A fasting glucose test is a photograph; HbA1c is the film. It reflects your average blood sugar over roughly three months, which is why it has become the anchor test of diabetes care.
How one test sees three months
Sugar in your blood attaches to haemoglobin in red blood cells, and those cells live for about 120 days. Measuring the percentage of sugar-coated haemoglobin therefore reveals your average sugar across that whole period, and no fasting is required.
Reading your result
Broadly, values below 5.7% are typical, 5.7–6.4% suggests prediabetes, and 6.5% or above supports a diabetes diagnosis. Targets are personal, though. For someone living with diabetes, the right goal depends on age, other conditions, and medicines, which is a conversation, not a chart.
Moving the number
HbA1c responds to steady habits: regular meals, daily movement, sleep, and consistent medicines. Because it moves slowly, retesting every three months is usually right. Testing sooner mostly measures noise.
This guide is general health information, not a diagnosis or treatment recommendation. Your symptoms, examination, reports, medicines, and preferences change the decision.