Fasting and Non-Fasting Bloods

What is the difference between a fasting and non-fasting blood test?

A fasting test gives you a ‘bottom line’ result – this is the lowest you can expect the sugar and cholesterol figures to be.

If you have eaten just before the test, then the levels of sugar and cholesterol are determined by what you have just eaten – not by your body’s ability to handle these substances.

  • If a non-fasting level is high, it might not mean anything at all is wrong.
  • If a fasting level is high, then something is definitely wrong.

Why is fasting necessary and if you do eat what does it do to the results of the tests?

A fasting glucose test is conducted to determine the amount of sugar or glucose that is in your blood, after refraining from eating or drinking for a set time prior to the test.

This test is also known as a “blood sugar” or “plasma glucose” test.

This test is usually the first one conducted when diagnosing diabetes and may also be used periodically to monitor the progress of diabetic individuals.

 The test is simple, relatively painless and takes very little time to perform, although it does require advance preparation in order not to disrupt the results.


For a fasting “blood sugar” test, the doctor, nurse or health care assisstant will have asked you to not eat or drink anything except water for at least eight hours, prior to having your blood test.

 If you have any specific nutritional needs that may impact on your ability to fast for the required length of time, please notify the Practice as soon as possible.