Introduction
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
- screen for certain genetic conditions such as cystic fibrosis.
What happens during a blood test?
Most blood tests are carried out at your GP surgery or your local hospital under the supervision of a nurse, or in some cases, a doctor.
A test usually involves placing a needle attached to a syringe into one of the blood vessels in the inside of your elbow or wrist. You will feel a sharp prick as the needle goes it but this is not particualry painful.
A sample of blood is then taken and the needle is removed. You will be given a cotton wool pad to put on the the site of the injection which stops any bleeding and should prevent bruising.
Most blood tests only take a few minutes to complete.
Read more about how a blood test is performed.
Recovery
Only a small amount of blood is taken during the test so you should feel no significant after-effects.
However, some people do feel dizzy and faint during and after the test. If this does happen to you then tell the person carrying out the test so they can help you feel more comfortable.
After a blood test, you may have a small bruised area on your skin where the needle went in. Occasionally, a larger area of bruising may appear. This can be because there was a lack of pressure at the site of the jab or the blood vessel was damaged by the needle.
Bruises can be painful but are usually harmless. However, tell your GP if you frequently get bruises after having a blood test.
Blood
Blood is pumped around the body by the heart. It supplies oxygen to the body s organs, muscles and tissues, and removes carbon dioxide.
Blood is made up of:
- plasma - which is a mix of water and chemicals such a proteins, glucose and salt
- red blood cells - these carry oxygen from the lungs and transport it around the body
- white blood cells - these form part of the body s immune system and help defend the body against infection
- platelets - these are cells that help the blood to clot (thicken) when you cut yourself
Glossary
Blood test
During a blood test, a sample of blood is taken from a vein using a needle so that it can be examined in a laboratory.
Blood
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Oxygen
Oxygen is an odourless, colourless gas that makes up about 20% of the air we breathe.
Lungs
Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.
Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
Plasma
Plasma is the liquid part of blood, which holds other blood cells together.
Glucose
Glucose (or dextrose) is a type of sugar that is used by the body to produce energy.
