Blood tests

What are blood tests?

Blood tests can check your general health, or look for certain changes in your blood.

Why do I need to have blood tests?

Blood tests are done for different reasons:

  • To measure the number of red blood cells, white blood cells and platelets in your blood. This is called a full blood count (FBC).
  • To check how well your liver, kidneys and hormones are working.
  • Some cancers make chemicals called tumour markers. Blood tests can check for these markers. This helps to diagnose some cancers and check how well treatment is working.
  • To check for an infection in your blood.

If you are having chemotherapy, you will have blood tests before each treatment. This is to make sure your blood cells are at the right level for you to have your treatment.

What happens?

Blood samples are usually taken from a vein in your arm, unless you already have a line (PICC, Hickman®, or portacath).

You will be sitting down when you have a blood test. Seeing blood or needles can make some people feel dizzy or faint. Let the person taking your blood (phlebotomist) know if you feel like this.

The phlebotomist puts a tight band around your arm. They clean the skin and gently insert a small needle. It can feel like a scratch or a slight sting when it goes in, but it should not be painful. If you are worried about it hurting, you can ask to have an anaesthetic cream or a cold spray to numb the area. The blood is withdrawn into small tubes.

After the test

Afterwards, they will put a cotton pad or a plaster over the area. Your doctor or nurse will explain your results when they are ready.