What Does Your HbA1c Mean?

Hemoglobin A1c (HbA1c) is the share of the haemoglobin in your red blood cells that has glucose attached to it. Red cells live about three months, and the more glucose in your blood over that time, the more haemoglobin gets glycated, so HbA1c reflects your average blood sugar over the past two to three months. It needs no fasting, which makes it a convenient test for diagnosing prediabetes and diabetes.

This article is general information, not medical advice.

The Thresholds

The American Diabetes Association’s (ADA) Standards of Care use:

HbA1c (NGSP, %)	IFCC (mmol/mol)	Meaning
Under 5.7%	Under 39	Normal
5.7% to 6.4%	39 to 47	Prediabetes
6.5% or more	48 or more	Diabetes

A diagnosis normally needs two abnormal results, either the same test repeated or two different tests, such as HbA1c and fasting plasma glucose, unless symptoms make it clear. The percentages are on the NGSP scale, standardised to the US Diabetes Control and Complications Trial; many countries report in mmol/mol on the IFCC scale instead.

When HbA1c Misleads

Because HbA1c depends on how long red cells live, anything that changes red cell turnover changes the result without a change in glucose. The ADA lists:

• Falsely low: recent blood loss or transfusion, haemolysis, some haemoglobin variants, pregnancy (second and third trimesters), and treatment with erythropoietin.
• Falsely high or unreliable: iron deficiency in some cases, and some haemoglobin variants.
• Kidney disease and HIV treatment can also make HbA1c less reliable.

In those situations, plasma glucose tests are used instead.

HbA1c and Fasting Glucose

Fasting plasma glucose is a snapshot after at least 8 hours without food: under 100 mg/dL (5.6 mmol/L) is normal, 100 to 125 mg/dL is prediabetes, and 126 mg/dL (7.0 mmol/L) or more diabetes. The two measure different things, so they don’t always agree; each catches some people the other misses.

Lowering It

Weight loss, physical activity, and diet changes lower HbA1c in prediabetes, and for people with diabetes, medicines too. Because it averages three months, retest no sooner than about three months after a change.

Following It in Kaizora

Hemoglobin A1c (NGSP) and Fasting Plasma Glucose are lab results on Labs. The ADA’s prediabetes and diabetes thresholds come as default reference ranges for both, so a result in either range is flagged, and the lab’s own printed range is kept with each result too. The Kaizora Longevity Score’s metabolic labs component scores HbA1c or fasting glucose with the American Heart Association’s Life’s Essential 8 points; without a diabetes status in Kaizora, a high value is scored as diabetic.

The Short Version

• HbA1c reflects average blood sugar over two to three months.
• Under 5.7% is normal; 5.7% to 6.4% prediabetes; 6.5% or more diabetes.
• Blood loss, anaemia, pregnancy, and some haemoglobin variants can make it misleading.

Sources

• American Diabetes Association Professional Practice Committee, “2. Diagnosis and classification of diabetes: Standards of Care in Diabetes—2025,” Diabetes Care 48, Supplement 1 (2025): S27–S49. doi:10.2337/dc25-S002