Healthdirect Free Australian health advice you can count on.

Medical problem? Call 1800 022 222. If you need urgent medical help, call triple zero immediately

healthdirect Australia is a free service where you can talk to a nurse or doctor who can help you know what to do.

beginning of content

Fasting for medical tests

You may be asked to fast by your doctor or nurse. For some medical tests, fasting beforehand gives a more accurate result. For other tests or operations, you need to fast for safety reasons. Your doctor can tell you what to do to prepare for your test.

What is fasting?

Fasting means not eating and only drinking sips of water. If you are fasting, you can't drink fruit juice, soft drink, coffee, tea or milk, and you can't eat or suck on lollies and chewing gum.

Fasting for tests

Fasting for blood tests

A fasting blood test is usually done in the morning after you have fasted for 8 to 16 hours.

Fasting for a gastroscopy

You need to fast for 6 hours before a gastroscopy. This is to lower the risk of vomiting up and inhaling what's in your stomach. It also gives the doctor a clear view inside the stomach and intestine.

Fasting for a colonoscopy

Before a colonoscopy, you eat a low-fibre diet for 2 to 3 days, and have only clear fluids the day before, such as black coffee, apple juice, water or clear jellies. If you have diabetes, make sure you get the right amount of glucose in these fluids. The day before, you also take a medicine to empty your bowel. Finally, for several hours before the procedure you need to fast.

Fasting before an anaesthetic

If you are being sedated or having a general anaesthetic, your doctor will ask you to stop eating several hours beforehand. You can have small amounts of clear fluids up to 2 hours before.

Special considerations for fasting

Medication

Keep taking your medication as usual before a test, unless your doctor instructs you otherwise. Some medications need to be stopped, so be sure to tell your doctor everything you are taking.

Diabetes

If you are diabetic and you need to fast:

  • check your blood sugar regularly (every 2 hours for example)
  • you may need to reduce your insulin dose or skip oral treatments
  • look out for signs of hypoglycaemia (a 'hypo')
  • if you are having a hypo, treat it - even if this means breaking your fast
  • avoid driving.

Contact your doctor if you have concerns about your blood sugar levels, staying well while fasting or if you have to break your fast.

Last reviewed: October 2015

Need more information?

These trusted information partners have more on this topic.

Found 1093 results

HDL cholesterol - Lab Tests Online AU

If this test is being performed as part of a complete lipid profile then fasting for about 12 hours is required, only water is permitted.

Read more on Lab Tests Online website

What do the numbers mean? - Diabetes NSW - Live your life

The diagnosis of diabetes or pre-diabetes, also known as Impaired Fasting Glucose (IFG) or Impaired Glucose Tolerance (IGT), must always be made on a laboratory blood glucose test. Find out what the blood glucose test numbers mean.

Read more on Diabetes NSW website

Pre-diabetes

There are 2 types of pre-diabetes: impaired glucose tolerance (IGT) and impaired fasting glucose (IFG).

Read more on WA Health website

Cardiomyopathy

Cardiomyopathy is a condition in which your heart muscle becomes inflamed and enlarged. Because it is enlarged, your heart muscle is stretched and becomes weak. This means it cant pump blood as fast as it should.

Read more on WA Health website

What to expect - ANZCA

Read more on ANZCA – Australian and New Zealand College of Anaesthetists website

Iron studies - Lab Tests Online AU

Your doctor may request that you fast for 12 hours prior to some iron tests; in this case, only water is permitted.

Read more on Lab Tests Online website

Understanding your tests - Lab Tests Online AU

This page aggregates information that directly links to Lab Tests Online.

Read more on Lab Tests Online website

Understanding your tests - Lab Tests Online AU

This page aggregates information that directly links to Lab Tests Online.

Read more on Lab Tests Online website

LDL cholesterol - Lab Tests Online AU

As part of a regular examination with a total cholesterol test or lipid profile or if your total cholesterol is high

Read more on Lab Tests Online website

Cholesterol tests - myDr.com.au

Abnormally high cholesterol levels may not give you any symptoms, so a blood test is the best way to check whether you have high cholesterol.

Read more on myDr website

Check your symptoms Find a health service

Healthdirect 24hr 7 days a week hotline

24 hour health advice and information you can count on

1800 022 222

Government Accredited with over 140 information partners

We are a government-funded service, providing quality, approved health information

Australian Government, health department logo ACT Government logo New South Wales government, health department logo Northen Territory Government logo Government of South Australia, health department logo Tasmanian government logo Government of Western Australia, health department logo
Feedback