Blood tests - How a blood test is performed
NHS Choices Medical Reference
A blood test usually involves taking a blood sample from a blood vessel in your arm.
The arm is a convenient part of the body to use because it can be easily uncovered. The usual place for a sample to be taken from is the inside of the elbow or wrist, where the veins are relatively close to the surface.
Blood samples from children are usually taken from the back of the hand. The child's hand will be anaesthetised (numbed) with a special cream before the sample is taken.
A tight band (tourniquet) is usually put around your upper arm. This squeezes the arm, temporarily slowing down the flow of blood out of the arm, and causing the vein to swell with blood. This makes it easier for a blood sample to be taken.
Before taking the sample, the doctor or nurse may need to clean the area with an antiseptic wipe.
A needle attached to a syringe or to a special blood collecting container is pushed into the vein. The syringe is used to draw out a sample of your blood. You may feel a slight pricking sensation as the needle goes in, but it should not be painful. If you do not like needles and injections, tell the person who is taking the sample so they can make you more comfortable. If you feel faint, lie down.
When the sample has been taken, the needle will be removed. Pressure is applied to the tiny break in the skin for a few minutes using a cotton-wool pad to stop the bleeding and to prevent bruising. A plaster may then be put on the small wound to keep it clean and prevent infection.
After the test
After the blood sample has been taken, it will be put into a bottle and labelled with your name. It will then be sent to a laboratory where it will be examined under a microscope or tested with chemicals, depending on what's being checked. The results are sent back to the hospital or to your GP, and you will be told when and how you will be given them.
Sometimes, receiving results can be stressful and upsetting. If you are worried about the outcome of a test, you may choose to take a trusted friend or relative with you. For some tests, such as HIV, you will be offered specialist counselling to help you deal with your results.