A1c Interpretation

A1C is a long-range glycemic signal, not a current glucose reading. Interpret it in a sequence: first decide whether the assay and the patient’s red-cell biology make the value trustworthy; then apply Canadian diagnostic thresholds; compare it with plasma glucose, self-monitoring, or CGM data; and finally choose an individualized target. This prevents two common errors—diagnosing from an unconfirmed result and intensifying treatment in response to an A1C that does not represent the patient’s actual glycemia. An isolated abnormal A1C does not diagnose diabetes in an asymptomatic patient. If the patient has classic hyperglycemic symptoms or is acutely ill, prioritize plasma glucose and assessment for ketones and metabolic decompensation rather than waiting for a slow-moving marker. The clinical question is not simply whether the A1C is high; it is whether the number is valid, what category it represents, and what action the patient’s current risk requires.