Some healthy adult volunteers will have hormone-stimulating tests to assess endocrine function. These tests measure blood hormone levels before and after injection of a synthetic form of a hormone. A device called a heparin lock, through which the hormone is injected and the blood samples are collected, is placed in a vein in the arm or hand. Blood samples are drawn before the hormone is injected and at various intervals after the injection to measure levels of the hormone. These tests, which last from 1 to 3 hours, may include the following: