Fasting before blood tests

In the hours after you eat, many chemicals in your blood undergo significant changes. Further changes can occur if you do not eat for an extended period (more than 16 hours). Because of this, many blood tests should be collected in the morning after an overnight fast.

Fasting means that you eat and drink nothing except water for 8 –16 hours before your blood test (12 hours optimal).

General guidelines:

  • During your fast, you may drink water, but it must contain no additives (e.g. tea, coffee, or cordials). You should avoid alcohol for 24 hours (1 day) prior to the test, if possible.
  • Unless your doctor advises otherwise, you should continue taking any current medications. 
  • Smoking cigarettes should be avoided while fasting.
  • You should try to avoid fasting for more than 16 hours.
  • Diabetics should not fast without medical advice.
  • Children under 12 should avoid fasting for more than 4-6 hours.

Your doctor will advise if you are required to fast for your blood test.

For more information, please telephone Patient Services Support on 1300 732 030.

Item number 34167 - Issue date November 2019