Glycated Haemoglobin (HbA1c) – Definition & Values
Glycated haemoglobin (HbA1c) is a blood marker that reflects average blood glucose levels over the past 2 to 3 months and is used to diagnose and monitor diabetes mellitus.
Things worth knowing about "Glycated Haemoglobin"
Glycated haemoglobin (HbA1c) is a blood marker that reflects average blood glucose levels over the past 2 to 3 months and is used to diagnose and monitor diabetes mellitus.
What is Glycated Haemoglobin?
Glycated haemoglobin, commonly referred to as HbA1c or haemoglobin A1c, is a form of the oxygen-carrying protein haemoglobin to which glucose has become attached through a process called glycation. This is a non-enzymatic, spontaneous chemical reaction that occurs continuously in the bloodstream. Because red blood cells have a lifespan of approximately 90 to 120 days, the HbA1c value reflects the average blood glucose concentration over the past 2 to 3 months, making it a reliable long-term indicator of blood sugar control.
Clinical Significance
HbA1c is one of the most important diagnostic tools in diabetology. It is used both for the diagnosis of diabetes mellitus and for the ongoing monitoring of glycaemic control in patients already known to have the condition. Unlike a single fasting blood glucose reading, which reflects only a momentary value, HbA1c provides a comprehensive picture of long-term glucose management.
Reference Values and Thresholds
- Normal range: below 5.7% (below 39 mmol/mol)
- Prediabetes: 5.7% to 6.4% (39–47 mmol/mol)
- Diabetes mellitus: 6.5% or above (48 mmol/mol or above)
- Therapeutic target in known diabetes: generally below 7.0% (53 mmol/mol), individualised per patient
Diagnosis and Measurement
The HbA1c value is determined through a simple blood draw. No fasting is required prior to the test, as the result is not affected by recent food intake. Laboratory analysis is performed using standardised methods such as high-performance liquid chromatography (HPLC). Results are reported either as a percentage (%) or in mmol/mol, in accordance with the recommendations of the International Federation of Clinical Chemistry (IFCC).
Limitations of HbA1c Measurement
In certain circumstances, HbA1c results may be unreliable:
- Haemoglobin variants (e.g. sickle cell disease, thalassaemia) can interfere with accurate measurement.
- Anaemia or increased red blood cell turnover (e.g. after blood transfusions) may affect results.
- During pregnancy, the reliability of HbA1c can be reduced due to changes in red blood cell lifespan.
- Certain medications (e.g. erythropoietin, iron supplements) may influence test outcomes.
Treatment and Therapeutic Goals
The primary aim of diabetes management is to maintain HbA1c within an individually defined target range in order to prevent long-term complications such as cardiovascular disease, chronic kidney disease, neuropathy, and vision loss. Treatment strategies include:
- Lifestyle modifications: balanced nutrition, regular physical activity, and weight management
- Oral antidiabetic agents: such as metformin, SGLT2 inhibitors, and DPP-4 inhibitors
- Insulin therapy: mandatory for type 1 diabetes; used in type 2 diabetes as needed
- Regular medical monitoring: HbA1c is typically measured every 3 months to assess treatment effectiveness
References
- World Health Organization (WHO): Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus. Geneva, 2011.
- American Diabetes Association (ADA): Standards of Medical Care in Diabetes. Diabetes Care, 2024.
- International Federation of Clinical Chemistry (IFCC): IFCC Reference System for Measurement of HbA1c. Clinical Chemistry and Laboratory Medicine, 2002.
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