Tests and procedures: Blood tests
Blood tests show the different types of blood cells in a child’s blood and any abnormal cells such as leukaemic cells.
They also show the functions of the body’s organs such as the kidneys, liver, lungs and muscle.
A blood sample can be taken a number of different ways:
- Finger prick blood test - it may be enough to make a small prick in the finger. This might be used for a full blood count, or for kidney or liver function tests.
- Venipuncture – if more blood is needed, or if it is thought that a finger-prick could interfere with the test, blood can be taken from a vein. A venipuncture might be used for blood cultures or blood clotting tests (more information below)
- Central venous device - if the child has a central line, or port-a-cath in place, the blood can be taken through this. However, each time this device is used, there is a risk of infection, therefore a central .line or port-a-cath will usually only be used for a blood test if it is being accessed for other reasons as well.
Blood cultures
A blood culture is a test to find and identify any bacteria or fungi that have infected the blood stream.
A child who develops a fever may have a blood culture done to find out what type of infection is causing the fever and which antibiotics to prescribe for the infection.
Blood count
This test, also known as a full blood count, measures the health of the bone marrow. A full blood count (FBC) is performed almost every time a child attends the hospital for treatment or follow-up.
A FBC is used to measure the hemoglobin (Hb), white blood cell (WBC) count, differential white cell count (including neutrophil count) and platelet (Plt) count.
Blood clotting and coagulation tests
When blood vessels are torn or damaged, a blood clot forms to stop too much blood from being lost
First, the platelets in the blood stick together to form a plug. Then the platelet plug is stabilised by fibrin strands. To form the fibrin strands, about 12 natural proteins called clotting factors are needed.
If a child does not have enough platelets, or a lack of clotting factors, blood clots will not form properly. Coagulation tests are done to look for any deficiency of clotting factors. Examples of coagulation tests include INR, APTT and PT.