The A1C Test 

and Diabetes

National Diabetes Information Clearinghouse

U.S. Department 

of Health and 

Human Services

NATIONAL 

INSTITUTES 

OF HEALTH

What is the A1C test?

The A1C test is a blood test that provides 

information about a person’s average levels 

of blood glucose, also called blood sugar, 

over the past 3 months. The A1C test is 

sometimes called the hemoglobin A1c, 

HbA1c, or glycohemoglobin test. The A1C 

test is the primary test used for diabetes management and diabetes research. 

How does the A1C test work?

The A1C test is based on the attachment 

of glucose to hemoglobin, the protein in 

red blood cells that carries oxygen. In the 

body, red blood cells are constantly forming 

and dying, but typically they live for about 

3 months. Thus, the A1C test reflects the 

average of a person’s blood glucose levels 

over the past 3 months. The A1C test result 

is reported as a percentage. The higher the 

percentage, the higher a person’s blood glucose levels have been. A normal A1C level is 

below 5.7 percent. 

Can the A1C test be used to 

diagnose type 2 diabetes and 

prediabetes?

Yes. In 2009, an international expert committee recommended the A1C test as one 

of the tests available to help diagnose type 2 

diabetes and prediabetes.1 Previously, only 

the traditional blood glucose tests were used 

to diagnose diabetes and prediabetes. 

1The International Expert Committee. International 

Expert Committee report on the role of the A1C 

assay in the diagnosis of diabetes. Diabetes Care. 

2009;32(7):1327–1334.

Because the A1C test does not require fasting and blood can be drawn for the test at 

any time of day, experts are hoping its convenience will allow more people to get tested—

thus, decreasing the number of people with 

undiagnosed diabetes. However, some medical organizations continue to recommend 

using blood glucose tests for diagnosis.

Why should a person be 

tested for diabetes?

Testing is especially important because 

early in the disease diabetes has no symptoms. Although no test is perfect, the 

A1C and blood glucose tests are the best 

tools available to diagnose diabetes—a 

serious and lifelong disease. 

Testing enables health care providers 

to find and treat diabetes before complications occur and to find and treat 

prediabetes, which can delay or prevent 

type 2 diabetes from developing.
2    The A1C Test and Diabetes

Has the A1C test improved?

Yes.  A1C laboratory tests are now standardized.  In the past, the A1C test was not recommended for diagnosis of type 2 diabetes 

and prediabetes because the many different 

types of A1C tests could give varied results.  

The accuracy has been improved by the 

National Glycohemoglobin Standardization 

Program (NGSP), which developed standards for the A1C tests.  

The NGSP certifies that manufacturers of 

A1C tests provide tests that are consistent 

with those used in a major diabetes study.  

The study established current A1C goals for 

blood glucose control that can reduce the 

occurrence of diabetes complications, such as 

blindness and blood vessel disease.2

2Nathan DM, Genuth S, Lachin J, et al.  The effect of 

intensive treatment of diabetes on the development 

and progression of long-term complications in insulindependent diabetes mellitus.  The New England Journal 

of Medicine.  1993:329(14)977–986.

How is the A1C test used to 

diagnose type 2 diabetes and 

prediabetes?

The A1C test can be used to diagnose type 2 

diabetes and prediabetes alone or in combination with other diabetes tests.  When 

the A1C test is used for diagnosis, the blood 

sample must be sent to a laboratory that uses 

an NGSP-certified method for analysis to 

ensure the results are standardized.  

Blood samples analyzed in a health care provider’s office, known as point-of-care (POC) 

tests, are not standardized for diagnosing 

diabetes.  The following table provides the 

percentages that indicate diagnoses of normal, diabetes, and prediabetes according to 

A1C levels.

Diagnosis* A1C Level

Normal below 5.7 percent

Diabetes 6.5 percent or above

Prediabetes 5.7 to 6.4 percent

*Any test for diagnosis of diabetes requires 

confirmation with a second measurement unless 

there are clear symptoms of diabetes.

Having prediabetes is a risk factor for getting 

type 2 diabetes.  People with prediabetes 

may be retested each year.  Within the 

prediabetes A1C range of 5.7 to 6.4 percent, 

the higher the A1C, the greater the risk of 

diabetes.  Those with prediabetes are likely 

to develop type 2 diabetes within 10 years, 

but they can take steps to prevent or delay 

diabetes. 
3    The A1C Test and Diabetes

Is the A1C test used during 

pregnancy? 

The A1C test may be used at the first visit to 

the health care provider during pregnancy 

to see if women with risk factors had undiagnosed diabetes before becoming pregnant.  

After that, the oral glucose tolerance test 

(OGTT) is used to test for diabetes that 

develops during pregnancy—known as gestational diabetes.  After delivery, women who 

had gestational diabetes should be tested 

for persistent diabetes.  Blood glucose tests, 

rather than the A1C test, should be used for 

testing within 12 weeks of delivery.

More information about diagnosing and 

treating gestational diabetes is available 

in the National Diabetes Information 

Clearinghouse’s (NDIC’s) publication 

What I need to know about Gestational 

Diabetes, available at www.diabetes.niddk.

nih.gov or by calling 1–800–860–8747.

Can blood glucose tests still 

be used for diagnosing type 2 

diabetes and prediabetes?

Yes.  The standard blood glucose tests 

used for diagnosing type 2 diabetes and 

prediabetes—the fasting plasma glucose 

(FPG) test and the OGTT—are still 

recommended.  The random plasma glucose 

test, also called the casual glucose test, 

may be used for diagnosing diabetes when 

symptoms of diabetes are present.  In some 

cases, the A1C test is used to help health 

care providers confirm the results of a blood 

glucose test.  

Can the A1C test result in a 

different diagnosis than the 

blood glucose tests? 

Yes.  In some people, a blood glucose test 

may indicate a diagnosis of diabetes while 

an A1C test does not.  The reverse can also 

occur—an A1C test may indicate a diagnosis 

of diabetes even though a blood glucose test 

does not.  Because of these variations in test 

results, health care providers repeat tests 

before making a diagnosis.  

People with differing test results may be in 

an early stage of the disease, where blood 

glucose levels have not risen high enough 

to show on every test.  Sometimes, making 

simple changes in lifestyle—losing a small 

amount of weight and increasing physical 

activity—can help people in this early stage 

reverse diabetes or delay its onset.  

More information about diagnosing 

diabetes and prediabetes is available 

in the NDIC’s fact sheet Diagnosis of 

Diabetes, available at www.diabetes.niddk.

nih.gov or by calling 1–800–860–8747.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Are diabetes blood test results always accurate? 

All laboratory test results can vary from day to day and from test to test. Results can vary 

• within the person being tested. A person’s blood glucose levels normally move up and 

down depending on meals, exercise, sickness, and stress. 

• between different tests. Each test measures blood glucose levels in a different way. 

For example, the FPG test measures glucose that is floating free in the blood after fasting and only shows the blood glucose level at the time of the test. Repeated blood glucose tests, such as self-monitoring several times a day with a home meter, can record 

the natural variations of blood glucose levels during the day. The A1C test represents 

the amount of glucose attached to hemoglobin, so it reflects an average of all the blood 

glucose levels a person may experience over 3 months. The A1C test will not show 

day-to-day changes. 

The following chart shows how multiple blood glucose measurements over 4 days compare with an A1C measurement. 

Blood Glucose Measurements Compared with A1C Measurements Over 4 Days 

Note: Blood glucose 

(mg/dL) measurements 

were taken four times 

per day (fasting or 

pre-breakfast, prelunch, pre-dinner, and 

bedtime). 

The straight black 

line indicates an A1C 

measurement of 

7.0 percent. The blue 

line shows blood glucose 

test results from selfmonitoring four times a 

day over a 4-day period. 

• within the same test. Even when the same blood sample is repeatedly measured in the 

same laboratory, the results may vary due to small changes in temperature, equipment, 

or sample handling. 

Health care providers take these variations into account when considering test results and 

repeat laboratory tests for confirmation. Diabetes develops over time, so even with variations in test results, health care providers can tell when overall blood glucose levels are 

becoming too high. 

Comparing test results from different laboratories can be misleading. People should consider requesting new laboratory tests when they change health care providers, or if their 

health care provider’s office changes the laboratory or clinic it uses for blood testing. 

4 The A1C Test and Diabetes 
 

 

 

 

 

 

 

How accurate is the A1C test? 

The A1C test result can be up to 0.5 percent 

higher or lower than the actual percentage. 

This means an A1C measured as 7.0 percent 

could indicate a true A1C anywhere in the 

range from 6.5 to 7.5 percent. Health care 

providers can visit www.ngsp.org to find information about the accuracy of the A1C test 

used by their laboratory. 

The drawing below shows the range of variation that can occur when an A1C is 7.0 percent on the lab report. 

Courtesy of David Aron, M.D., Louis Stokes Department of Veterans Affairs Medical Center 

To put the A1C test into perspective, an FPG 

test result of 126 mg/dL could indicate a 

true FPG anywhere in the range from 110 to 

142 mg/dL. This variation will be even 

greater if the blood sample is not processed 

promptly or is not put on ice, causing blood 

glucose levels in the sample to decrease. The 

drawing below shows the range of variation 

that can occur when the FPG is 126 mg/dL. 

Courtesy of David Aron, M.D., Louis Stokes Department of Veterans Affairs Medical Center 

5 The A1C Test and Diabetes 

Can the A1C test give false 

results? 

Yes, for some people. The A1C test can 

be unreliable for diagnosing or monitoring 

diabetes in people with certain conditions 

that are known to interfere with the results. 

Interference should be suspected when A1C 

results seem very different from the results 

of a blood glucose test. 

People of African, Mediterranean, or Southeast Asian descent, or people with family 

members with sickle cell anemia or a thalassemia are particularly at risk of interference. 

People in these groups may have a less common type of hemoglobin, known as a hemoglobin variant, that can interfere with some 

A1C tests. Most people with a hemoglobin 

variant have no symptoms and may not know 

that they carry this type of hemoglobin. 

Not all of the A1C tests are unreliable for 

people with a hemoglobin variant. People 

with false results from one type of A1C test 

may need a different type of A1C test for 

measuring their average blood glucose level. 

The NGSP provides information for health 

care providers about which A1C tests are 

appropriate to use for specific hemoglobin 

variants at www.ngsp.org. 
6    The A1C Test and Diabetes

More information about problems with 

the A1C test and different forms of sickle 

cell anemia is available in the following 

NDIC publications: 

• For People of African, Mediterranean, 

or Southeast Asian Heritage: Important Information about Diabetes 

Blood Tests  

• Sickle Cell Trait and Other Hemoglobinopathies and Diabetes: Important 

Information for Physicians

These publications are available at 

www.diabetes.niddk.nih.gov or by calling 

1–800–860–8747.

False A1C results may also occur in people 

with other problems that affect their blood or 

hemoglobin.  For example, a falsely low A1C 

result can occur in people with

•  anemia

• heavy bleeding

A falsely elevated A1C result can occur in 

people who

•  are very low in iron, for example, those 

with iron deficiency anemia

Other causes of abnormal A1C results 

include 

•  kidney failure 

•  liver disease

How is the A1C test used 

after diagnosis of diabetes?

Health care providers can use the A1C test 

to monitor blood glucose levels in people 

with type 1 or type 2 diabetes.  The A1C test 

is not used to monitor gestational diabetes.  

The American Diabetes Association recommends that people with diabetes who are 

meeting treatment goals and have stable 

blood glucose levels have the A1C test twice 

a year.  Health care providers may repeat the 

A1C test as often as four times a year until 

blood glucose levels reach recommended 

levels.  

The A1C test helps health care providers adjust medication to reduce the risk of 

long-term diabetes complications.  Studies 

have demonstrated substantial reductions in 

long-term complications with the lowering of 

A1C levels.  

When the A1C test is used for monitoring 

blood glucose levels in a person with diabetes, the blood sample can be analyzed in a 

health care provider’s office using a POC test 

to give immediate results.  However, POC 

tests are less reliable and not as accurate as 

most laboratory tests.  
 

How does the A1C relate to 

estimated average glucose? 

Estimated average glucose (eAG) is calculated from the A1C. Some laboratories 

report eAG with the A1C test results. The 

eAG number helps people with diabetes 

relate their A1C to daily glucose monitoring 

levels. The eAG calculation converts the 

A1C percentage to the same units used by 

home glucose meters—milligrams per deciliter (mg/dL). 

The eAG number will not match daily 

glucose readings because it is a long-term 

average rather than the blood glucose level 

at a single time, as measured with the home 

glucose meter. The following table shows the 

relationship between the A1C and the eAG. 

Relationship between A1C and eAG 

A1C eAG 

Percent mg/dL 

6 126 

7 154 

8 183 

9 212 

10 240 

11 269 

12 298 

Source: Adapted from American Diabetes Association. 

Standards of medical care in diabetes—2011. Diabetes 

Care. 2011;34(Supp 1):S11–S61, table 9. 

7 The A1C Test and Diabetes 
 

What A1C target should 

people have? 

People will have different A1C targets 

depending on their diabetes history and their 

general health. People should discuss their 

A1C target with their health care provider. 

Studies have shown that people with diabetes 

can reduce the risk of diabetes complications 

by keeping A1C levels below 7 percent. 

Maintaining good blood glucose control will 

benefit those with new-onset diabetes for 

many years to come. However, an A1C level 

that is safe for one person may not be safe 

for another. For example, keeping an A1C 

level below 7 percent may not be safe if it 

leads to problems with hypoglycemia, also 

called low blood glucose. 

Less strict blood glucose control, or an A1C 

between 7 and 8 percent—or even higher in 

some circumstances—may be appropriate in 

people who have 

• limited life-expectancy 

• long-standing diabetes and difficulty 

attaining a lower goal

• severe hypoglycemia 

• advanced diabetes complications such as 

chronic kidney disease, nerve problems, 

or cardiovascular disease 

Will the A1C test show 

changes in blood glucose 

levels? 

Large changes in a person’s blood glucose 

levels over the past month will show up in 

their A1C test result, but the A1C does 

not show sudden, temporary increases or 

decreases in blood glucose levels. Even 

though the A1C represents a long-term 

average, blood glucose levels within the past 

30 days have a greater effect on the A1C 

reading than those in previous months. 

8 The A1C Test and Diabetes 
9    The A1C Test and Diabetes

Points to Remember 

• The A1C test is a blood test that 

provides information about a person’s average levels of blood glucose, 

also called blood sugar, over the past 

3 months.  

• The A1C test is based on the attachment of glucose to hemoglobin, the 

protein in red blood cells that carries 

oxygen.  Thus, the A1C test reflects 

the average of a person’s blood glucose 

levels over the past 3 months.  

• In 2009, an international expert committee recommended the A1C test 

be used as one of the tests available 

to help diagnose type 2 diabetes and 

prediabetes.    

• Because the A1C test does not require 

fasting and blood can be drawn for 

the test at any time of day, experts are 

hoping its convenience will allow more 

people to get tested—thus, decreasing 

the number of people with undiagnosed diabetes.

• In the past, the A1C test was not 

recommended for diagnosis of type 2 

diabetes and prediabetes because the 

many different types of A1C tests 

could give varied results.  The accuracy 

has been improved by the National 

Glycohemoglobin Standardization 

Program (NGSP), which developed 

standards for the A1C tests.  Blood 

samples analyzed in a health care provider’s office, known as point-of-care 

(POC) tests, are not standardized for 

use in diagnosing diabetes.  

• The A1C test may be used at the first 

visit to the health care provider during pregnancy to see if women with 

risk factors had undiagnosed diabetes 

before becoming pregnant.  After that, 

the oral glucose tolerance test (OGTT) 

is used to test for diabetes that develops during pregnancy—known as 

gestational diabetes.  

• The standard blood glucose tests 

used for diagnosing type 2 diabetes 

and prediabetes—the fasting plasma 

glucose (FPG) test and the OGTT—

are still recommended.  The random 

plasma glucose test may be used for 

diagnosing diabetes when symptoms 

of diabetes are present.  

• The A1C test can be unreliable for 

diagnosing or monitoring diabetes in 

people with certain conditions that are 

known to interfere with the results.  

• The American Diabetes Association 

recommends that people with diabetes 

who are meeting treatment goals and 

have stable blood glucose levels have 

the A1C test twice a year.  

• Estimated average glucose (eAG) 

is calculated from the A1C to help 

people with diabetes relate their A1C 

to daily glucose monitoring levels.  

• People will have different A1C targets 

depending on their diabetes history 

and their general health.  People 

should discuss their A1C target with 

their health care provider.   
 

 

Hope through Research 

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) conducts 

and supports research related to the causes, 

treatment, and prevention of diabetes. Many 

ongoing research studies use the A1C test to 

measure and compare the success of different 

treatments or medications for diabetes care. 

In addition, researchers continue to improve 

measurement of A1C. 

Participants in clinical trials can play a more 

active role in their own health care, gain 

access to new research treatments before 

they are widely available, and help others 

by contributing to medical research. For 

information about current studies, visit 

www.ClinicalTrials.gov. 

For More Information 

American Diabetes Association 

1701 North Beauregard Street 

Alexandria, VA 22311 

Phone: 1–800–DIABETES (1–800–342–2383) 

Fax: 703–549–6995 

Email: AskADA@diabetes.org 

Internet: www.diabetes.org 

Juvenile Diabetes Research Foundation 

International 

26 Broadway, 14th Floor 

New York, NY 10004 

Phone: 1–800–533–CURE (1–800–533–2873) 

Fax: 212–785–9595 

Email: info@jdrf.org 

Internet: www.jdrf.org 

10 The A1C Test and Diabetes 
11    The A1C Test and Diabetes

Acknowledgments

Publications produced by the Clearinghouse 

are carefully reviewed by both NIDDK 

scientists and outside experts.  This publication was reviewed by Randie Little, Ph.D., 

University of Missouri-Columbia; David 

B. Sacks, M.B., Ch.B., F.R.C.Path., NIH 

Clinical Center; and Leonard Pogach M.D., 

M.B.A., F.A.C.P., Medical Service, Veterans 

Affairs Central Office. 

You may also find additional information about this 

topic by visiting MedlinePlus at www.medlineplus.gov.

This publication may contain information about 

medications.  When prepared, this publication 

included the most current information available.   

For updates or for questions about any medications, 

contact the U.S. Food and Drug Administration tollfree at 1–888–INFO–FDA (1–888–463–6332) or visit 

www.fda.gov.  Consult your health care provider for 

more information.

The U.S. Government does not endorse or favor any 

specific commercial product or company.  Trade, 

proprietary, or company names appearing in this 

document are used only because they are considered 

necessary in the context of the information provided.  

If a product is not mentioned, the omission does not 

mean or imply that the product is unsatisfactory.
 

 

 

 

 

 

National Diabetes Education 

Program 

1 Diabetes Way 

Bethesda, MD 20814–9692 

Phone: 1–888–693–NDEP 

(1–888–693–6337) 

TTY: 1–866–569–1162 

Fax: 703–738–4929 

Email: ndep@mail.nih.gov 

Internet: www.ndep.nih.gov 

www.yourdiabetesinfo.org 

The National Diabetes Education Program 

is a federally funded program sponsored by 

the U.S. Department of Health and Human 

Services’ National Institutes of Health 

and the Centers for Disease Control and 

Prevention and includes over 200 partners at 

the federal, state, and local levels, working 

together to reduce the morbidity and 

mortality associated with diabetes. 

National Diabetes 

Information Clearinghouse 

1 Information Way 

Bethesda, MD 20892–3560 

Phone: 1–800–860–8747 

TTY: 1–866–569–1162 

Fax: 703–738–4929 

Email: ndic@info.niddk.nih.gov 

Internet: www.diabetes.niddk.nih.gov 

The National Diabetes Information 

Clearinghouse (NDIC) is a service of the 

National Institute of Diabetes and Digestive 

and Kidney Diseases (NIDDK). The 

NIDDK is part of the National Institutes of 

Health of the U.S. Department of Health 

and Human Services. Established in 1978, 

the Clearinghouse provides information 

about diabetes to people with diabetes and 

to their families, health care professionals, 

and the public. The NDIC answers inquiries, 

develops and distributes publications, and 

works closely with professional and patient 

organizations and Government agencies to 

coordinate resources about diabetes. 

This publication is not copyrighted. The Clearinghouse 

encourages users of this publication to duplicate and 

distribute as many copies as desired. 

This publication is available at 

www.diabetes.niddk.nih.gov. 

U.S. DEPARTMENT OF HEALTH 

AND HUMAN SERVICES 

National Institutes of Health 

NIH Publication No. 11–7816 

September 2011 

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