Hemoglobin A1c testing can be used to screen for and diagnose diabetes (type 1 or type 2), to assess the risk of developing diabetes and to monitor glycemic control/treatment in patients with diabetes. Testing should be performed routinely in all patients with diabetes at initial assessment and either twice per year in patients who are meeting treatment goals or quarterly in patients whose therapy has recently changed and/or are not meeting glycemic goals.
Guidelines for Test Utilization
What does the test tell me?
Hemoglobin A1c reflects the mean blood glucose over the last 2 to 3 months by measuring the percentage of glycated hemoglobin in the blood. A1c ≥ 6.5% is one of the diagnostic criteria for diabetes (with diagnosis requiring two abnormal test results in the absence of unequivocal hyperglycemia), while an A1c of 5.7-6.4% indicates prediabetes. A therapeutic target of <7.0% can be used for non-pregnant children, adolescents, or adults with diabetes, or <8.0% for those with limited life expectancy or where the harms of treatment outweigh the benefits. [back to top]
When should I order this test?
This test can be ordered to screen for diabetes or to diagnose patients with symptoms suggestive of diabetes. It can also be ordered in asymptomatic children or adults who are overweight or obese and have one or more risk factors for diabetes. Hemoglobin A1c should be ordered on all patients, starting at 45 years of age and thereafter at 3-year intervals if results are normal. In patients with prediabetes, hemoglobin A1c testing should be ordered yearly. To monitor patients with diabetes, hemoglobin A1c should be ordered at least twice yearly in patients who have achieved stable glycemic control and quarterly in patients whose treatment has recently changed or who are not meeting their goals. [back to top]
When should I NOT order this test?
Hemoglobin A1c should not be ordered more frequently than every 3 months. Do not order this test to screen for or diagnose gestational diabetes or cystic fibrosis-related diabetes. Do not order this test in patients with altered red blood cell turnover. Examples of such conditions include anemia, hemoglobinopathies, recent blood loss or transfusion, pregnancy, erythropoietin therapy and hemolysis. [back to top]
How should I interpret the result?
Hemoglobin A1c < 5.7% = No diabetes
Hemoglobin A1c 5.7-6.4% = Prediabetes
Hemoglobin A1c ≥ 6.5% = Diabetes
<7.0% as therapeutic target for non-pregnant children or adults with diabetes, or <8.0% for those with limited life expectancy or where the harms of treatment outweigh the benefits. [back to top]
Is the test result diagnostic/confirmatory of the condition? If not, is there a diagnostic/confirmatory test?
Yes. A Hemoglobin A1c result of 5.7-6.4% indicates prediabetes while a result of ≥ 6.5% is one of four diagnostic criteria for diabetes. In the absence of unequivocal hyperglycemia, diagnosis of diabetes requires 2 abnormal tests – either 2 different abnormal tests from the same sample, or abnormal results from two separate samples. [back to top]
Are there factors that can affect the lab result?
Conditions associated with altered red blood cell turnover will affect the hemoglobin A1c result. Hemoglobin A1c testing for the purpose of screening and/or diagnosing diabetes should only be performed using an NGSP-certified method that is standardized to the DCCT reference assay. The use of point-of-care hemoglobin A1c tests to diagnose diabetes is not recommended as they may give inaccurate results due to interference from certain hemoglobin variants; they can however be used for monitoring purposes. HbA1c methods differ in their susceptibility to interference from hemoglobin variants, so providers caring for affected patients should consult their clinical laboratory to determine if their A1c assay will provide accurate results. [back to top]
Are there considerations for special populations?
Epidemiological studies on the use of hemoglobin A1c to diagnose diabetes have been performed primarily in adult populations. Based on the risk of diabetes (high-risk vs. low-risk), the ADA provides guideline recommendations on when to start, and the frequency of, testing. Also, it is recommended to test one year post transplant to pick up any transplant induced diabetes. [back to top]
What other test(s) might be indicated?
Fasting plasma glucose, random plasma glucose, and oral glucose tolerance tests can also be used to screen for and diagnose prediabetes and diabetes. Unlike hemoglobin A1c, these tests provide a snapshot of the individual’s current blood glucose level. Autoantibody testing and C-peptide may aid in the differentiation between type 1 diabetes versus other forms of diabetes.
If hemoglobin A1c cannot be used, fructosamine, glycated albumin, or 1,5, anhydroglucitol can be considered.
Fructosamine and glycated albumin reflect mean blood glucose over the last 2-3 weeks, whereas 1,5 anhydroglucitol reflects mean blood glucose over a 24-hour period. [back to top]
References
American Diabetes Association. Classification and Diagnosis of Diabetes. Diabetes Care. 2021;44(Suppl. 1): S15–S33
Driskell, Owen J. et.al. Reduced Testing Frequency for Glycated Hemoglobin, HbA1c, Is Associated With Deteriorating Diabetes Control. Diabetes Care. Oct 2014; 37(10): 2731-2737
Lisi, Donna. Applying recent A1c recommendations in clinical practice. U.S. Pharmacist. 2018; 43. 15-22
Last reviewed: February 2024. The content for Optimal Testing: the Association for Diagnostics & Laboratory Medicine’s (ADLM) Guide to Lab Test Utilization has been developed and approved by the the Academy of Diagnostics & Laboratory Medicine and ADLM’s Science and Practice Core Committee.
As the fields of laboratory medicine and diagnostic testing continue to grow at an incredible rate, the knowledge and expertise of clinical laboratory professionals is essential to ensure that patients received the highest quality and most useful laboratory tests. ADLM’s Academy and Science and Practice Core Committee have developed a test utilization resource focusing on commonly misused tests in hospitals and clinics. Improper test utilization can result in poor patient outcomes and waste in the healthcare system. This important resource geared toward medical professionals recommends better tests and diagnostic practices. Always consult your laboratory director to make sure these recommendations are appropriate for your patient population.