HbA1c
Long-term blood sugar average over 2–3 months
Also known as
Definition
HbA1c (glycated hemoglobin) reflects the average blood glucose level over the preceding two to three months, as glucose binds reversibly to hemoglobin in red blood cells. It is the central diagnostic and monitoring marker for type 2 diabetes mellitus and prediabetes, and is also used in biohacking to track insulin sensitivity and the impact of dietary interventions.
| Parameter | Value |
|---|---|
| Unit | % (mmol/mol) |
| Reference Range | < 5.7% (normal) | 5.7–6.4% (prediabetes) | ≥ 6.5% (diabetes, ADA criteria) |
| Optimal Range (lab2go) | < 5.4% (lab2go Optimum Zone) |
HbA1c is reported in % (NGSP/DCCT standard) in the US. Internationally also in mmol/mol (IFCC). Conversion: IFCC (mmol/mol) = (NGSP % − 2.15) × 10.929. Example: 5.7% ≈ 39 mmol/mol.
↓ What a low value means
HbA1c < 4.5% can indicate hypoglycemia tendency, hemolytic anemia (shorter red cell lifespan falsely lowers HbA1c), iron-deficiency anemia, or very low-carbohydrate diet. Extremely low values below 4.0% should be clarified with fasting glucose and CGM.
↑ What a high value means
HbA1c 5.7–6.4% = prediabetes (elevated risk of type 2 diabetes and cardiovascular disease). HbA1c ≥ 6.5% = diabetes mellitus (ADA diagnostic criterion; confirm with repeat measurement). In diabetes therapy: HbA1c > 7.0% = inadequate control. Elevated values correlate with micro- and macroangiopathy, neuropathy, retinopathy.
✓ How to optimize this marker
Diet: reduce rapidly absorbed carbohydrates (sugar, white flour), Mediterranean or low-carb diet. Exercise: 150 min/week moderate aerobic + strength training demonstrably improve insulin sensitivity. Weight loss: even 5% body weight reduction lowers HbA1c. Intermittent fasting (16:8) shows positive effects in studies. Optimize sleep duration (< 6 hours increases insulin resistance).
When to test
No fasting required. Diabetes screening: initial measurement from age 45, or earlier with risk factors (BMI > 25, family history, hypertension). Follow-up in diabetes: every 3 months. In prediabetes: every 6–12 months. Iron-deficiency anemia and hemolytic conditions can falsify the value.
Frequently asked questions
Can HbA1c be falsely low or falsely high? +
Yes. Falsely low: hemolytic anemia, blood loss (shorter red cell lifespan). Falsely high: iron-deficiency anemia (longer red cell lifespan), kidney insufficiency. When HbA1c and fasting glucose do not match, CGM or fructosamine is helpful.
Can a low-carb diet normalize my HbA1c? +
Yes. Low-carbohydrate diets can significantly lower HbA1c in prediabetes and type 2 diabetes (by 0.5–1.5 percentage points). With insulin or sulfonylurea medications, hypoglycemia risk increases — inform your physician.
What is the advantage of HbA1c over fasting glucose? +
HbA1c integrates blood glucose over 2–3 months and is not distorted by day-to-day fluctuations. Fasting glucose only shows the momentary value. HbA1c is less affected by the stress of blood draw and does not require fasting.
Sources
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.