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 is the inside of the elbow or wrist, where the veins are relatively close to the surface.
Blood samples from children are most commonly taken from the back of the hand. Children aged 10 years and under will need to attend Queen Mary's Hospital for Children (at the back of St Helier Hospital). The GP will give you a form to take and you will need to ring 020 8296 2846 to arrange an appointment. The child's hand will be anaesthetised (numbed) with a special cream before the sample is taken.
Please note that for a fasting blood test you should eat nothing for 12 hours beforehand and drink plenty of plain water only.
You can find out more about blood tests, their purpose and the way they are performed on the NHS Choices website.