HbA1c Interpreter

Glucose-lowering medications (metformin, GLP-1 agonists, SGLT2 inhibitors, insulin) directly affect HbA1c by lowering blood glucose. Your unmedicated A1c would be higher than shown.

Corticosteroids (prednisone, dexamethasone) raise blood glucose and can elevate A1c independent of underlying metabolic health.

Conditions that affect red blood cell turnover (anemia, recent blood loss or transfusion, hemoglobinopathies) can distort A1c results in either direction without reflecting actual glucose control. Fasting glucose and fructosamine are alternative markers in these cases.

If any of these apply to you, discuss A1c interpretation with your healthcare provider for proper context.

Formula

HbA1c reflects the percentage of hemoglobin molecules glycated by glucose over the prior 2-3 months — the lifespan of a red blood cell. Estimated average glucose (eAG) is derived via the ADAG formula: eAG (mg/dL) = 28.7 × A1c − 46.7.

Classification

Optimal: below 5.0%. Healthy range: 5.0-5.69%. Elevated (prediabetes range): 5.7-6.49%. Concerning (diabetes threshold): 6.5% and above. These align with American Diabetes Association cutoffs; we use 'optimal' as a stricter target than the standard 'normal' range.

Known Limitations

HbA1c reflects average glucose, not variability or post-meal spikes. Two people with the same A1c can have very different glucose patterns. Conditions that shorten or extend red blood cell lifespan (anemia, recent transfusion, hemoglobinopathies, pregnancy) distort the reading. For early insulin resistance detection, fasting insulin and HOMA-IR detect problems months to years before A1c moves.

Sources

American Diabetes Association Standards of Care. Nathan DM et al., ADAG study. Translating the A1C assay into estimated average glucose values. Diabetes Care, 2008.