What is a Blood Count?

The blood screen is also known by some well known acronyms including:

FBC = Full Blood Count

CBC = Complete Blood Count

FBS = Full Blood SCreen

FBE = Full Blood Examination.

The major tests that are carried out in a blood screen are: Haemoglobin, Red Cell Count, Packed Cell Volume (or haematocrit), Mean Cell Volume, Mean Cell Haemoglobin, White Cell Count and Platelet Count. Often a differential or White cell differential is included but this will be covered in a separate article.

Haemoglobin (Hb) - Hb is a substance found in the red cells which carries oxygen to the tissues and CO2 back to the lungs. A reduction in Haemoglobin levels is called anaemia. An increased Hb level is known as Polycythaemia (combined with an increased red cell count). The Mean Cell Heamoglobin (MCH) is a measure of the cellular content of Hb.

The Red Cell count- (RCC) is a measure of the numbers of red cells or erythrocytes circulating in the blood. A low red call count is associated with anaemia and a high count with polycythaemia or erythaemia.

The Packed Cell Volume (or haematocrit) is a measure of the proportion of a nominal unit of blood that is composed of Red Cells. This can be measured after spinning a capillary tube filled with blood for 5 minutes at high rpm. On todays blood analysers this value is derived from other measures. A low PCV is seen in anaemia and post blood loss, and a high PCV is seen in polycythaemia and in dehydration.

Mean Cell Volume (MCV) - the mean cell volume is the measure of the average size of a red cell. A decreased MCV is seen in Iron deficiency anaemia and in thalassaemia. An increased MCV is typically seen in B12 and folate deficiency and in alcoholism.

The White Cell Count (WBC) gives an indication of infection or inflammation when high and of bone marrow suppression or overwhelming sepsis when low.

Platelet Count - platelets are crucial in maintaining the bodies haemostasis and vascular integrity. When a cut or damage is made to vessels or tissues, platelets rush to the site of injury and aggregagte into plugs that helps to stop the bleeding. Platelets work together with the bodies clotting factors to stop bleeding. A low platelet count is known as thrombocytopenia and a high count as thrombocythaemia. These words derive from the word thrombocyte which is another name for a platelet.

The Blood Count gives your doctor invaluable information about your health and along with the biochemistry screen is a mainstay of medical diagnosis.