Fasting Plasma Glucose Test: Definition and Overview

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Blood test vials -- Fasting Plasma Glucose Test: Definition and Overview

What is a fasting plasma glucose test?

A fasting plasma glucose test (FPG) is a test that screens for diabetes by measuring the level of glucose in a person’s blood plasma after a period of fasting (not eating). The fasting plasma glucose test is given to nonpregnant adults who are at high risk for diabetes. According to the American Diabetes Association, these “high-risk” candidates for testing include everyone age 45 or older, obese individuals (people who are 120% of their recommended body weight or above), individuals with first-degree relatives (parents, children, or siblings) with diabetes, members of high-risk ethnic groups (Native Americans, Latinos, Asian-Americans, and African-Americans), women who’ve had gestational diabetes or given birth to big babies (9 pounds or more), people with high blood pressure, people with high-density lipoprotein (HDL) levels at or below 35 mg/dl or triglyceride levels at or above 250 mg/dl, and individuals who have impaired fasting glucose or impaired glucose tolerance.

How is a fasting plasma glucose test done?

The fasting plasma glucose test is performed after a person has fasted for at least 8 hours. A sample of blood is taken from a vein in the arm. If the blood glucose level is greater than or equal to 126 mg/dl, the person is retested and, if the results are consistent, diagnosed with diabetes. (Until a few years ago, the diagnostic cut-off point was 140 mg/dl, but the ADA lowered it because research has shown that even people with fasting plasma glucose levels between 126 mg/dl and 140 mg/dl tend to develop the medical complications of diabetes.)

Individuals with a fasting plasma glucose level less than 126 mg/dl but greater than or equal to 100 mg/dl are classified as having impaired fasting glucose. Though they do not have diabetes, these individuals do not metabolize glucose normally, and they have an increased risk of developing high blood pressure, blood lipid disorders, and Type 2 diabetes.

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