What HbA1c measures
Sugar in the blood sticks to haemoglobin, the protein inside red blood cells. The HbA1c test measures what percentage of haemoglobin has sugar attached, called glycated haemoglobin. Because red blood cells live for about three months, HbA1c reflects your average blood sugar over roughly the past two to three months. Unlike a single sugar reading, it is not much affected by what you ate yesterday or a stressful morning.
Why doctors order it
Doctors use HbA1c in two main ways. First, to screen for and diagnose diabetes and prediabetes, especially in people with risk factors such as family history, being overweight, high blood pressure, a history of diabetes in pregnancy, or symptoms like excessive thirst and frequent urination. Type 2 diabetes is very common in India and often develops without symptoms for years.
Second, in people who already have diabetes, HbA1c shows how well the treatment plan is working over time. Together with home sugar readings, it helps the doctor decide whether medicines, diet or activity need to change, and it gives a sense of the long-term risk of complications affecting the eyes, kidneys, nerves and heart.
How to prepare
No fasting is needed for HbA1c, and it can be done at any time of day. A small blood sample is taken from a vein, or sometimes by finger-prick with certain machines. However, doctors often order fasting blood sugar or a lipid profile at the same visit, which may need fasting, so follow the instructions you are given. Continue your usual medicines unless your doctor advises otherwise.
What the numbers mean
HbA1c is usually reported as a percentage, and some labs also report it in mmol/mol. Widely used cut-offs for adults are below 5.7% as normal, 5.7% to 6.4% as prediabetes, and 6.5% or above as consistent with diabetes. A diagnosis is usually confirmed with a repeat test or another sugar test, not a single result. Reference ranges and methods may vary slightly between labs, so check your report.
Many reports also show an 'estimated average glucose', which converts HbA1c into a sugar value similar to what you see on a glucometer. This can make the result easier to understand. Remember that it is an average, so it does not show how much your sugar rises and falls during the day.
Targets in diabetes
For many adults with diabetes, doctors aim for an HbA1c around or below 7%, but targets are set individually. Older adults, people with frequent low sugars, heart or kidney disease, or other serious illnesses may have a more relaxed target to keep them safe. Younger people and those planning pregnancy may have a tighter one. Your doctor will explain your personal target. Never change or stop diabetes medicines on your own because of a single result; medicines for diabetes should be taken only on a doctor's prescription.
When the result may be misleading
Because HbA1c depends on red blood cells, conditions that change their lifespan can make results falsely high or low. Your doctor may use other tests, such as fasting and post-meal sugar, a glucose tolerance test or fructosamine, when these apply.
- Anaemia, especially iron deficiency, or recent blood loss or transfusion
- Haemoglobin variants and thalassaemia, which are not rare in India
- Advanced kidney or liver disease
- Pregnancy, where other tests are preferred for diagnosing diabetes
Improving your HbA1c
Lifestyle changes help at every stage, especially in prediabetes, where they can delay or prevent diabetes. Eat balanced meals with plenty of vegetables, dals and whole grains, and smaller portions of rice, chapati, sweets and fried snacks. Walk or exercise regularly, sleep well, avoid tobacco and limit alcohol. Take prescribed medicines exactly as advised and check home sugars if your doctor recommends it.
How often to repeat it
In people with diabetes, HbA1c is commonly checked every three months when treatment is being adjusted or targets are not met, and about every six months when control is stable. People with prediabetes are usually advised to test at least once a year. Those with a normal result but risk factors may repeat it periodically as advised. Consult your doctor to interpret your HbA1c and plan the next test.
See a doctor urgently if
- Very high sugar readings with excessive thirst, frequent urination and weight loss
- Vomiting, abdominal pain, fast breathing or drowsiness in a person with diabetes
- Low sugar symptoms such as sweating, shaking, confusion or fainting
- A foot wound, blister or infection in a person with diabetes that is not healing
Tests that may help
This article is general health information, not medical advice. Do not start, stop or combine medicines on your own — always follow your doctor's prescription and ask your pharmacist if unsure.