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Full blood count

A full blood count, or FBC, is a very common blood test. Doctors use this to check a person's general health as well as screening for specific conditions, such as anaemia.

The number of red cells, white cells and platelets in the blood are checked. Red cells carry oxygen around the body and haemoglobin makes up part of the red cells. White cells are used by the body to fight infections. Platelets are important for clotting blood and stopping bleeding.

How is the full blood count carried out?

A small sample of blood is taken from a vein in the arm by a nurse, doctor or phlebotomist: someone specially trained to collect blood from patients for laboratory tests. The test may be taken in a clinic, GP's surgery or hospital department.

The area of skin where the needle will go in to take the sample may be cleaned with an antiseptic wipe. A tourniquet is then usually put round the upper arm to make the vein swell to make it easier to take the sample.

A slight pricking sensation may be felt from the needle. If a person is nervous about needles, the person taking the sample should be told so they can make the patient feel more at ease.

One collection needle device can be used to collect several samples for different types of blood test.

After the test, pressure is put on the small puncture in the skin for several minutes with a cotton wool pad. This stops any bleeding and helps prevent bruising. A plaster is usually applied to keep the area clean and prevent infection.

The vial of blood is sent to a laboratory where the different types of blood cells are measured or counted.

Full blood count results

The results of the full blood count test will be known quickly, or in a few days, depending on the urgency of the test.

Results may be given to doctors in hospital for day case patients or people admitted to wards, or may be sent to the GP who arranged the test. The doctor will need to study and interpret the results before explaining them to a patient and arranging any further investigations.

The results don't always give a definitive diagnosis, but can give pointers about health problems, which may then require further investigation.

Low haemoglobin suggests a person has anaemia. The reasons for this would then need to be investigated, such as a poor diet or conditions causing internal bleeding.

High haemoglobin could indicate lung disease or bone marrow problems.

Low white blood cell count. Bone marrow problems, including bone marrow cancer, may be indicated if the test shows a low white blood cell count. It could also be due to a viral infection or be down to a person’s genetic make-up and of no clinical significance. It is also important to monitor the white cell count during chemotherapy treatment for cancer.

High white blood cell counts may suggest the body is fighting off an infection, or in rare cases, it might be a sign of leukaemia or blood cancer.

Low platelet counts could also signify a viral infection. It could also be due to an autoimmune condition in which the body's immune system turns on itself attacking healthy tissue.

High platelet counts can mean inflammatory conditions, an infection, or bone marrow conditions.

WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on October 31, 2012

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