The two most common blood tests are a complete blood count (CBC)—which measures the number of red blood cells, white blood cells, and platelets in the blood—and a basic metabolic panel (BMP). These screen for a variety of illnesses including: anemia, diabetes, kidney disease, liver disease, and an imbalance of certain minerals like sodium, potassium, and calcium (electrolytes). Two other frequently ordered tests will measure your cholesterol level and the function of your thyroid gland.

Blood tests can be performed on different parts of the blood, including:

• Whole blood (blood that has not been separated into its many components)

• Blood plasma (the liquid part of the blood)

• Blood serum (plasma that has had the clotting agent removed)

• Blood cells (the individual red blood cells, white blood cells, and platelets)

To get your blood flowing well, drink eight to ten glasses of liquid the day before and day of your test. It also makes the veins more likely to stick up and be found easily, so drink up for a day or two before your test. But remember to follow your doctor’s instructions—some tests require that you not drink certain liquids prior to the test or that you avoid eating anything during the six hours before blood is drawn.