Medical Questions » Pathology Questions » Question No. 781
| Question: | My doctor has ordered an FBC on the pathology form, and the receptionist said this was a full blood count, but couldn' t tell me why it was being done or what it involves. Can you help me? |
| Answer: | A full blood count (FBC) is the most frequently performed of all blood tests. It gives an enormous amount of information about your blood and the state of your overall health. A blood sample is taken from the vein on the inside of your elbow and smeared onto a glass slide.
The smear of blood is examined under a microscope and the number of different types of cells present are counted. Computers have now been programmed to do these counts very rapidly and automatically.
Blood cells consist of three different types—red cells (erythrocytes), white cells (leucocytes) and platelets (thrombocytes). Red cells carry the red pigment haemoglobin which is used to transport oxygen. There are several different types of white cells that fight infection, and platelets are one of the main factors that enable blood to clot.
A blood count determines the number of all these cells, their size, and the proportions in which they exist, as well as the amount of haemoglobin present. If you consult a doctor because you are unduly tired and lacking in energy, it may mean that you are anaemic, that you have an infection or some other disease, or simply that you are working too hard. By ordering a blood count, the doctor can often find out which it is.
If you are anaemic, you will have insufficient haemoglobin or too few red blood cells. If you have a bacterial infection it is likely that your white blood cells will have increased (leucocytosis) to fight it, while a viral infection often decreases white blood cell levels (leucopenia) as the virus destroys them. A lack of platelets (thrombocytopenia) will cause excessive bruising and bleeding as the blood is unable to clot normally.
If the full blood count is normal, further tests may be necessary to determine the cause of your tiredness, or reassurance may be all that is required.
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