Question: I'm on birth control pills. Can testing for Cushing's be done while I'm on the pill and if not, how long before testing do I need to stop taking them?

Answer: Birth control pills will affect the testing done in the evaluation of Cushing's syndrome. The estrogens in the birth control pills will increase a blood protein called cortisol binding globulin, which acts like a sponge to hold onto cortisol. When the amount of cortisol binding globulin increases, the total amount of cortisol that is measured will increase as well. This may, in some circumstances, lead to a false diagnosis of hypercortisolemia, or Cushing's syndrome. There are several ways around this problem. First, a 24 hour urine collection for cortisol can be performed, because changes in cortisol binding globulin do not significantly affect the urinary measurement. If blood cortisol levels need to be measured, then it is important to stop all estrogen supplements, such as birth control pills for at least six weeks before further testing is performed.