HbA1c (A1C) test: what it measures and what results mean

The A1C test, also called the HbA1c or glycated haemoglobin test, is one of the most common blood tests in diabetes care. It gives a picture of your blood sugar over several weeks rather than a single moment. This article explains what it shows and what to keep in mind when you read a result.

What does the A1C test measure?

The NIDDK explains that the A1C test is a blood test that reflects your average blood glucose over the past 3 months. It measures how much of your haemoglobin, a protein in red blood cells, has glucose attached to it. Results are given as a percentage. A higher percentage means higher average blood sugar.

Do I need to fast?

No. According to the NIDDK, no fasting is needed for the A1C test, and blood can be drawn at any time of day. This differs from the fasting plasma glucose test and the oral glucose tolerance test, which both need at least 8 hours without food.

What do the numbers mean?

The NIDDK gives these ranges for diagnosis:

• Normal: below 5.7%
• Prediabetes: 5.7% to 6.4%
• Diabetes: 6.5% or above

A diagnosis normally needs confirmation with a second measurement, unless there are clear symptoms of diabetes. The NIDDK also says point-of-care A1C tests done in a doctor's office or clinic should not be used for diagnosis, and that the A1C test should not be used to diagnose type 1 diabetes, gestational diabetes or cystic fibrosis-related diabetes. Only a doctor can interpret your result in light of your health.

When can the result be unreliable?

The NIDDK lists several situations where the A1C result may not reflect true average blood sugar:

• Anaemia: very low iron, such as iron-deficiency anaemia, can cause a falsely high result.
• Changes to red blood cells: recent blood loss, sickle cell disease, treatment with erythropoietin, haemodialysis or a blood transfusion can change A1C levels. Kidney failure and liver disease can also cause false results.
• Haemoglobin variants: people of African, Mediterranean or Southeast Asian descent, or with family members who have sickle cell anaemia or thalassaemia, may carry a haemoglobin variant that makes some A1C tests unreliable. Not all A1C tests are affected.

If any of these apply to you, tell your doctor, who may choose a different test or a different type of A1C test.

How often should people with diabetes have it?

The NIDDK says experts recommend that people with diabetes have an A1C test at least twice a year, and clinicians may test more often if treatment goals are not being met. The NHS describes HbA1c testing every 3 to 6 months for people with type 2 diabetes to check that treatment is working.

What is a good A1C target?

Targets differ from person to person. The NIDDK says keeping A1C below 7% may lower the risk of diabetes complications for some people, but it may not be safe for others, such as people at risk of low blood glucose. A goal of 7% to 8%, or sometimes higher, may suit some people, for example those with limited life expectancy, long-standing diabetes that is hard to control, severe or unnoticed low blood sugar, or advanced complications. Your target should be agreed with your health care professional.

A1C and daily glucose checks

A1C is an average, so it can hide ups and downs during the day. This is why people who use insulin or certain other medicines may also check glucose with a meter or a continuous glucose monitor, as their care team advises.

When to see a doctor

Ask a doctor about testing if you have risk factors for diabetes or signs such as unusual thirst, passing urine often, tiredness or blurred vision. If you already have diabetes, speak to your care team before changing any treatment based on a result.

Seek urgent care for severe symptoms such as trouble breathing, confusion, fainting, or stomach pain with vomiting. In an emergency, call your local emergency number (112 in India, 911 in the United States).

This article is for education only and does not replace advice from your own doctor.