What Is the ACTH Stimulation Test?

ACTH, also called cosyntropin, causes the adrenal glands to release cortisol into the bloodstream. An ACTH stimulation test is used to measure how well the adrenal glands react when stimulated by ACTH that is injected into the patient. The results from this test help to diagnose such health problems as Addison’s disease or the presence of pituitary tumors.

The ACTH stimulation test measures the amount of cortisol that is present in the blood. Levels are checked at the beginning of the test, and then again an hour after the ACTH injection. Before the ACTH is injected, blood is drawn from a vein in the crook of the arm. For infants and very young children, a lancet is used to make a tiny wound so that a few drops of blood can be collected for the test. This first blood sample is used to determine the base levels of cortisol.

ACTH is then injected. Once 60 minutes has passed another blood collection is done, and the cortisol levels are checked to determine how the adrenal glands have responded. Low levels of cortisol indicate diminished functioning of the adrenal glands and could be indicative of Addison’s disease or another deficiency of the adrenal glands. Very high levels could be indicative of other serious problems and require further investigation. A urinalysis may also be done in conjunction with the ACTH stimulation test.

In order for the results of the ACTH stimulation test to be valid, it is important for the patient to prepare in advance. The general guidelines require the patient to limit activity for 24 hours prior to the test, avoiding strenuous exercise such as jogging, cycling and tennis. Second, he or she should eat a high carbohydrate diet the day before the test. In some cases the patient may be asked to fast the last few hours before the test is administered. Complying with all of these requirements helps to ensure valid results from the ACTH stimulation test.

If a person has abnormal results from the ACTH stimulation test, additional testing will be done to determine the exact reason for the problem. Imaging such as a computerized tomography (CT) scan of the adrenal glands is common, and a magnetic resonance imaging (MRI) scan may be used to identify trouble with the pituitary gland. Blood tests and insulin testing may be done as well, all with the ultimate goal of diagnosing the problem quickly and helping the patient return to health in as short a time as possible.