Why Are Clinical Laboratory Tests Performed? When Are They Valid?

TODAY, more than 2 billion medical laboratory tests are performed each year in the United States, at an annual cost that exceeds 6 billion. Three times this volume is predicted for 1980. Does this high utilization indicate better patient care at lower cost through modern medical science? And will the projected increase to 6 billion tests per year by 1980, at an annual cost of 20 billion, represent further progress toward better health? The answer is, not necessarily. Why do physicians request laboratory tests? Some results—of blood gas, glucose, and electrolyte determinations—are needed to monitor and guide treatment of critically ill patients. Other results—as from creatinine and thyroxine tests—help us to detect early renal or thyroid disease. Still other tests appear to be done primarily because they are available. But in all cases, the usefulness of a positive test result will vary with the sensitivity and specificity of the test,