Diagnosis

The American Diabetes Association (ADA) recommends that diabetes screening for most adults begin at age 45. The ADA advises diabetes screening before age 45 if you're overweight and have additional risk factors for prediabetes or type 2 diabetes.

There are several blood tests for prediabetes.

Glycated hemoglobin (A1C) test

This test shows your average blood sugar level for the past three months. The test measures the percentage of blood sugar attached to the oxygen-carrying protein in red blood cells called hemoglobin. The higher your blood sugar levels, the more hemoglobin you'll have with sugar attached.

In general:

• An A1C level below 5.7% is considered normal
• An A1C level between 5.7% and 6.4% is considered prediabetes
• An A1C level of 6.5% or higher on two separate tests indicates type 2 diabetes

Certain conditions can make the A1C test inaccurate — such as if you're pregnant or have an uncommon form of hemoglobin.

Fasting blood sugar test

A blood sample is taken after you fast for at least eight hours or overnight.

In general:

• A fasting blood sugar level below 100 milligrams per deciliter (mg/dL) — 5.6 millimoles per liter (mmol/L) — is considered normal.
• A fasting blood sugar level from 100 to 125 mg/dL (5.6 to 7.0 mmol/L) is considered prediabetes. This result is sometimes called impaired fasting glucose.
• A fasting blood sugar level of 126 mg/dL (7.0 mmol/L) or higher indicates type 2 diabetes.

Oral glucose tolerance test

This test is usually used to diagnose diabetes only during pregnancy. A blood sample is taken after you fast for at least eight hours or overnight. Then you'll drink a sugary solution, and your blood sugar level will be measured again after two hours.

In general:

• A blood sugar level less than 140 mg/dL (7.8 mmol/L) is considered normal.
• A blood sugar level from 140 to 199 mg/dL (7.8 to 11.0 mmol/L) is considered prediabetes. This is sometimes referred to as impaired glucose tolerance.
• A blood sugar level of 200 mg/dL (11.1 mmol/L) or higher indicates type 2 diabetes.

If you have prediabetes, your doctor will typically check your blood sugar levels at least once a year.

Children and prediabetes testing

Type 2 diabetes is becoming more common in children and adolescents, likely due to the rise in childhood obesity. The ADA recommends prediabetes testing for children who are overweight or obese and who have one or more other risk factors for type 2 diabetes.

These other risk factors include:

• Family history of type 2 diabetes.
• Race. Children who are African American, Hispanic, Native American, Asian American and Pacific Islander are at higher risk.
• Low birth weight.
• Being born to a mother who had gestational diabetes.

The ranges of blood sugar level considered normal, prediabetic and diabetic are the same for children and adults.

Children who have prediabetes should be tested annually for type 2 diabetes — or more often if the child experiences a change in weight or develops signs or symptoms of diabetes, such as increased thirst, increased urination, fatigue or blurred vision.