Fasting Blood Sugar Test

What Is a Fasting Blood Sugar Test?

A fasting blood sugar test (also called a fasting plasma glucose or FPG test) measures the amount of glucose (sugar) in your blood after you’ve fasted (had nothing to eat or drink except water) for at least 8 hours. This test is a simple and reliable way to screen for diabetes or prediabetes.

It is one of the most commonly used blood tests to assess how well your body regulates blood sugar levels and is often the first step in diagnosing diabetes.

Why Is the Test Done?

Your healthcare provider may recommend a fasting blood sugar test if:

• You’re showing symptoms of high blood sugar (such as fatigue, frequent urination, or extreme thirst)
• You have risk factors for diabetes or prediabetes, including being overweight, inactive, or having a family history of diabetes
• You’re being monitored for existing diabetes
• You’re pregnant and being screened for gestational diabetes
  
  

Fasting glucose test results help:

• Diagnose prediabetes or diabetes
• Guide treatment decisions
• Track how well diabetes is being managed

How to Prepare for the Test

• Do not eat or drink anything (except water) for 8–12 hours before your blood test.
• Take any medications as directed unless your doctor advises otherwise.
• You may be asked to schedule the test early in the morning to make fasting easier.
  
  

What Happens During the Test

1. A healthcare professional will draw a small sample of blood, usually from a vein in your arm.
2. The procedure typically takes just a few minutes.
3. After the sample is taken, you can eat and return to normal activities.
   
   

Understanding Your Results

• Normal: Less than 100 mg/dL
• Prediabetes: 100–125 mg/dL
• Diabetes: 126 mg/dL or higher on two separate tests
  
  

Your provider will review your results and may recommend further testing, such as an A1C or glucose tolerance test.

This test is very safe and routine. Minor risks may include:

• Slight pain or bruising at the blood draw site
• Lightheadedness (rare)
  
  

There are no serious side effects, and you can resume your daily routine right away.