This test evaluates the blood count by critical examination of the blood smear. Blood is composed of several different types of cells. This test is used to analyze the complete blood count. This test detects numerous conditions which cause decline in blood population. Anaemia, myeloproliferative neoplasm, bone marrow disorders and leukemia are major disorders on list which cause low blood cell density in body. There are basically three types of blood cells in the human system. These include red blood cells, white blood cells and platelets. Deficiency of any of these has different impact on body corresponding to the functions they perform.