Blood tests

Blood tests involve taking samples of your blood which are then looked at in a laboratory. You usually have these in the outpatient clinic or in King's Phlebotomy Department.

What are they used for?

Test tubes in a rack

They can be used to:

  • check your general health, including how well your organs (such as your liver, kidneys and heart) are working
  • check numbers of blood cells
  • help diagnose cancer
  • help diagnose other conditions
  • check for infections
  • find out if a cancer has come back.

Do I need to prepare?

You do not need to prepare for most blood tests. But for some you need to stop eating and drinking for a while beforehand. We will tell you if you need to do this and for how long.

We may also ask you to stop taking certain tablets for some tests.

What happens during the procedure?

Most blood tests only take a few minutes to complete. You usually have a needle attached to a syringe put into one of the blood vessels in the inside of your elbow or wrist. As the needle goes in you will feel a sharp prick. Samples of your blood are then taken and the needle is taken out.

You will be given a cotton-wool pad to put pressure on the site of the injection. This stops any bleeding and should help to prevent bruising.

There are lots of different tests, including

  • full blood count (FBC)
  • urea and electrolytes (U + Es)
  • liver function tests (LFT)
  • blood cultures
  • tumour marker.

NHS Choices has more information about blood tests.