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Why you have blood tests

Blood tests can

  • Check your general health, including how well your liver, kidneys, heart and other organs are working
  • Check the numbers of different types of blood cells
  • Help to diagnose cancer and other conditions
  • Check for infections
  • Help to find out if a cancer has come back

How you have the test

A doctor, nurse or phlebotomist may do the test. They can take the blood from any vein but usually use a vein in the inner part of your elbow. They put a small needle into your vein and attach a syringe or small bottle to draw out some blood. Then they take the needle out and put a cotton wool ball or small piece of gauze on the area.

Before the blood test

You can eat and drink normally before most blood tests. But for some tests you need to stop eating and drinking some time beforehand. Your doctor or nurse will tell you if you need to do this and for how long. You may also need to stop taking certain tablets for some tests, so check with your doctor or nurse.

Getting the results

You may get the results of some tests within a couple of hours – for example, a full blood count. Other types of test may take a few days or a few weeks.

 

CR PDF Icon You can view and print the quick guide for this page about blood tests.

 

 

Why you have blood tests

Blood tests can

  • Check your general health, including how well your liver, kidneys, heart and other organs are working
  • Check numbers of blood cells
  • Help diagnose cancer and other conditions
  • Check for infections
  • Help to find out if a cancer has come back

Tests that you might have include

The links above take you to descriptions of these tests.

 

Before your blood test

You can eat and drink normally before most blood tests. But for some tests you need to stop eating and drinking for a while beforehand. This is called fasting. Tests that you might need to fast for include

  • Glucose tests
  • Cholesterol tests

Your doctor will tell you how long you need to fast for.

For tests that check the levels of particular substances in the blood you may need to stop taking certain tablets, such as iron or thyroxine. Check with your doctor beforehand whether you need to stop taking tablets.

 

Having a blood test

You sit or lie down to have the test. Your doctor, nurse, or someone who specialises in taking blood (a phlebotomist) takes the sample. They can take it from any vein but usually use one in the inner part of your elbow. First you have a tight band put around your upper arm. Then you have a small needle put into your vein. The person taking the blood attaches a syringe or small bottle to the needle and draws out some blood. They then release the band around your arm, take the needle out and put a cotton wool ball or small piece of gauze on the area.

You need to press down on the cotton wool or gauze for a few minutes to help stop bleeding and bruising. You may then have a plaster put over the area to keep it clean. The blood sample goes to the laboratory for testing.

Many people don’t like needles and don’t like the sight of blood. Some feel faint at the sight of it. Tell the person taking the blood if you are worried or you start to feel faint. You may want to look away while they take the blood.

After the test you may have a small bruise where the blood was taken from. But most people can only see a very small mark.

 

Getting your results

Ask your doctor when you are likely to get the results and who will give them to you. You can get the results of some tests within a couple of hours - for example, a full blood count. Others take a few days.

Some tumour marker tests take a few weeks. Genetic tests can take from a couple of weeks to a few months.

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Updated: 14 August 2013