Fasting before a blood test is a common requirement to ensure accurate results. By abstaining from food and drink for a specified period, patients can help their healthcare providers obtain a clear picture of their health. This simple yet crucial step aids in the diagnosis and management of various medical conditions, making it an essential part of the blood testing process.

How Long Should You Fast Before a Blood Test?

For a fasting blood test, you typically need to fast for 8 to 12 hours before your appointment. This means no eating or drinking anything other than water. It’s crucial for getting accurate results, especially for lipid profile, glucose, and cholesterol tests.

However, this will depend on the type of blood work you’re having. Some tests don’t require a fasting period or any type of preparation beforehand. Our AHPRA-accredited doctors will advise you during your video consultation if any fasting is necessary and how long you should fast before providing a blood test referral.

You can also ask the staff at the pathology collection centre if you’re not sure you’ve fasted long enough. If fasting is necessary for your blood test, they’ll also ask you about it before blood collection is done.

Remember, sticking to your fasting period ensures your test results reflect your true health status. If you have any questions, it’s best to reach out to your healthcare provider for advice tailored to your needs.

man on his phone with the online doctor

Do I Have to Fast Before A Blood Test?

Fasting before a blood test is crucial for several reasons:

  • Stabilises Blood Components: Fasting helps stabilise levels of enzymes and proteins that could be altered by food intake.
  • Reduces Variability: Eating can introduce variability in blood components like triglycerides and HDL (high-density lipoprotein), making it harder to interpret test results.
  • Improves Diagnostic Accuracy: Accurate results give healthcare professionals a clear picture of your health status. This, in turn, leads to more accurate medical advice and treatment plans.
  • Safety Reasons: Tests like endoscopy and biopsies of internal organs are typically done under general anaesthesia. Fasting lowers your risk of serious complications.

Types of Blood Tests That Require Fasting

Getting some blood work done doesn’t always mean you’ll have to fast. Here are some of the most common types of blood tests that require fasting:

  • Blood Glucose Test: This test checks how well your body manages blood sugar, which is crucial for diagnosing and managing diabetes. You’ll need to fast for at least 8 hours.
  • Lipid Panel: Set aside 9 to 12 hours for fasting before this test. This is necessary to accurately measure your cholesterol levels, including HDL and LDL.
  • Liver Function Tests: These require a fasting period of 10 to 12 hours. They help check the health of your liver by looking at enzymes and proteins that liver cells release.
  • Kidney Function Panel: Plan to fast for 8 to 12 hours. This panel gives insights into how well your kidneys are filtering waste and maintaining electrolyte balance.
  • Iron Tests: A 12-hour fast is needed here. It measures how much iron is in your blood, helping to diagnose conditions like anaemia or iron overload.

Pathology tests like complete blood count (CBC), thyroid function, PSA, and STI tests don’t require you to skip meals. However, if you’re not sure, it’s always a good idea to confirm with your healthcare provider or the pathology collection centre whether fasting is necessary for your specific test, as guidelines can vary.

Chat With an Online Doctor Now

Instant access to chat with a doctor with a comprehensive range of services

With Instant Consult, you can chat with a doctor and get help for a wide range of medical requests, all from the comfort of your home!


Medical Certificates

Are you too ill to come into work and need to give your boss a medical certificate? With Instant Consult you can chat with a doctor and get a medical certificate sent directly to your app’s inbox, all without getting out of bed!



If you need a new prescription or need to update an ongoing one then you can use our app to instantly chat to a doctor who can prepare your prescription promptly!



If you have a medical condition that needs treatment from a specialist, one of our GP’s can send a digital referral straight to your app’s inbox.


Pathology Requests

If you need a blood cell count or to check for STDs/STIs or need any other kind of bloodwork you can easily get a pathology request sent to your inbox by any of our fully licensed online GPs. You can then take the request to the clinic of your choice.


Radiology Requests

If you require any special kind of diagnostic imaging such as a CAT scan or an MRI you can get a request from one of our online GPs which you can then take to your preferred provider.

What Can I Eat or Drink While Fasting?

When fasting for a blood test, the goal is to avoid any foods or drinks that could skew your test results. That means your food and drink options are limited.

You cannot eat any solid or liquid food, especially those that can affect your blood glucose levels. This includes meals, snacks, and any type of food that needs to be chewed or swallowed.

As for beverages, avoid all drinks except water. That means no coffee, tea, soda, juice, and especially alcohol. Even smoking and chewing gum is not allowed. Nicotine in cigarettes can affect some test results, while most gums contain sugars or artificial sweeteners. So, it’s best to avoid them altogether.

In short, the only thing you can have during your fasting period is water. In fact, drinking water is encouraged as it helps keep you hydrated and can make it easier to draw your blood. If you feel hungry, just drink plenty of water and make sure to get enough sleep, as lack of sleep can increase hunger and appetite.

Taking Medications While Fasting

Generally, you can take your usual medications while fasting unless your doctor tells you otherwise. But make sure to only take it with water. For medications that need to be taken with food, it’s a good idea to check with your doctor first. Make sure to tell your doctor about any medications you’re taking, including over-the-counter ones.

Fasting Precautions for Diabetics

Fasting for a blood test when you have diabetes needs a bit of extra care. Here are some precautions you should take:

  • Talk to Your Doctor: Before fasting, it’s crucial to discuss it with your healthcare provider. They can adjust your medication or insulin to match the fasting requirements.
  • Monitor Your Blood Sugar: Keep a close eye on your levels before, during, and after the fast. This helps prevent any lows or highs.
  • Stay Hydrated: Drinking water is okay and encouraged. It won’t affect your blood sugar levels and keeps you hydrated.
  • Have a Plan for Lows: If your blood sugar drops, treat it as you normally would, even if it means breaking the fast. Your safety comes first.
  • Post-Test Meal: Plan a healthy meal for after your test. This helps stabilize your blood sugar levels once you can eat again.
Chat With an Online Doctor Now

What If I Accidentally Eat or Drink Something I Shouldn't?

If you accidentally eat or drink something you shouldn’t while fasting for a blood test, don’t stress too much. Just make sure to let the staff at the collection centre or your healthcare provider know as soon as you arrive. They’ll help you figure out the next steps.

Sometimes, depending on what you had and the type of test you’re doing, they might go ahead with the test. Other times, they might reschedule it for another day to ensure your results are accurate.

Remember, it’s important to be honest about what happened. This ensures your healthcare team has all the information they need to take care of you properly.

Mistakes happen, and they’re used to dealing with situations like this. Your health and getting reliable test results are what matter most.

fasting for blood test

When Can I Drink or Eat Again?

Once you’ve had your blood test, you can eat and drink right away. There’s no need to wait. It’s a good idea to bring a small snack or drink with you to the collection centre, especially if you’ve been fasting for a while. This helps you feel better quickly and stabilises your blood sugar levels if they’ve dropped.

If you’re diabetic or have any other health conditions like high blood pressure that require careful monitoring of your food and drink intake, just make sure to choose something that fits within your usual dietary guidelines.

Need a blood test referral? Instant Consult is here to help. Simply book a consultation to chat with our doctors and get your referral in no time – all without leaving your home!

But that’s not all. We also offer online prescriptions, medical certificates, specialist referrals, and radiology requests. It’s all the healthcare services you need without stepping out your door. Book a consultation today and take the first step towards managing your health with ease.

community of doctors icon

Community of Doctors

Australian registered, fully qualified, insured and experienced Doctors right at your fingertips ready for an instant online consult