A blood test called  hemoglobin A1C (HbA1C) test reveals your average blood sugar (glucose) level over the previous two to three months.

Your blood contains glucose, a form of sugar that is obtained from the food you eat. Glucose provides energy to your cells. The hormone insulin aids in the uptake of glucose by your cells. If you have diabetes, your body either produces insufficient insulin or your cells don't properly utilize it. Because of the inability of glucose to enter your cells, your blood sugar levels increase.

Hemoglobin, a protein found in red blood cells, binds to glucose in your blood. Your hemoglobin will become increasingly glucose-coated as your blood glucose levels rise. The percentage of your red blood cells with hemoglobin coated in glucose is determined by an A1C test.

An A1C test can reveal your three-month average blood glucose level because:

Hemoglobin and glucose remain bound for the duration of the life of the red blood cells.

Red blood cells has about three-month lifespan.

Diabetes-related elevated blood glucose is indicated by high A1C values. Diabetes can lead to major health issues such nerve damage, renal damage, and heart disease. But, you can control your blood sugar levels with treatment and lifestyle modifications.

HbA1C, A1C, glycohemoglobin, glycated hemoglobin, and glycosylated hemoglobin are some of its alternate names.

What is it used for?

An A1C test may be used to screen for or diagnose:

diabetes type 2. Because your body doesn't produce enough insulin to transport blood sugar from your bloodstream into your cells or because your cells stop reacting to insulin, type 2 diabetes causes your blood glucose to become too high.

Prediabetes. Your blood glucose levels are above average but not high enough to be labeled as prediabetes. Healthy nutrition and exercise are two lifestyle modifications that may help postpone or stop the progression of prediabetes to type 2 diabetes.

An A1C test helps monitor your condition and determine how well you've been able to control your blood sugar levels if you have diabetes or prediabetes.

The patient's HbA1C level may also need to be checked by the doctor in order to determine whether or not they can fast during Ramadan. Under some circumstances, fasting during Ramadan could put patient’s health at risk. 

For example, people living with type 2 diabetes who manage with diet and lifestyle only, or who take one diabetes medication that does not increase their risk of hypoglycaemia will have a lower risk during the fast if they are already keeping their average blood sugar level (HbA1c) in a healthy range.