Blood count is a test to determine the number of red and white cells and the amount of hemoglobin, the oxygen-carrying protein, in the blood. A laboratory technician usually obtains blood for the test by pricking a person’s finger or by taking blood from a vein with a needle. The technician mixes the blood with a solution to keep it from clotting. The technician uses an electronic counter to determine the cell counts and hemoglobin measurements. The technician then spreads a thin film of blood onto a piece of glass and stains it. Using a microscope, the technician determines the percentage of different types of red and white blood cells on this glass. Too many white cells may indicate an infection. Too few cells or the presence of abnormal cell types may mean the blood-forming bone marrow is damaged. The color of the blood, which reflects the amount of hemoglobin and number of red cells, may indicate anemia (see Anemia ). See also Hemoglobin .
