What does it mean when blood glucose levels are normal but glycated hemoglobin (HbA1c) is elevated?

Normal blood glucose levels with elevated glycated hemoglobin (HbA1c) may be due to: 1) Pathological factors—such as abnormal glucose metabolism or hematologic disorders; and 2) Non-pathological factors. Details are as follows:

Pathological Factors:

1. Abnormal glucose metabolism: Fasting and postprandial blood glucose reflect short-term glucose levels, which are influenced by both the quantity and type of food consumed. In contrast, HbA1c reflects the average blood glucose level over the preceding 2–3 months. Thus, normal fasting and postprandial glucose values alongside elevated HbA1c may indicate underlying glucose metabolism abnormalities. Initial management includes dietary and exercise interventions. If HbA1c remains elevated despite lifestyle modifications, further diagnostic testing—including oral glucose tolerance test (OGTT), insulin release test, and C-peptide release test—is warranted.

2. Hematologic disorders: Patients with hemoglobinopathies may yield unreliable HbA1c measurements. Therefore, recurrent elevations in HbA1c should prompt evaluation for underlying hematologic disease.

Non-Pathological Factor: HbA1c levels tend to increase progressively with advancing age.