How to prepare for a blood test: food, water and medicines
For many blood tests you need to fast, usually for 8 to 12 hours, and plain water is usually allowed. Your doctor or the laboratory gives the exact instructions for your tests; these are the general rules.
In short
- Fasting: usually 8 to 12 hours without food, unless your doctor or the lab says otherwise.
- Plain water is usually allowed; coffee, tea, juice and chewing gum are not.
- Do not skip medication on your own: ask your doctor whether to take it before or after the blood draw.
- Have the referral or the list of tests ready.
When you need to fast
Fasting means no food, usually for 8 to 12 hours before the blood draw. It is needed for tests that food affects, such as blood sugar and blood fats (cholesterol and triglycerides).
Some tests do not need fasting. If you are not sure, ask the doctor who gave the referral or the laboratory.
What you can and cannot have before the test
Plain water: usually yes, and it helps, because the vein is easier to find.
Coffee, tea, juice and milk: no, because they can change the result.
Chewing gum and sweets: no.
Alcohol: avoid it the day before the test.
Cigarettes: do not smoke on the morning of the test.
Hard physical exercise: avoid it the day before the test.
Medicines
Do not stop or skip your treatment on your own. Ask your doctor whether to take your morning medicines before or after the blood draw.
If you take blood thinners, tell the nurse before the blood draw.
How a blood draw at home works
We agree on a time, usually in the morning.
We check the referral or the list of tests.
We take the sample from a vein and label the tubes.
We take the sample to the laboratory we agree on, and the laboratory issues the results.
After the blood draw
Press the cotton pad on the puncture site for a few minutes.
After that you can eat and take your morning medicines, unless your doctor told you otherwise.
A small bruise at the puncture site is common and usually goes away on its own.
If the arm swells a lot, hurts or turns red, contact your doctor.
This is general guidance and does not replace medical advice. For your patient, your doctor's instructions come first.
Frequently asked questions
Can I drink water before a blood test?
Usually yes. Plain water without sugar is allowed even before fasting tests, unless your doctor or the laboratory tells you otherwise.
How many hours before a blood test should I not eat?
For fasting tests, usually 8 to 12 hours. Your doctor or the laboratory will tell you the exact time for your tests.
Can I drink coffee before a blood test?
Not before fasting tests. Coffee, even without sugar, can change some results. Have it after the blood draw.
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