of 

previous TB, 6 mm induration

g. Ms. Rayle, 50 yrs. old, husband has pulmonary TB, 9 mm of 

induration

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 137

Module 3: Case Study 3.2 (1)

A 30 year-old man who recently immigrated 

to the United States from India is given a TST 

and found to have 14 mm of induration. He 

reports that he was vaccinated with BCG as a 

child. He also says that his wife was treated 

for pulmonary TB disease last year. 

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 138

How should this man’s results be interpreted?

What factors make it more likely that this man’s 

positive reaction is due to TB infection?

Module 3: Case Study 3.2 (2)
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

24

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 139

Module 3: Case Study 3.3 (1)

Mr. Bell comes to the TB clinic for a TST. He 

believes that he has been exposed to TB, and 

he knows he is at high risk for TB because 

he is HIV infected. He is given a TST, and his 

reaction is read 48 hours later as 0 mm of 

induration. 

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 140

What are 3 ways to interpret this result?

Module 3: Case Study 3.3 (2)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 141

Module 3: Case Study 3.4 (1)

Ms. Wilson is a 60-year-old nurse. When she 

started a job at the local hospital, she was 

given a TST, her first test in 25 years. Her 

reaction was read 48 hours later as 0 mm 

induration. Six months later, she was 

retested as part of the TB testing program in 

the unit where she works. Her skin test 

reaction was read 48 hours later as 11 mm of 

induration.

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 142

What are 2 ways to interpret this result?

Module 3: Case Study 3.4 (2)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 143

Module 3: Case Study 3.5 (1)

Mr. Lee has a cough and other symptoms of 

TB disease, and he is evaluated with a chest 

x-ray. However, he is unable to cough up 

any sputum on his own for the bacteriologic 

examination.

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 144

What should be done?

Module 3: Case Study 3.5 (2)
Module 3 – Targeted Testing and the Diagnosis of Latent Tuberculosis Infection 

and Tuberculosis Disease

25

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 145

Module 3: Case Study 3.6 (1)

Ms. Thompson gave three sputum 

specimens, which were sent to the laboratory 

for smear examination and culture. The 

smear results were reported as 4+, 3+, and 

4+.

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 146

What do these results tell you about Ms. 

Thompson’s diagnosis and her 

infectiousness?

Module 3: Case Study 3.6 (2)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 147

Module 3: Case Study 3.7 (1)

Mr. Sagoo has symptoms of TB disease and 

a cavity on his chest x-ray, but all of his 

sputum smears are negative for acid-fast 

bacilli.

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 148

Does this rule out the diagnosis of 

pulmonary TB disease?

Why or why not?

Module 3: Case Study 3.7 (2)

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 149

Module 3: Case Study 3.8 (1)

In the public health clinic, you see a patient, 

Ms. Sanchez, who complains of weight loss, 

fever, and a cough of 4 weeks duration. 

When questioned, she reports that she has 

been treated for TB disease in the past and 

that she occasionally injects heroin.

Module 3 – Targeted Testing and the Diagnosis of 

Latent Tuberculosis Infection and Tuberculosis Disease 150

What parts of Ms. Sanchez’s medical history 

lead you to suspect TB disease?

What diagnostic tests should be done?

Module 3: Case Study 3.8 (2)