From the Guidelines
No, you do not need to repeat an HbA1c test to establish a diagnosis of prediabetes, as a single HbA1c result between 5.7% and 6.4% is sufficient for diagnosing prediabetes. According to the most recent guidelines from the Diabetes Care journal in 2023 1, an HbA1c level of 5.7% to 6.4% is considered diagnostic of prediabetes. The HbA1c test reflects your average blood glucose levels over the past 2-3 months by measuring the percentage of hemoglobin proteins in your blood that are glycated (have glucose attached), making it a reliable indicator of chronic glycemic status without requiring fasting or timed samples.
While repeating the test may be helpful to confirm the diagnosis or monitor progression, it is not required for the initial diagnosis. Alternatively, prediabetes can be diagnosed with a single fasting plasma glucose of 100-125 mg/dL (impaired fasting glucose) or a 2-hour plasma glucose of 140-199 mg/dL during an oral glucose tolerance test (impaired glucose tolerance). Once diagnosed with prediabetes, focus should shift to lifestyle modifications including weight loss if overweight, regular physical activity, and dietary changes to prevent progression to type 2 diabetes.
Key points to consider when diagnosing prediabetes include:
- HbA1c levels between 5.7% and 6.4% are diagnostic of prediabetes 1
- Fasting plasma glucose and oral glucose tolerance tests can also be used to diagnose prediabetes 1
- Lifestyle modifications are crucial in preventing progression to type 2 diabetes
- The HbA1c test is a reliable indicator of chronic glycemic status and does not require fasting or timed samples 1
From the Research
Diagnosis of Prediabetes using HbA1c
- The diagnosis of prediabetes can be made using a fasting glucose level of 100 to 125 mg/dL, a glucose level of 140 to 199 mg/dL measured 2 hours after a 75-g oral glucose load, or a glycated hemoglobin level (HbA1c) of 5.7% to 6.4% or 6.0% to 6.4% 2.
- HbA1c is a standard measure of chronic glycemia for managing diabetes and has been proposed to diagnose diabetes and identify people at risk 3.
- The International Expert Committee recommends that the diagnosis of diabetes be made if HbA1c level is greater than or equal to 6.5% and confirmed with a repeat HbA1c test 4.
Repeat HbA1c Testing
- The International Expert Committee recommends confirming a diagnosis of diabetes with a repeat HbA1c test if the initial result is greater than or equal to 6.5% 4.
- A study used HbA1c to screen for degrees of glucose intolerance amongst patients without known diabetes presenting with acute coronary syndrome, and if the initial result was abnormal (≥6.0%), patients were invited for a repeat HbA1c at 2 weeks 5.
- If an HbA1c test result is discordant with the clinical picture or equivocal, plasma glucose testing should be performed 4.
Practical Considerations
- HbA1c testing has the advantages of greater clinical convenience, preanalytic stability, and assay standardization, but when used as the sole diagnostic criterion for diabetes, it has the potential for systematic error 4.
- Factors that may not be clinically evident impact HbA1c test results and may systematically raise or lower the value relative to the true level of glycemia 4.
- Combining the use of HbA1c and plasma glucose measurements for the diagnosis of diabetes offers the benefits of each test and reduces the risk of systematic bias inherent in HbA1c testing alone 4.