Meaning
HbA1c refers to glycated hemoglobin, a form of hemoglobin that is chemically linked to glucose. It is used as a diagnostic and monitoring marker for diabetes mellitus.
When glucose circulates in the bloodstream, a portion of it binds irreversibly to hemoglobin in red blood cells. The higher the blood glucose level, the greater the percentage of glycated hemoglobin.
What It Measures
- Reflects the average blood glucose level over the previous 2–3 months.
- Based on the lifespan of red blood cells (approximately 120 days).
- Expressed as a percentage of total hemoglobin.
Diagnostic Criteria
According to international and Indian diabetes guidelines:
- Normal: Below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher (confirmed on repeat testing)
For individuals with diabetes, treatment targets are usually around 6.5% to 7%, depending on age, comorbidities, and risk of hypoglycemia.
Clinical Significance
Diagnosis of Diabetes
- HbA1c ≥ 6.5% is one of the accepted criteria for diagnosing diabetes mellitus.
Monitoring Glycemic Control
- Used to assess long-term glucose control.
- Helps evaluate effectiveness of treatment (diet, oral drugs, insulin).
Risk Prediction
- Higher HbA1c levels are associated with increased risk of complications such as:
- Diabetic retinopathy
- Nephropathy
- Neuropathy
- Cardiovascular disease
Advantages
- Does not require fasting.
- Reflects long-term glucose exposure rather than single-point readings.
- Less affected by short-term stress or illness compared to random glucose tests.
Limitations
HbA1c values may be unreliable in conditions such as:
- Anemia
- Hemoglobinopathies
- Chronic kidney disease
- Recent blood transfusion
- Conditions affecting red blood cell lifespan
In such cases, alternative tests like fasting plasma glucose or continuous glucose monitoring may be preferred.
Importance in Public Health
- Widely used in screening programs for diabetes.
- Important in countries like India with a high burden of type 2 diabetes.
- Supports early detection and prevention of long-term complications.
Conclusion
HbA1c is a crucial biomarker for diagnosing and monitoring diabetes. By reflecting average blood glucose levels over time, it enables clinicians to assess long-term glycemic control and reduce the risk of chronic complications.
