Hemoglobin A1c (HbA1c) is a form of hemoglobin that is chemically linked to glucose through a non-enzymatic glycation process, reflecting average blood glucose concentrations over the preceding 2–3 months. It is the primary biomarker used for the diagnosis and long-term monitoring of diabetes mellitus and prediabetes. Results are expressed as a percentage of total hemoglobin or in mmol/mol (IFCC units). Glucose in the bloodstream binds irreversibly to the beta-chain of hemoglobin within red blood cells, forming glycated hemoglobin at a rate proportional to ambient glucose concentration. Because red blood cells have a lifespan of approximately 90–120 days, HbA1c provides a weighted average of blood glucose over that period, with more recent glucose levels contributing more heavily to the result. This process is continuous and does not require fasting, making HbA1c a convenient and stable marker of glycemic exposure.
Hemoglobin A1c (HbA1c) measures the percentage of hemoglobin molecules glycated by glucose over the preceding 2-3 months. It is the clinical gold standard for assessing average glycemic control and is used to diagnose and monitor diabetes mellitus.
An HbA1c of 5.7-6.4% is classified as prediabetes; 6.5% or above is diagnostic for diabetes (per ADA criteria). Upward trends within the normal range may indicate progressive insulin resistance. Conditions that affect red blood cell lifespan (hemolytic anemia, recent transfusion) can alter HbA1c independent of glucose levels.
High-intensity glycolytic exercise acutely increases blood glucose through hepatic glycogenolysis and catecholamine release, but these transient spikes do not meaningfully affect HbA1c. Because HbA1c reflects a multi-month average, it is unaffected by acute training or single-meal glucose fluctuations, making it a stable metabolic benchmark.
Turnaround Time
3 days (up to 10 days)
Fasting Required
No
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