Haemoglobin A1c (HbA1c) Test
The haemoglobin A1c (HbA1c) test measures glycated haemoglobin in whole blood, reflecting average blood glucose over the preceding two to three months. It is the standard test for diagnosing type 2 diabetes and prediabetes and for monitoring long-term glycaemic control, and it does not require fasting.
1
Biomarkers
Blood (whole blood)
Sample
1–3 business days
Turnaround
No
Fasting
What is the HbA1c test?
The Haemoglobin A1c Test measures glycated haemoglobin, providing an integrated index of average blood glucose over the preceding two to three months. It is the standard test for diagnosing type 2 diabetes and prediabetes and for monitoring long-term glycaemic control without the need for fasting. Within diabetes assessment, HbA1c complements fasting glucose and the oral glucose tolerance test, offering the advantage of reflecting chronic rather than instantaneous glycaemia and being unaffected by recent meals. It is used to establish a diagnosis against standardised thresholds, to set and track individualised treatment targets, and to gauge cardiovascular and microvascular risk. Its key limitation is dependence on a normal red-cell lifespan: anaemias, haemoglobinopathies, recent transfusion, pregnancy, and conditions altering erythrocyte turnover can distort the result, in which case glucose-based testing or fructosamine is preferred.
What does the HbA1c test measure?
Haemoglobin A1c is formed by the non-enzymatic glycation of the N-terminal valine of the haemoglobin beta chain, with the degree of glycation proportional to the ambient glucose concentration over the lifespan of the red cell. Because erythrocytes circulate for approximately 120 days, HbA1c reflects average glycaemia over the preceding 8–12 weeks, weighted toward the most recent weeks. It is reported in NGSP percentage units and in IFCC mmol/mol units, with standardised assay traceability.
HbA1c is the principal marker for diagnosing and monitoring type 2 diabetes and prediabetes and for assessing long-term glycaemic control, with treatment targets individualised to the patient. It does not require fasting and is less affected by day-to-day fluctuation than a single glucose measurement. Its reliability depends on a normal red-cell lifespan, so conditions altering erythrocyte turnover or haemoglobin structure can render it inaccurate, and alternative measures such as fructosamine may then be needed.
Why is the HbA1c test ordered?
- Diagnosis of type 2 diabetes or prediabetes against standardised thresholds in at-risk or symptomatic patients
- Monitoring of long-term glycaemic control in established diabetes, tracked against individualised targets
- Screening of asymptomatic adults with risk factors — obesity, hypertension, dyslipidaemia, or family history — as part of metabolic assessment
- Assessment of glycaemic status where fasting is impractical, given HbA1c does not require fasting
- Evaluation of cardiovascular and microvascular risk in patients with metabolic syndrome or established diabetes
- Monitoring response to lifestyle or pharmacological intervention over a two-to-three-month horizon
- Reassessment where a single glucose value is discordant with the clinical picture and an integrated measure of glycaemia is wanted
Sample collection and turnaround
Sample type
Blood (whole blood)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
1–3 business days
Collection notes
Collect into the specified EDTA whole-blood tube; fasting is not required and the sample can be drawn at any time of day. Document any anaemia, recent transfusion, pregnancy, or known haemoglobinopathy that may affect interpretation.
Specimen requirements
Whole blood in EDTA per Quest protocol; minimum volume as specified by the laboratory. Mix gently to prevent clotting; specimen stable refrigerated within the laboratory's stated window. Follow Quest transport guidelines.
What can affect HbA1c results?
Conditions that shorten red-cell lifespan (haemolysis, recent blood loss) lower HbA1c, while those that prolong it (iron-deficiency anaemia, B12/folate deficiency) can raise it, independent of glycaemia.
Variant haemoglobins (e.g. HbS, HbC, HbE) and elevated HbF can interfere with certain assays, producing falsely high or low results; a method unaffected by the relevant variant should be used.
Transfused cells and acute blood loss change the red-cell population and its glycation history, transiently distorting HbA1c so that it no longer reflects the patient's own glycaemia.
Increased red-cell turnover and physiological changes in pregnancy lower HbA1c, so it is not recommended for diagnosing gestational diabetes, where glucose-based testing is used.
Altered red-cell survival and carbamylation of haemoglobin in renal failure can affect HbA1c and certain assays, complicating interpretation in advanced kidney disease.
Iron deficiency prolongs red-cell survival and alters glycation, modestly raising HbA1c independent of glucose; correcting the deficiency can lower the measured value.
What do HbA1c results mean?
Elevated
An HbA1c of 6.5% (48 mmol/mol) or above on a standardised assay is consistent with diabetes, and 5.7–6.4% (39–47 mmol/mol) with prediabetes. In established diabetes, a rising HbA1c indicates worsening control. Confirm with a repeat or a glucose-based test where the result is unexpected or red-cell turnover may be altered.
Normal
An HbA1c below 5.7% (39 mmol/mol) is within the non-diabetic range. A normal value does not exclude diabetes if a haemoglobinopathy or altered red-cell turnover is distorting the result, in which case glucose-based testing should be used.
Reduced
A low or falling HbA1c may reflect improved glycaemic control or, alternatively, conditions that shorten red-cell lifespan such as haemolysis or recent blood loss. In patients on glucose-lowering therapy, a low value may also raise the question of hypoglycaemia risk.
Note: HbA1c assumes a normal red-cell lifespan, so anaemias, haemoglobin variants, recent transfusion, pregnancy, and advanced renal disease can all distort it. It reflects average glycaemia and can mask wide glucose excursions or hypoglycaemia. Where HbA1c is unreliable, fasting glucose, an oral glucose tolerance test, or fructosamine should be used instead.
Frequently asked questions
It measures glycated haemoglobin, which reflects average blood glucose over the preceding two to three months. It is the standard test for diagnosing and monitoring diabetes and prediabetes.
How to access the HbA1c test
The HbA1c reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: June 2, 2026
Last reviewed: June 2, 2026
- American Diabetes Association. Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes. Diabetes Care. (2022)
- Nathan DM, et al. Translating the A1C assay into estimated average glucose values. Diabetes Care. (2008)
- Little RR, et al. Standardization of HbA1c measurement: the NGSP perspective. Clin Chem Lab Med. (2013)
- Cavagnolli G, et al. Effect of ethnicity on HbA1c levels in individuals without diabetes: systematic review and meta-analysis. PLoS One. (2017)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.