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Fasting Blood Sugar Test

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What is a Fasting Blood Sugar Test?

A fasting blood sugar test is a diagnostic test that measures glucose levels in the blood after an overnight fast. Normally glucagon is produced in the body when blood sugar is low that prompts conversion and release of stored glucose from the liver into the blood. Once the glucose levels cross required levels insulin is produced by the pancreas that helps the body to consume glucose. For those with diabetes, this fine balance is disrupted causing high levels of sugar in the bloodstream.

Why is it conducted?

This test is used both for screening and monitoring purposes. Diabetes has a wide ranging impact on the body and timely detection can help to keep it under control.

Who should go for it?

Persons who have risk factors are often advised this test for screening purposes.

  • Among the risk factors are obesity or at least one parent has diabetes.
  • People who are above the age of 45 are also advised this test for screening purposes.
  • Those who have already been diagnosed with diabetes are advised fasting blood sugar test to monitor the response to treatment.


This is a simple blood test that is done in the morning before eating or drinking anything as this can affect results. You can have water if you wish.

Interpretation of results

The normal ranges for fasting blood sugar are 100 mg/dL (5.6 mmol/L). If the results are between   100 to 125 mg/dL (5.6 to 6.9 mmol/L), it indicates prediabetes. If the results are higher than this, it indicates diabetes.

Written by: Nandita tripati

Date last updated: January 10, 2015