An FBC (Full Blood Count) is exactly what it says. The test counts the number of cells in your blood. The test usually uses a small pinkish red tube. So it counts the red cells, the white cells and the platelet cells.

Red, white and platelet cells

• Red blood cells

  The red cells are made of Haemoglobin and carry the oxygen and carbon dioxide around the body. When they leave the lungs the red cells are loaded with oxygen, they travel to the muscles and organs and there they deliver the oxygen. Then they pick up carbon dioxide and carry it to the lungs where they swap the carbon dioxide for more oxygen.

  The blood test counts how many red blood cells you have got in 100ml. So the result is so many grams per 100ml. Sometimes this expressed as a percentage, and a good count is 100%, or the actual figure of 15grams/per 100ml (which is 100%!). So you may hear "She's got a blood count of 7 or less than 50%".

  If you have a low red cell count, you are known as ANAEMIC. Most people have a blood count of about 12-14.5 grams/100ml, 84-95%. The commonest form of anaemia is when someone is short of iron, an essential element in making haemoglobin.

• White blood cells

  The white cells are your defenders against infection. There are several different kinds of white cell, and each of them specialise in defending you from a particular infection.

  We have a resting level of white cells in our blood. They simply circulate and ensure our body is defended against infection. If you develop an infection - say appendicitis - the white cells that specialise in that kind of infection will suddenly increase. If you do a blood test it will show "a raised white cell count". So a Doctor can tell from a blood count if you have had an infection, and is given a clue as to what kind of infection by the type of white cell that has increased in number.

• Platelets

  Platelets are tiny cells that circulate in our blood. They are odd shaped. They play an essential role in clotting of out blood. If you cut yourself, you bleed. You bleed red cells and white cells and platelets. The platelets now come into action. Within the platelets are special chemicals which start clotting and stop the bleeding. The platelet breaks up and gives out these chemicals. The FBC simply counts the number of platelets. There are conditions of too few or too may platelets.

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Blood tests