Health Measurements: Blood Glucose

What is it?

A blood glucose test measures the amount of a type of sugar, called glucose, in your blood. Glucose comes from carbohydrate foods. It is the main source of energy used by the body. Insulin is a hormone that helps your body's cells use the glucose. Insulin is produced in the pancreas and released into the blood when the amount of glucose in the blood rises.

Normally, your blood glucose levels increase slightly after you eat. This increase causes your pancreas to release insulin so that your blood glucose levels do not get too high. Blood glucose levels that remain high over time can damage your eyes, kidneys, nerves, and blood vessels.

How is it measured?

A fasting blood glucose test measures blood glucose after you have not eaten for at least 8 hours. It often is the first test done to check for diabetes.

Hemoglobin A1C is the average blood glucose level over previous six to 12 week period. It is an important blood test used to provide an average of your blood sugar control. Hemoglobin is a substance within red blood cells that carries oxygen throughout your body. When your blood sugar is out of control (meaning that your blood sugar is too high), sugar builds up in your blood and combines with your hemoglobin, becoming "glycated." Therefore, the average amount of sugar in your blood can be determined by measuring a Hemoglobin A1C level. With recent changes in your lab's reporting standard, this number may also be referred to as eAG (estimated average glucose).

If your glucose levels have been high over recent weeks, your Hemoglobin A1C test will be higher. The amount of Hemoglobin A1C will reflect the last several weeks of blood sugar levels, typically encompassing a period of 120 days. People with diabetes should have this test every three months to determine whether their blood sugars have reached the target level of control. Those who have their diabetes under good control may be able to wait longer between the blood tests, but experts recommend checking at least 2 times a year.

Why are they included?

Both tests are important to help diagnose, monitor and manage diabetes. Blood glucose tests are done to:

• Check for diabetes.
• Monitor treatment of diabetes.
• Check for diabetes that occurs during pregnancy (gestational diabetes).

Diagnosing Diabetes

Fasting Blood Sugars:
Normal: less than 100
Pre-diabetes: 100 to 125
Diabetes: 126 or more than two occasions
Normal HemoglobinA1c: 4 to 6 (or eAG of 125 or less)

Target Levels for Good Diabetes Control:
Pre-meal blood sugars: 70 to 130
After-meal blood sugars: less than 180
HemoglobinA1c: less than 7 (or eAG less than 154)

Additional Resources

Special Diets: Diabetes
Blood Glucose/Diabetes FAQs
National Diabetes Education Program
American Diabetes Association Risk Calculator
Diabetes and Me (CDC)
National Diabetes Information Clearinghouse (NDIC)