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Cross-checked against published sources on October 8, 2026 (automated, AI-assisted); not reviewed by a licensed clinician. Not medical advice, not for diagnosis or treatment decisions. Always verify with current guidelines and consult a qualified professional. We may be wrong: this page can contain errors. If you spot one, report it and we will check it against current sources and correct it.

Sources checked (4)

American Board of Internal Medicine. ABIM Laboratory Test Reference Ranges - January 2026 (accessed October 8, 2026)
National Library of Medicine (MedlinePlus). A1C test: MedlinePlus Medical Encyclopedia (accessed October 8, 2026)
American Diabetes Association (Diabetes Care). 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes-2025 (PMC11635041) (accessed October 8, 2026)
Clinical Chemistry (Oxford University Press). The National Glycohemoglobin Standardization Program: Over 20 Years of Improving HbA1c Measurement (PMC6693326) (accessed October 8, 2026)

Source policy Medical disclaimer

Glucose

Glycated haemoglobin (HbA1c)

Source-checked · Content last updated 2026-10-07 · 1 min read ·

This is the date the draft was written, not a medical review date.

HbA1c reflects average glycaemia over the preceding 2-3 months (weighted to the most recent weeks) and is used for diagnosis and monitoring of diabetes.

Reference interval

	Conventional (% (NGSP/DCCT))	SI (mmol/mol (IFCC))
Adults	4–5.6 % (NGSP/DCCT)	20–38 mmol/mol (IFCC)

Specimen: Whole blood (EDTA) · Conventional × 10.929 = SI

Causes of high values

Diabetes mellitus (6.5 % / 48 mmol/mol or above per ADA and WHO) and prediabetes (5.7-6.4 % / 39-47 mmol/mol per ADA; WHO and some countries use different lower cut-offs). Falsely high values occur with iron deficiency, splenectomy and vitamin B12 deficiency.

Causes of low values

Falsely low values: haemolytic anaemia, recent blood loss or transfusion, haemoglobin variants in some assays, chronic kidney disease with erythropoietin therapy, and pregnancy. True low values accompany recurrent hypoglycaemia.

Pre-analytical and method notes

Convert with the IFCC-NGSP master equation: HbA1c (mmol/mol) = (NGSP % - 2.15) x 10.929, so the SI value is not a simple multiple of the percentage (the stated factor applies to the slope only); 4.0-5.6 % corresponds to about 20-38 mmol/mol, 6.5 % to 48 mmol/mol. Use only NGSP-certified, standardised assays; haemoglobinopathies and altered red-cell lifespan make HbA1c unreliable, and individual targets vary by guideline and patient.

References

Standards of Care in Diabetes (annual publication in Diabetes Care). American Diabetes Association — Tier 2 (guidelines / primary literature)
Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia: report of a WHO/IDF consultation. World Health Organization (2006) — Tier 1 (standards / international bodies)
Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)

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