Hemoglobin A1C: What Your Result Says About Three Months of Blood Sugar

Your A1C result came back, and you are not sure if the number is good, borderline, or a problem. Maybe your clinician said "prediabetes" and you want to know what that means. This guide explains what the A1C test measures, the cut points clinicians use in Canada and the US, and when the result may not tell the full story.

What A1C measures

Sugar (glucose) in your blood sticks to hemoglobin, the protein inside red blood cells. The A1C test measures the percentage of hemoglobin that has sugar attached [1].

Red blood cells live for about 3 months. So A1C gives a weighted average of your blood sugar over the past 2 to 3 months, with the most recent weeks counting the most [1]. That is why one sweet meal does not change it, and why you do not need to fast.

You may see A1C called HbA1c or glycated hemoglobin. Some labs also report it in millimoles per mole (mmol/mol). An A1C of 6.5 percent equals 48 mmol/mol.

A1C and average glucose

Some reports also show an "estimated average glucose." This turns your A1C into a glucose number [5].

• A1C 6 percent is about 7.0 mmol/L (126 mg/dL).
• A1C 7 percent is about 8.6 mmol/L (154 mg/dL).
• A1C 8 percent is about 10.2 mmol/L (183 mg/dL).

What your doctor looks at

The diagnostic cut points

The American Diabetes Association (ADA) uses these A1C ranges [2]:

• Normal: below 5.7 percent.
• Prediabetes: 5.7 to 6.4 percent.
• Diabetes: 6.5 percent or higher.

Diabetes Canada uses the same cut point for diabetes, 6.5 percent or higher. But it defines prediabetes by A1C as 6.0 to 6.4 percent [3]. So a result of 5.8 percent may be called prediabetes in the US but not in Canada. The risk is real either way. Higher numbers within the normal and prediabetes ranges mean a higher chance of developing diabetes later.

Confirming a diagnosis

One high A1C is usually not enough. Both bodies ask for a second test to confirm diabetes in a person without clear symptoms [2][3]. The second test can be another A1C or a fasting plasma glucose. Diabetes Canada also accepts one A1C of 6.5 percent or higher together with a fasting glucose of 7.0 mmol/L or higher on the same day [4].

If you have classic symptoms, such as strong thirst, passing a lot of urine, and weight loss, plus a very high random glucose, one test may be enough.

Labs must use a standardized method for diagnosis. Point-of-care A1C devices in a clinic are not meant to diagnose diabetes [1].

When A1C may mislead

A1C depends on how long your red blood cells live. Anything that changes that can make the result too high or too low [1][3].

• Iron deficiency anemia can push A1C up.
• Recent blood loss, a transfusion, or hemolysis (red cells breaking down early) can push it down.
• Advanced kidney disease and liver disease can affect it.
• Pregnancy lowers A1C, so it is not used to diagnose gestational diabetes.
• Some inherited hemoglobin variants, such as sickle cell trait, can interfere with some test methods.

A1C is also not the right test to diagnose type 1 diabetes, which can come on fast [1]. In these situations, clinicians use glucose tests instead.

Targets if you already have diabetes

For many adults with diabetes, both the ADA and Diabetes Canada suggest an A1C target of about 7 percent or lower. Targets can be lower or higher depending on age, other health problems, risk of low blood sugar, and personal goals. Your clinician and you set this together.

How often A1C is checked

If you have diabetes, A1C is usually checked every 3 to 6 months. Diabetes Canada suggests about every 3 months when treatment is being adjusted [3].

For screening, Diabetes Canada suggests testing at least every 3 years from age 40, and earlier or more often if you have risk factors [4]. US screening advice from the US Preventive Services Task Force focuses on adults 35 to 70 who have overweight or obesity.

Questions to ask your clinician

• Is my A1C in the normal, prediabetes, or diabetes range by the guideline you use?
• Do I need a repeat A1C or a fasting glucose to confirm this?
• Could anemia, kidney disease, or anything else affect my result?
• What is my personal A1C target, and why?
• How often should I have this test?
• If I have prediabetes, what programs or changes have the best evidence for me?

When to get care quickly

Go to the emergency department or call 911 if you have any of these:

• Very high glucose readings with vomiting, stomach pain, deep or fast breathing, or a fruity smell on the breath.
• Confusion, severe drowsiness, or fainting.
• Signs of very low blood sugar, such as shaking, sweating, and confusion, that do not improve after you take sugar.

Bottom line

A1C is a simple blood test that shows your average blood sugar over about 3 months. A result of 6.5 percent or higher, confirmed on a second test, meets the diabetes cut point in both Canada and the US. Prediabetes starts at 5.7 percent in the US and 6.0 percent in Canada. Some health conditions can make A1C less accurate, so your clinician may confirm it with a glucose test.

Primary AI can show you the guideline and study sources behind this topic in plain language, so you can bring better questions to your appointment.