roseola (This is the other test always done to check for anemia.) White blood cell count. White blood cells play a role in the body's defense against infection. Too many or too few of these cells in the blood may indicate an infection or a disorder. To count the white blood cells, a blood specimen is diluted and put in a counting chamber, which is a slide with a grid on it. The slide is examined under a microscope, and the cells are counted. This test can be done in most doctors' offices. Differential blood cell count. There are five different types of normal white blood cells; each type has a distinctive shape and appearance, and each one has a different function. To get more precise information about a disease, the doctor may need to know how many of each type of white blood cells are present in the blood. To do this, a stain is added to a blood specimen; because the stain affects each type of white blood cell differently, it is then easier to tell them apart. The stained specimen is examined under a microscope, and at least 100 white blood cells are identified and classified. The cells are also examined to see if they have a normal shape. In the course of this test, the red blood cells can also be counted and checked for abnormalities. Sedimentation rate. The sedimentation rate reflects the speed at which red blood cells move through the blood and settle in the bottom of a container. To test the rate of settling, a chemical is added to a blood sample to keep it from clotting. Then the red cells are timed as they move to the bottom of a specially marked test tube. This test is used to screen for diseases. A rapid sedimentation rate is a sign of disease, but the test does not identify what is causing the cells to fall more quickly than normal. Keeping track of the sedimentation rate in successive tests can help a physician follow the progress of diseases that cause inflammation, including rheumatic fever and rheumatoid arthritis. THROAT CULTURES A throat culture is done to find out if a throat infection is being caused by bacteria and, if so, to identify the specific type of bacterium. This can provide the doctor with important information. If the infection is due to a virus rather than to a bacterium, the doctor will know not to prescribe antibiotics (viruses don't respond to antibiotics): if a bacterium is the cause, knowing which one it is will enable the doctor to prescribe the correct antibiotic to combat it. To collect material for the culture, the doctor uses a cottontipped swab to remove cells and discharge from the throat. This material is put into a growth medium (a special substance that encourages bacteria to grow). The specimen is watched carefully, and the bacteria are identified. Because throat cultures are often sent to a laboratory for analysis, it may take 48 hours to get the results. OTHER CULTURES Although throat cultures are the most commonly performed, cultures can also be made from blood, bowel movements, and urine, as well as from discharge coughed up from the lungs or obtained from an infected eye or ear or an infected cut or wound. foot and mouth