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What are blood tests used for?

Blood tests can be as simple as a tiny prick on the finger to test diabetes blood sugar levels at home, to special containers being filled from a needle in the arm to be sent for laboratory testing.

Blood tests can help assess a person's general health, check for infections, monitor health conditions and treatments, check how specific organs are working and to screen for some genetic conditions.

How blood tests are carried out

Blood tests may be carried out in a GP's surgery, often by a nurse, in hospital or at a clinic by a specially trained phlebotomist - a person who takes blood samples.

For blood tests, you may be asked to make a fist a few times. Then a strap, called a tourniquet, is put around the arm before the skin is cleaned with an antiseptic wipe and a special needle is inserted through the skin and into a vein.

This doesn’t usually hurt much, and is a pin prick sensation. However, some people are nervous around needles and blood and may need reassurance.

Special containers are connected to the needle, filled and labelled. Several containers can be filled during the appointment, depending on what tests have been arranged.

After the needle is removed, a gauze pad needs to be held over the area until bleeding has stopped and a plaster is applied. Sometimes having a blood test can leave a small bruise for a period of time.

Having a blood test should usually take just a few minutes.

Even if several samples are taken, very little of the body's overall blood stores are used, so it shouldn’t make people feel dizzy.

Special instructions may be given before arranging a blood test, such as an early appointment for a fasting test to avoid being hungry for too long.

If a GP has sent you for a blood test, to a clinic or hospital, and you were given a form, make sure you take it with you so the phlebotomist knows what samples to take, and who to give the results to.

Blood test results are usually available from your doctor in a couple of days. In some cases they may contact you first, and people may be advised to have a friend or relative with them when they get their results if they find it stressful or upsetting.

Test results are usually based on a reference range, such as a reading a healthy person might have compared with someone with a health condition.

A-Z of common blood tests

Here are some common blood tests in our A-Z guide:

Amylase test and lipase test, to check the pancreas.

Blood cholesterol test, to check lipid levels to help assess heart disease risk.

Blood culture, where samples are taken from different parts of the body and tested to see if bacteria grow in culture dishes.

WebMD Medical Reference

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