Find out what to expect when you come to our clinics for your blood test.

Patient information

Before your appointment

Most patients are seen on a walk-in basis as requested by their GP or a clinical staff member. If you are coming at the request of your GP please bring your blood test referral form with you. Please note that the blood testing service at St Mary's Hospital does not accept referrals from GPs. All patients referred by their GP should contact their own GP practice to find the right place to have their blood test done. 

Some patients with diabetes and those who are having a fasting glucose and lipid (cholesterol) test need to fast from midnight on the morning of the test, if you are unsure please contact your GP.

You are welcome to bring a relative, close friend or carer with you to your appointment but please note we are limited with space in our clinic.

Please make sure you are wearing something with the ability to roll up your sleeve.

As of 1 April 2019, we will be extending the blood test opening hours at Hammersmith and Charing Cross Hospital. The new opening hours will be: 08.00 to 18.45, Monday through Friday.

During your appointment

Blood tests take place in our phlebotomy department, outpatient reception staff will be happy to direct you.

When you have your blood test there is a very low risk that bruising could occur in conditions which include:

  • drugs such as warfarin or aspirin
  • conditions such as a bleeding disorder or low platelets (thrombocytopenia)
  • when it is hard to get a vein, for example if the arm is swollen

What happens during a blood test?

A test usually involves placing a needle attached to a stylet into one of the blood vessels in the inside of your elbow or the back of your hand. You will feel a sharp scratch as the needle goes in but this isn't particularly painful.

Most blood tests only take a few minutes to complete.

After your appointment

If you were asked to fast before your test, it is possible you will feel light-headed afterwards, so please have a drink and something to eat afterwards.

The time scale for the results varies depending on the type of test. The requesting clinician for the blood test will be able to advise on approximate time scale for the test result.

Patient information leaflets