Most common tests are painless or cause only brief discomfort, such as a pinprick or needle puncture. Others can cause cramps, nausea, headache, or serious discomfort. In these cases, part of the test may involve administering a sedative, or local or general anesthesia. Side effects may last hours or longer, or may only be felt by some patients and not by others. This is the most important question.
Many common tests have no risks at all.
Others have risks that may range from transitory side effects to more serious problems. Invasive tests, that is, those that involve introducing instruments or substances such as barium into the body, generally have some risks. These may include infection, allergic reaction, or injury to the body, either at the site of the incision or to an internal organ. This will help the patient to decide whether the risk is one that must be borne because the consequences of an undiagnosed illness may be worse.