HbA1c (Glycated Hemoglobin)

What is it?

HbA1c reflects average blood glucose over roughly the past 2–3 months. It is used to monitor long-term glucose control and to help diagnose diabetes together with other criteria.

Normal ranges

Common ADA-style cutoffs (NGSP %): below 5.7% — usual non-diabetes range; 5.7–6.4% — prediabetes range; 6.5% or higher — diabetes diagnostic threshold when confirmed by repeat testing or clinical context. IFCC mmol/mol ≈ (NGSP − 2.15) × 10.929.

Units: % (NGSP) / mmol/mol (IFCC)

Causes of deviations

Low levels:

Improved glucose control, some hemoglobin variants, hemolysis, recent blood loss — can falsely lower HbA1c; interpretation needs clinical context.

High levels:

Persistent hyperglycemia, prediabetes, diabetes, iron deficiency (can sometimes shift results — lab-dependent).

When to see a doctor

If HbA1c is in prediabetes or diabetes range, or if you have thirst, frequent urination, or unexplained weight change — see a clinician for confirmation and a care plan.

This information is for educational purposes and does not replace medical advice.

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