MODEL RELEASED. Blood count. Laboratory assistant carrying out a blood count, using an electron microscope. A sample of blood is taken from a patient and an anticoagulant is added to a known volume of the sample. A count is then made of the number of red cells, white cells and platelets present. This can be done by eye, as here, or using an electronic cell counter. The results are expressed as the number of a specific cell type per litre. Blood counts are important in the diagnosis of blood disorders, such as anaemia.