In Clinical Medicine, choosing the appropriate diagnostic tests and interpreting the results knowledgeably is often the difference between success and failure, especially when treating seriously ill patients. Many of the newer diagnostic tests have had a dramatic effect on patient care. The work of the clinical laboratory personnel who analyzes many things in the body including chemical indicators, the health of blood cells, and the presence of microbes and genetic markers has long been an unseen aspect of healthcare. Yet, clinical lab tests often provide the link between the patient's presentation of symptoms and the doctor's diagnosis of and prescribed treatment for a particular condition or disease. Through preventive screening, lab tests also aid in the early detection of potentially fatal conditions, and in so doing, lead to early treatment. In short, lab tests can help both to save lives and to improve the quality of life.