Diabetes Basics
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Dear Diabetes: What Is a Fasting Blood Glucose Test?

The basics of testing fasting blood glucose levels

Dear Diabetes: What is fasting blood glucose testing?

In people living with diabetes, the body stops producing or is unable to properly use insulin, a hormone that helps to move glucose from the bloodstream into the cells, where glucose is then converted into energy. People with type 1 diabetes and some people with type 2 diabetes take some form of therapeutic insulin to help their bodies with blood glucose uptake. (Read more about insulin here.)

Therapeutic insulin serves two purposes: to help with the blood sugar spikes after the meal and to control blood sugar levels between meals and overnight.

What is a fasting blood glucose test?

A person’s basal insulin dose is adjusted to meet a recommended fasting plasma glucose target. Fasting plasma glucose is measured with a blood test after not eating for at least eight hours. (When a person self-monitors blood glucose, this is usually the measurement in the morning before breakfast.) The fasting plasma glucose target range is determined by a doctor based on a person’s health status. The American Diabetes Association recommends a fasting plasma glucose target between 80 to 130 mg/dL for many non-pregnant adults with diabetes.

Fasting blood glucose vs. fasting plasma glucose

You may see references to both “plasma glucose” and “blood glucose”; there is a difference. Plasma has a higher water content than whole blood and fasting plasma readings can be 10–12 percent higher than fasting blood glucose readings. Most blood glucose monitors automatically convert blood glucose values into plasma glucose values. Check with your healthcare team to determine which values your meter reads.

“It’s important that your blood glucose levels remain stable and on target throughout the day, and overnight, while you’re sleeping,” says Gary Scheiner, MS, CDE,* and the author of Think Like a Pancreas. “If you’re taking basal insulin and not achieving the fasting blood sugar levels you want, or are experiencing frequent high blood sugar (hyperglycemia) or low blood sugar (hypoglycemia), it’s important to work with your healthcare team to fine-tune your program.”

* “Certified Diabetes Educator” and “CDE” are certification marks owned and registered by the National Certification Board for Diabetes Educators (NCBDE). NCBDE is not affiliated in any way with Sanofi US. NCBDE does not sponsor or endorse any diabetes-related products or services.

© 2015 The DX: The Diabetes Experience

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