What are the steps to confirm type 2 diabetes mellitus when the patient has an elevated hemoglobin A1c?

Confirming Type 2 Diabetes with Hemoglobin A1C of 6.8%

An A1C of 6.8% does NOT meet the diagnostic threshold for diabetes (which requires ≥6.5%), so you must repeat the A1C test or perform a different confirmatory test to establish the diagnosis. 1

Diagnostic Approach

Step 1: Verify the Initial A1C Result

• Ensure the A1C was performed using an NGSP-certified laboratory method standardized to the DCCT assay 1
• Point-of-care A1C devices should not be used for diagnostic purposes due to lack of mandated proficiency testing 1
• If the initial test was not performed in a certified laboratory, repeat it in an appropriate setting 1

Step 2: Confirm the Diagnosis with Repeat Testing

Since the A1C of 6.8% exceeds the diagnostic threshold of ≥6.5%, you have two options for confirmation 1:

Option A: Repeat the A1C test (preferred for consistency)

• Obtain a second A1C measurement from a new blood sample without delay 1
• If the repeat A1C is also ≥6.5%, diabetes is confirmed (e.g., if repeat is 6.8%, 6.6%, or 7.0%, diagnosis is established) 1
• If the repeat A1C falls below 6.5%, the patient does not meet diagnostic criteria and should be monitored closely with repeat testing in 3-6 months 1

Option B: Use a different diagnostic test

• Perform fasting plasma glucose (FPG) or 2-hour oral glucose tolerance test (OGTT) 1
• If either test is above its diagnostic threshold (FPG ≥126 mg/dL or 2-hour PG ≥200 mg/dL), diabetes is confirmed even if the tests are discordant 1
• Both tests from the same sample or two different samples above thresholds confirms diagnosis 1

Step 3: Evaluate for Conditions That May Affect A1C Accuracy

Before finalizing the diagnosis, assess for factors that can falsely elevate or lower A1C independently of glycemia 1:

Conditions requiring plasma glucose criteria instead of A1C:

• Sickle cell disease or other hemoglobinopathies 1
• Pregnancy (second and third trimesters) 1
• Recent blood loss or transfusion 1
• Hemodialysis 1
• Erythropoietin therapy 1
• Glucose-6-phosphate dehydrogenase deficiency 1
• Iron-deficiency anemia 1

If marked discordance exists between A1C and plasma glucose levels:

• Consider hemoglobin variant interference with the A1C assay 1
• Use an assay without interference or rely solely on plasma glucose criteria 1
• African Americans may have A1C levels 0.4% higher than non-Hispanic whites at similar glucose levels 1

Step 4: Handle Discordant Results

If A1C and glucose tests disagree:

• Repeat the test that exceeded the diagnostic threshold 1
• The diagnosis is based on whichever test is confirmed to be abnormal on repeat testing 1
• If A1C is confirmed ≥6.5% on two occasions but FPG remains <126 mg/dL, the patient still has diabetes 1

Critical Pitfalls to Avoid

• Do not diagnose diabetes based on a single A1C measurement unless the patient has clear hyperglycemic symptoms with random glucose ≥200 mg/dL 1
• Do not use point-of-care A1C devices for diagnosis 1
• Do not delay confirmatory testing—it should be performed promptly, not in 3 months 1
• Do not ignore conditions affecting red blood cell turnover, as these make A1C unreliable and require glucose-based diagnosis 1
• Do not assume concordance between tests—A1C and glucose-based tests identify different populations and are imperfectly correlated 1

Special Considerations

• The A1C reflects a weighted average of glucose over approximately 120 days, more heavily influenced by recent exposure 1
• A1C has lower sensitivity than 2-hour glucose testing and may miss up to one-third of diabetes cases compared to FPG criteria 1
• In children and adolescents, the appropriateness of A1C for diagnosis remains unclear as validation studies included only adults 1