TB Elimination

Diagnosis of Tuberculosis Disease

National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention

Division of Tuberculosis Elimination

CS227840_C

When Should You Suspect 

Tuberculosis (TB)?

TB is a disease caused by Mycobacterium 

tuberculosis. TB disease should be suspected in 

persons who have the following symptoms:

• Unexplained weight loss 

• Loss of appetite 

• Night sweats 

• Fever 

• Fatigue 

If TB disease is in the lungs (pulmonary), 

symptoms may include: 

• Coughing for ≥3 weeks 

• Hemoptysis (coughing up blood) 

• Chest pain 

If TB disease is in other parts of the body 

(extrapulmonary), symptoms will depend on 

the area affected.

How Do You Evaluate Persons 

Suspected of Having TB Disease?

A complete medical evaluation for TB includes 

the following:

1. Medical History

Clinicians should ask about the patient’s 

history of TB exposure, infection, or disease. 

It is also important to consider demographic 

factors (e.g., country of origin, age, ethnic or 

racial group, occupation) that may increase the 

patient’s risk for exposure to TB or to drugresistant TB. Also, clinicians should determine 

whether the patient has medical conditions, 

especially HIV infection, that increase the risk 

of latent TB infection progressing to TB disease. 

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2. Physical Examination

A physical exam can provide valuable 

information about the patient’s overall 

condition and other factors that may affect 

how TB is treated, such as HIV infection or 

other illnesses. 

3. Test for TB Infection

The Mantoux tuberculin skin test (TST) or 

the TB blood test can be used to test for 

M. tuberculosis infection. Additional tests are 

required to confirm TB disease. The Mantoux 

tuberculin skin test is performed by injecting 

a small amount of fluid called tuberculin into 

the skin in the lower part of the arm. The test 

is read within 48 to 72 hours by a trained 

health care worker, who looks for a reaction 

(induration) on the arm.

The TB blood test measures the patient’s 

immune system reaction to M. tuberculosis.

4. Chest Radiograph

A posterior-anterior chest radiograph is used 

to detect chest abnormalities. Lesions may 

appear anywhere in the lungs and may differ 

in size, shape, density, and cavitation. These 

abnormalities may suggest TB, but cannot be 

used to definitively diagnose TB. However, a 

chest radiograph may be used to rule out the 

possibility of pulmonary TB in a person who 

has had a positive reaction to a TST or TB blood 

test and no symptoms of disease. 
5. Diagnostic Microbiology

The presence of acid-fast-bacilli (AFB) 

on a sputum smear or other specimen 

often indicates TB disease. Acid-fast 

microscopy is easy and quick, but it 

does not confirm a diagnosis of TB 

because some acid-fast-bacilli are not 

M. tuberculosis. Therefore, a culture is 

done on all initial samples to confirm the 

diagnosis. (However, a positive culture 

is not always necessary to begin or 

continue treatment for TB.) A positive 

culture for M. tuberculosis confirms 

the diagnosis of TB disease. Culture 

examinations should be completed on 

all specimens, regardless of AFB smear 

results. Laboratories should report 

positive results on smears and cultures 

within 24 hours by telephone or fax to 

the primary health care provider and to 

the state or local TB control program, as 

required by law. 

6. Drug Resistance

For all patients, the initial M. tuberculosis

isolate should be tested for drug 

resistance. It is crucial to identify drug 

resistance as early as possible to ensure 

effective treatment. Drug susceptibility 

patterns should be repeated for patients 

who do not respond adequately to 

treatment or who have positive culture 

results despite 3 months of therapy. 

Susceptibility results from laboratories 

should be promptly reported to the 

primary health care provider and the 

state or local TB control program. 

Additional Information

1. American Thoracic Society (ATS) and CDC. 

Diagnostic standards and classification of 

tuberculosis in adults and children. (PDF) 

Am J Respir Crit Care Med 2000; 161. 

http://ajrccm.atsjournals.org/cgi/content/

full/161/4/1376

2. ATS, CDC, and Infectious Diseases Society of 

America. Treatment of tuberculosis. MMWR

2003; 52 (No. RR-11). http://www.cdc.gov/

mmwr/PDF/rr/rr5211.pdf

3. Centers for Disease Control and Prevention. 

Guidelines for the investigation of contacts 

of persons with infectious tuberculosis and 

Guidelines for using the QuantiFERON®-

TB Gold test for detecting Mycobacterium 

tuberculosis infection, United States. 

MMWR 2005; 54 (No. RR-15). http://www.

cdc.gov/mmwr/pdf/rr/rr5415.pdf

4. Updated Guidelines for the Use of Nucleic 

Acid Amplification Tests in the Diagnosis of 

Tuberculosis. MMWR 2009;58(1). 

http://www.cdc.gov/mmwr/

preview/mmwrhtml/mm5801a3.

htm?scid=mm5801a3_e

http://www.cdc.gov/tb

October 2011