General type of medical test that involves taking samples of urine, blood, saliva, stool, and other fluids, waste, and tissue from the body for analysis. The characteristics of normal body substances are well known, so laboratory analysis can indicate if the patient’s sample is markedly different from the norm and, if so, in what ways. If blood is removed by inserting a needle into a vein and withdrawing it into a syringe or a catheter, the procedure is called venipuncture. If a fluid sample is taken from the body using a hollow aspiration needle, the procedure is called centesis, as in the prenatal test called amniocentesis. If a tissue sample is taken from the body, often using a similar hollow needle, the procedure is called a biopsy.