Blood count

The large blood count consists of the small blood count and the differential blood count. In it, the leukocytes are broken down into their subgroups. Leukocytes are called white blood cells because they have no blood pigment. As part of the immune system, they play a role in both specific and non-specific immune defence. They are involved in infections, inflammations, allergic reactions and autoimmune diseases. Leukocytes make up only 1 per cent of blood cells. When their number is decreased, it is called leukopenia; when it is increased, it is called leukocytosis. Changes in leukocytes indicate a disturbed or activated immune defence. Leukocytes include granulocytes, monocytes and lymphocytes. In order to determine the respective proportions, a blood smear is stained. The percentages are determined from 100 counted leucocytes. The granulocytes are divided into the subgroups neutrophils, eosinophils and basophils depending on the staining of their granules.

Up to 45 percent of leukocytes are lymphocytes. They split into T-lymphocytes and B-lymphocytes. T-lymphocytes become T-helper cells and cytotoxic T-cells after they have had antigen contact. T-helper cells stimulate the immune defence, cytotoxic T-cells destroy foreign and tumour cells. B-lymphocytes develop into antibody-producing plasma cells after antigen contact. The lymphocyte count is increased, as is the eosinophil count, when an infection is subsiding.