A blood test is when a sample of blood is taken for testing in a laboratory. Blood tests have a wide range of uses and are one of the most common types of medical test. For example, a blood test can be used to:
- assess your general state of health
- confirm the presence of a bacterial or viral infection
- see how well certain organs, such as the liver and kidneys, are functioning
A blood test usually involves the phlebotomist taking a blood sample from a blood vessel in your arm. The usual place for a sample is the inside of the elbow or the back of the hand where the veins are relatively close to the surface. Blood samples from children are most commonly taken from the back of the hand. The child's hand will be anaesthetised (numbed) with a special cream before the sample is taken.
If you are due to have a blood test please refrain from eating meat or fish for 12 hours prior to the test. If you forget, don't worry, but this could affect the results and you may asked to return for a repeat test.
You can find out more about blood tests, their purpose and the way they are performed on the NHS Choices website.