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Before your blood test

Before having a blood test at St Mary’s Hospital

If you're coming for a blood test at St Mary’s Hospital, there are some things you should tell us.

For example, if you:

  • have had any problems with blood tests in the past, such as feeling faint
  • take medication that thins your blood, such as warfarin or aspirin.

The blood clinic is at its busiest between 9am and 1pm. If you are having routine blood tests, please try to avoid these times.

We must have the request form in order to perform a blood test. Please check the forms to ensure that your details are correct.

If you miss your turn while waiting for your blood test, you will need to take another ticket and wait for your turn again.

Taking your blood sample

When you enter the blood room, a member of staff will check your forms. One blood test request may require several different small bottles of blood, but these can be taken from a single skin puncture.

After we take your blood sample, we cover the puncture with a dressing. Apply pressure to this for at least three minutes to reduce the risk of bruising, and keep the dressing on for one hour. Avoid heavy lifting with that arm for several hours.

Fasting blood tests, glucose tolerance tests and other special blood tests

If you are having a fasting blood test, the doctor will ask you not to eat or drink on the day or your blood test.

For a glucose tolerance test, you should not eat or drink anything except plain water for at least 12 hours before the test.

Please arrive at the blood testing clinic before 9.30am because this blood test takes two hours to perform. We will take a blood sample when you arrive and then ask you to drink a glucose drink, such as Lucozade. After the drink you need to wait for 2 hours, then we will take a second blood test. During this time you must not eat, drink or take any vigorous exercise.

After the blood sample has been taken, you may eat and drink as normal.

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