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Hemoglobin A1c

HbA1c shows what your average blood sugar has been over the past two to three months.

What is Hemoglobin A1c?

HbA1c measures the fraction of your haemoglobin that has glucose attached to it. That coating builds up slowly and stays put for the life of the red blood cell. HbA1c therefore reflects your average blood glucose over roughly the previous two to three months, weighted toward the most recent weeks. Unlike fasting glucose, HbA1c is not a snapshot. Whether you ate breakfast, slept badly, or were stressed on the morning of the draw does not change the result. That stability is what makes it the most reliable single marker for how your glucose regulation is running structurally. Always read it alongside fasting glucose, triglycerides, and the triglyceride/HDL ratio.

Why is Hemoglobin A1c relevant?

HbA1c is one of the best-validated markers in preventive medicine. It tracks the slow, silent drift toward insulin resistance — often years before fasting glucose or any symptoms appear. At that early stage, glucose regulation is still reversible with lifestyle change. A gradually rising HbA1c is an early warning you can act on. Persistently higher values are tied to an increased risk of type 2 diabetes and cardiovascular damage. That damage starts accumulating before any diagnostic threshold is crossed. Treat HbA1c as an early trend to act on, not a self-diagnosis — a value near a cut-off is a reason to retest and evaluate lifestyle, not to panic.

Hemoglobin A1c high or low — what it means

Read HbA1c as a trend across multiple measurements. A gradual upward drift over one to two years tells you more than any single reading. When HbA1c rises alongside high triglycerides or a high triglyceride/HDL ratio, the metabolic picture is consistent and worth addressing. A raised HbA1c almost always reflects glucose regulation under strain: excess abdominal fat, too little movement, poor sleep, refined carbohydrates, and chronic stress. The levers: lose excess weight, cut sugar and processed carbs, move regularly (both resistance training and endurance), and prioritise sleep. Changes are measurable after two to three months. In endurance athletes, HbA1c can run slightly higher than expected because training extends red-cell lifespan.

Hemoglobin A1c reference ranges

NormalAbout < 40 mmol/mol (IFCC). ADA classification.< 5.7 %
PrediabetesAbout 40–47 mmol/mol (IFCC). ADA classification.5.7–6.4 %
DiabetesAbout ≥ 48 mmol/mol (IFCC), confirm on a second test. WHO/ADA threshold.≥ 6.5 %
NHG (Dutch primary care)In the Netherlands diabetes is diagnosed on repeated fasting glucose (≥ 7.0 mmol/L on two days), not on HbA1c; HbA1c is used to monitor control.fasting glucose ≥ 7.0 mmol/L mmol/L

General reference bands (ADA), not a diagnosis on their own. Cut-offs vary between laboratories and guidelines; Dutch labs usually report in mmol/mol (IFCC). The NHG standard diagnoses diabetes on fasting glucose, not HbA1c.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.

Read about our scientific approach →Read the guide: Nutrition →

Frequently asked questions

What is a normal HbA1c level?

Under the common (ADA) classification, below 5.7% — about 40 mmol/mol on the IFCC scale used by Dutch labs — is considered normal. Between 5.7 and 6.4% (roughly 40–47 mmol/mol) is the prediabetes range, and 6.5% or higher (about 48 mmol/mol), confirmed on a second test, is the WHO/ADA threshold for diabetes. These cut-offs vary between labs and guidelines.

What does a high HbA1c mean?

A raised HbA1c means your average blood sugar over the past two to three months was higher. It usually points to glucose regulation under strain: excess abdominal fat, low physical activity, poor sleep, a diet heavy in refined carbohydrates, and chronic stress. Sustained higher values are tied to an increased risk of type 2 diabetes and cardiovascular damage — and that risk rises in a graded way across the whole range, including below the diabetes cut-off.

When is an HbA1c level concerning and what can you do about it?

What matters most is a creeping trend: a drift from, say, 5.4% to 5.7% over a year is more telling than any single reading. If you sit in or near the prediabetes range (5.7–6.4%), confirm it with a repeat test and discuss it with a clinician. The levers are largely within your control: lose excess weight, cut sugar and refined carbohydrates, exercise regularly (resistance plus endurance training), prioritise sleep, and manage stress. Effects are measurable after two to three months. Note: in endurance athletes HbA1c can run slightly high, and anemia or kidney disease can distort the result.

Does a Dutch GP diagnose diabetes from HbA1c?

No. The NHG standard makes the diagnosis on a repeated fasting glucose (≥ 7.0 mmol/L on two separate days), not on HbA1c. HbA1c is mainly used to monitor control once diabetes is known. So an HbA1c near a cut-off is a reason to retest and check a fasting glucose, not a verdict.

Related biomarkers

Glucose (Fasting)
Fasting glucose is your blood sugar after a night without eating and shows how well your body processes glucose.
Triglycerides
Triglycerides are a blood fat that responds strongly to diet and alcohol and reflects your metabolic health.
Triglycerides / HDL Ratio
The triglyceride/HDL ratio divides your triglycerides by your HDL and gives a quick read on your insulin sensitivity.

Hemoglobin A1c is one of the biomarkers in the Optimize blood test. Book a blood draw at any of 238+ partner labs in the Netherlands, or upload your existing results in the app.

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