Blood count (small and full blood count)

The blood count is a count and measurement of the blood cells in EDTA whole blood. The small blood count covers the red blood cells (erythrocytes), the red blood pigment haemoglobin, the share of cells in the blood volume (haematocrit), the red cell indices MCV, MCH and MCHC calculated from these, and the total number of white blood cells (leucocytes) and platelets (thrombocytes). The full blood count adds the differential blood count: it breaks the leucocytes down into their subgroups – neutrophil, eosinophil and basophil granulocytes, lymphocytes and monocytes. In this way the blood count shows how the bone marrow is working and how the body responds to blood loss, nutrient deficiency or inflammation.

What the cells in the blood count do in the body

Erythrocytes use their haemoglobin to carry oxygen from the lungs to all tissues and carbon dioxide back. To make them in the bone marrow, the body needs iron, vitamin B12 and folic acid; the kidney hormone erythropoietin controls the amount. MCV describes the size of the individual cell, MCH its haemoglobin content – this shows whether iron or rather vitamin B12 and folic acid are lacking. Leucocytes are the immune cells: neutrophils fight mainly bacteria, lymphocytes fight viruses and control antibody production, eosinophils respond to parasites and allergies, and monocytes clear up as scavenger cells. Platelets attach to the vessel wall when an injury occurs and start blood clotting.

Low blood count values – what happens in the body?

When haemoglobin and erythrocytes fall, less oxygen reaches the tissues. The heart beats faster to compensate for the shortfall; pallor, rapid exhaustion, breathlessness on exertion and difficulty concentrating follow. Small, pale cells (low MCV and MCH) typically arise with iron deficiency, for example due to blood loss or impaired absorption in the gut; large cells point to too little vitamin B12 or folic acid. Few leucocytes mean weaker defences – infections occur more often or take longer to clear. This happens with some viral infections, with certain medicines or with disorders of the bone marrow. When platelets are lacking, blood clots more slowly: bruises, nosebleeds and pinpoint skin bleeding occur more easily.

High blood count values – what happens in the body?

Many erythrocytes and a high haematocrit make the blood thicker; it flows more slowly through the fine vessels. This occurs with dehydration, smoking, stays at high altitude or chronic lack of oxygen, to which the kidney responds with more erythropoietin; less often the bone marrow itself makes too many cells. Raised leucocytes usually show that the immune system is working: with bacterial infections mainly the neutrophils rise, with viral infections the lymphocytes, with allergies and parasites the eosinophils. Stress, smoking and cortisone also increase the count. Platelets rise with inflammation, iron deficiency and after blood loss, because the bone marrow responds to the same signals; the blood then clots more readily.

The interpretation is given in your report.