HbA1c shows your average blood sugar over the last two to three months. It measures how much sugar is stuck to haemoglobin in your red blood cells.

A fasting glucose test shows your blood sugar at one moment, after not eating for at least 8 hours. Doctors often use both, and a diagnosis of diabetes is usually confirmed with a second test.

Every lab sets its own normal range, based on its equipment and the people it tests. Always compare your result with the range printed on your own report.

Why this test is done

Screening for prediabetes or type 2 diabetes
Checking how well diabetes is controlled
Symptoms such as thirst, passing a lot of urine or tiredness

What each result means

HbA1c(A1c, glycated haemoglobin)

Average blood sugar over about 3 months.

Typical adult range: Below 5.7% (39 mmol/mol) is normal. 5.7 to 6.4% (39 to 47 mmol/mol) is the prediabetes range. 6.5% (48 mmol/mol) or higher is in the diabetes range.

If high: Above target means sugar has been high on average. People with diabetes usually agree a personal target with their doctor, often around 7% (53 mmol/mol).

If low: Can read falsely low after blood loss, a transfusion or with some types of anaemia.

Fasting glucose(FPG, fasting blood sugar)

Blood sugar after 8 or more hours without food.

Typical adult range: 70 to 99 mg/dL (3.9 to 5.5 mmol/L) is normal. 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is the prediabetes range. 126 mg/dL (7.0 mmol/L) or higher is in the diabetes range.

If high: Can also rise with illness, stress, steroids or if you had eaten.

If low: Below 70 mg/dL (3.9 mmol/L) is low blood sugar; below 54 mg/dL (3.0 mmol/L) is serious, especially if you feel shaky, sweaty or confused.

Before the test

HbA1c needs no fasting. A fasting glucose test needs 8 hours with water only.
Some conditions (sickle cell trait, recent blood loss, pregnancy, kidney disease) can make HbA1c less reliable; your doctor may use other tests.

Questions to ask your doctor

Is this result in the normal, prediabetes or diabetes range for me?
Do I need a second test to confirm it?
What HbA1c target should I aim for?
Could anything make my HbA1c less accurate?

When to get help fast: Seek urgent care for very high sugar with vomiting, deep fast breathing, confusion or drowsiness, or for low sugar that does not improve after eating sugar. In an emergency, call your local emergency number.

Sources

This guide is general information written in plain words. It is not medical advice and has not been reviewed by a doctor for your situation. Read our medical disclaimer.

HbA1c and blood sugar tests: what your numbers mean