How to prepare for a blood test
Published · 3 min read · General medicine
Preparation matters because the same person’s glucose and cholesterol can look quite different first thing in the morning and after lunch. Doctors read results against reference ranges, and those ranges are set for fasting blood.
When and how to come
- Come for your blood test in the morning, between 8 and 11.
- Leave 8–12 hours after your last meal: have dinner before 8 pm.
- Do drink water: when you are dehydrated a vein is harder to find.
- No tea, coffee, juice or chewing gum in the morning.
- The day before, avoid alcohol, heavy fatty food and hard exercise.
Medication
Don’t stop medicines you take regularly on your own. If your thyroid hormone (TSH) is being checked, take your morning dose after the test. Iron supplements are usually paused for 5 days before a ferritin test, but agree this with your doctor.
Children
Children find fasting hard: bring a baby 3–4 hours after a feed. Tell your child beforehand what is going to happen. Our blood-test room has a separate chair for children, and taking the sample usually takes less than a minute.
Most results arrive the next working day through a link in a text message. If you see a number outside the range, don’t worry yet: your doctor will look at it together with your symptoms.
This article is for information and does not replace a visit to a doctor.
