Blood sugar tests: Understanding your results

Introduction

Blood sugar tests measure how well your body processes sugar (glucose). Some blood sugar tests are used to diagnose prediabetes or diabetes. Others determine how well you're managing your diabetes.

Click on the tabs to the left to learn more about various blood sugar tests and what the results mean.

Fasting blood sugar test

What is a fasting blood sugar test?
A fasting blood sugar test measures the amount of sugar in your blood after you fast for at least eight hours or overnight.

What's normal?
A normal fasting blood sugar result is lower than 100 milligrams of glucose per deciliter of blood (mg/dL).

What level suggests prediabetes?
If your fasting blood sugar level is 100 mg/dL to 125 mg/dL, you have impaired fasting glucose — commonly known as prediabetes. To confirm the diagnosis, your doctor may repeat the fasting blood sugar test several days to a week later.

What level suggests type 1 or type 2 diabetes?
A fasting blood sugar level of 126 mg/dL or higher is consistent with either type 1 or type 2 diabetes when accompanied by classic signs and symptoms of diabetes — increased thirst or hunger, frequent urination, weight loss or blurred vision.

To confirm the diagnosis, your doctor may repeat the fasting blood sugar test on another day. If your test results are 126 mg/dL or higher twice in a row after at least eight hours of fasting, you may have diabetes.

If your blood sugar level is higher than 200 mg/dL and you have signs or symptoms of diabetes, you may be diagnosed with diabetes without a second test for confirmation.

Random blood sugar test

What is a random blood sugar test?
A random blood sugar test measures your blood sugar at any point in time, not necessarily a certain amount of time after a meal, snack or beverage.

What's normal?
A normal random blood sugar result is lower than 100 mg/dL.

What level suggests prediabetes?
If your random blood sugar level is higher than 100 mg/dL but lower than 199 mg/dL, you may have prediabetes.

What level suggests type 1 or type 2 diabetes?
A random blood sugar level of 200 mg/dL or higher suggests either type 1 or type 2 diabetes. Remember, your blood sugar level alone isn't enough to differentiate between type 1 and type 2 diabetes. Your doctor may do other tests to determine which type of diabetes you have.

Oral glucose tolerance test

What is an oral glucose tolerance test?
An oral glucose tolerance test measures your body's response to sugar. First your fasting blood sugar level is measured. Then you drink a sugary solution. Your blood sugar level is measured after one hour and again after two hours. If your blood sugar level rises more than normal, you may have diabetes.

For this test to be accurate, it's important to eat normally and be in good health. Even a cold can affect the results. So can inactivity or certain medications. A modified version of the oral glucose tolerance test, known as a glucose challenge test, is often used to screen pregnant women for gestational diabetes.

What's normal?
A normal blood sugar level after an oral glucose tolerance test is lower than 140 mg/dL.

What level suggests prediabetes?
If your blood sugar level is 140 mg/dL to 199 mg/dL after an oral glucose tolerance test, you may have prediabetes.

What level suggests type 1 or type 2 diabetes?
A blood sugar level of 200 mg/dL or higher two hours after you drink the sugary solution may indicate diabetes. Your doctor may repeat this or other tests to confirm the diagnosis.

Glycated hemoglobin (A1C) test

What is an A1C test?
An A1C test, also known as a glycated hemoglobin test, isn't used for diagnosing prediabetes or diabetes. Instead, it gauges how well you're managing your diabetes.

Unlike a fasting blood glucose test or a daily finger stick, both of which measure your blood sugar level at a given time, the A1C test reflects your average blood sugar level for the past two to three months. Test results show what percentage of your hemoglobin — a protein found in red blood cells — is sugar coated (glycated).

What's normal?
The normal range for people without diabetes is 4 percent to 6 percent. An A1C level lower than 7 percent is a common target for people with diabetes — although your doctor may recommend a level lower than 6 percent if you're pregnant or have other health concerns. An A1C level higher than 7 percent may indicate the need for a change in your diabetes treatment plan.

The normal range for A1C results may vary somewhat among labs. If you consult a new doctor or use a different lab, it's important to consider this possible variation when interpreting your test results.