It depends on the type of blood test you’re having.
If you have any questions about your blood test, ask your healthcare professional for advice.
Preparations for blood tests
You can eat and drink as normal before some blood tests. However, for others you may be given specific instructions so that the test results aren’t affected, for example, not to eat and sometimes not to drink before your test (known as a fasting blood test).
Below are some examples of different blood tests and what you may need to do to prepare for them, including how long you may need to fast. However, you should also follow any instructions from your healthcare professional.
Fasting blood glucose test
Do not eat or drink anything except water for 8-10 hours before a fasting blood glucose test. These are used to diagnose diabetes, a condition caused by too much glucose (sugar) in the blood.
Iron blood test
Iron blood tests are usually taken in the morning before you eat anything. You should also avoid taking iron pills or tablets for 24 hours before your test. Your body absorbs iron very quickly from food or pills, so this can raise your iron levels and affect the test results.
Iron blood tests help diagnose conditions such as iron deficiency anaemia (lack of red blood cells caused by low iron levels).
Blood cholesterol tests (lipid profile)
Do not eat anything and only drink water for 10-12 hours before having blood cholesterol tests (lipid profile).
Cholesterol is a fatty substance that can build up in your arteries and increase your risk of conditions such as heart disease.
There are several different cholesterol tests. When these are done together it’s called a lipid profile. A lipid profile tests the levels of:
- ‘good’ (HDL) cholesterol
- 'bad’ (LDL) cholesterol
- total cholesterol
- triglycerides (other fatty substances)
Some laboratories can calculate your LDL cholesterol level from your total cholesterol, triglycerides and HDL levels. However, you will still need to fast for these tests. If you do not need to fast, your healthcare professional will let you know.
If you’re just having a triglycerides test, do not drink alcohol for 24 hours before the test (you’ll also need to fast as explained above).
GGT (gamma-glutamyl transferase) test
A GGT test is used to help diagnose liver disease. Do not eat for at least eight hours before the test and do not drink alcohol for 24 hours before the test. Smoking can also affect the test results. Your healthcare professional will tell you if you need to stop smoking before the test and how long for.
PSA (prostate-specific antigen) test
A PSA test is used to detect prostate enlargement and prostate cancer. Avoid sexual activity and vigorous physical activity for two days before the test.
Last Updated: 28 November 2011