The First Steps With Having a Blood Test
Having a Blood Test: the few things that matter most, and the mistakes that catch people out early.
A sample taken from a vein, usually in the arm, for one of several hundred different tests.
Key takeaways
- How long it takes: usually under five minutes
- Fasting: needed only for some tests; follow the instruction you were given
- Most useful single change: Drink water beforehand unless told otherwise, which makes veins easier to find.
- Commonest mistake: Fasting for a test that does not need it, particularly if you have diabetes.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
Why bother
Most of the preparation that matters is decided by which test it is, so the instructions you are given override any general advice.
Start here
Two things, and nothing else until both feel routine.
- Drink water beforehand unless told otherwise, which makes veins easier to find
- Say if you have fainted at a blood test before, so you can lie down
Then add these
When those have settled in, these are worth adding.
- Keep pressure on the site for a couple of minutes afterwards
- Ask how you will be told the result, and what happens if it is normal
The numbers, in one place
| Measure | Figure |
|---|---|
| How long it takes | usually under five minutes |
| Fasting | needed only for some tests; follow the instruction you were given |
| Results | commonly a few days, longer for specialist tests |
| Afterwards | bruising is common and settles within a week |
Common early mistakes
- Fasting for a test that does not need it, particularly if you have diabetes
- Assuming no news means a normal result without checking
- Heavy lifting with that arm straight afterwards, which encourages bruising
Where to go next
- Having a Blood Test: Common Myths and What Guidelines Say
- A Q and A on Having a Blood Test
- Having a Blood Test — the reference entry
- The Evidence on NHS Referrals and Waiting Times, Without the Hype
- The Evidence on Asking for a Second Opinion, Without the Hype
When to speak to a doctor
See a doctor if the puncture site becomes hot, swollen, increasingly painful or oozes over the following days. Tell your GP before the test if you take anticoagulants or have a bleeding disorder.
Where this comes from
- NHS — Blood tests
- Lab Tests Online UK — Understanding your tests
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.
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