Hemoglobin A1c (A1c): Optimal Testing Recommendations
A1c testing can be used to screen for and diagnose diabetes in adults, to assess the risk of developing diabetes and to monitor treatment in diabetic patients. Testing should be performed routinely in all diabetic patients 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?
A1c evaluates the glycemic control over the last 2 to 3 months by measuring the percentage of glycated hemoglobin in the blood. A1c ≥ 6.5% is diagnostic of diabetes while an A1c of 5.7-6.4 % indicates prediabetes. A therapeutic target of <7.0% can be used for non-pregnant adult diabetics, 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 adults for diabetes or to diagnose patients with symptoms suggestive of diabetes. It can also be ordered in asymptomatic adults who are overweight or obese and have one or more risk factors for diabetes. A1c should be ordered on all patients, starting at 45 years of age and thereafter at 3-year intervals if results are normal 1. In prediabetic patients, A1c testing should be ordered yearly. To monitor diabetic patients, 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?
A1c should not be ordered more frequently than every 3 months 2. 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 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?
A1c < 5.7% = No diabetes
A1c 5.7-6.4% = Prediabetes
A1c ≥ 6.5% = Diabetes
<7.0% as therapeutic target for non-pregnant adult diabetics, 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. An A1c result of 5.7-6.4 % indicates prediabetes while a result of ≥ 6.5% is diagnostic for diabetes. In the absence of unequivocal hyperglycemia, A1c results should be repeated using a new blood sample to confirm the diagnosis of diabetes. [back to top]
Are there factors that can affect the lab result?
Conditions associated with altered red blood cell turnover will affect the A1c result. 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 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. [back to top]
Are there considerations for special populations?
Epidemiological studies on the use of A1c to diagnose diabetes have been performed primarily in adult populations. For this reason, it is unclear if A1c, and what cutoff, should be used to diagnose diabetes in children and adolescents. 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. [back to top]
What other test(s) might be indicated?
Fasting plasma glucose and oral glucose tolerance tests can also be used to screen for and diagnose prediabetes and diabetes. Unlike A1c, these tests provide a snapshot of the individual’s current blood glucose level. Autoantibody testing may aid in the differentiation between type 1 diabetes versus other forms of diabetes.
If A1c cannot be used, fructosamine, glycated albumin, or 1,5, anhydroglucitol should be considered. [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: March 2022. The content for Optimal Testing: AACC's Guide to Lab Test Utilization has been developed and approved by the AACC Academy and AACC'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. AACC'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.