Blood tests

A blood test is where a sample (small amount) of your blood is taken with a needle.

Why do I need a blood test?

People have blood tests so that their blood can be checked. The blood is checked in place called a ‘laboratory’.

The most common blood tests check the cells in your blood. This includes the red blood cells, white blood cells and platelets (small, round cells that help your blood clot).

By checking the blood cells, doctors can see if you have an infection. They can also check for things like anaemia or leukaemia.

People also have blood tests to see if their medicine is working. If you have diabetes you will often have to have blood tests. This is to check the level of sugar in your blood.

What happens?

A doctor or nurse will use a needle to take a small amount of blood (sample). He or she will clean the area before putting the needle in. The needle will go in the inside of your elbow, your wrist or the back of your hand.

Sometimes people are given some cream to numb the area first, but it shouldn’t hurt much anyway.

Afterwards you will be asked to press on the area.

This is to stop you getting a bruise on your arm. He or she will then give you a plaster (or bandage if you are allergic) to put on your arm.

If you feel weak or dizzy during the blood test, tell the person taking the blood.

When can I go home?

You can usually go home straight after your blood tests.

When can I find out the results?

Your doctor may ask you to come to visit when the results are back. Sometimes you will be asked to phone the surgery.

Last reviewed by Great Ormond Street Hospital: 24 August 2006