Understanding Your Laboratory Test: What It Is, How It Is Done, and What to Expect

This test is a diagnostic procedure that gives your healthcare provider important information about your health, such as how well certain organs are working or whether an illness or other condition may be present.

The 17-Hydroxyprogesterone (17-OHP) Stimulation Test is a specialized blood test that measures how your body responds to a hormone called Adrenocorticotropic Hormone (ACTH). ACTH is produced by the pituitary gland and tells your adrenal glands to release cortisol and other hormones. By giving you synthetic ACTH and measuring your 17-OHP response, doctors can evaluate how well your adrenal glands are working and check for certain disorders.

How the test is performed depends on the type ordered. Most laboratory tests involve collecting a small sample of blood, urine, or other body fluid, while imaging tests use special equipment to create pictures of the inside of your body.

The test typically takes 1-2 hours and involves several steps: First, a healthcare provider will insert an intravenous (IV) line into your arm. A baseline blood sample (before the stimulation) is taken. Then, synthetic ACTH (called cosyntropin or Synacthen) is injected through the IV. Exactly 1 hour after the injection, another blood sample is collected. Some variations may include additional samples at 30 or 60 minutes. The samples are sent to a laboratory to measure 17-hydroxyprogesterone levels.

Your provider may order this test to help diagnose a medical condition, check how well a treatment is working, screen for disease before symptoms appear, or monitor an ongoing health problem over time.

Doctors order this test primarily to help diagnose and distinguish between different types of adrenal gland disorders, most commonly congenital adrenal hyperplasia (CAH). CAH is a genetic condition that affects the adrenal glands' ability to produce cortisol and sometimes aldosterone. The test can also help identify other adrenal disorders, differentiate between adrenal and pituitary causes of hormone deficiencies, and in some cases, evaluate for certain adrenal tumors.

Preparation depends on the specific test you are having. You may be asked to fast for several hours, avoid certain foods or medications, or drink extra water beforehand. Always follow the instructions from your provider or the laboratory, and ask questions if anything is unclear.

Your doctor will provide specific instructions, but general preparation includes: fasting (not eating or drinking anything except water) for 8-12 hours before the test, informing your doctor about all medications you're taking as some drugs can affect results, telling your doctor if you have any allergies, wearing comfortable clothing with easy access to your arms, and scheduling the test in the morning since hormone levels follow a daily rhythm. Women should inform their doctor about their menstrual cycle as hormone levels can vary throughout the cycle.

Most tests cause little or no discomfort. If a blood sample is taken, you may feel a quick sting when the needle goes in. Imaging tests are usually painless, though you may feel slight pressure or need to hold still for a short time.

You may feel a brief sting when the IV is inserted. The ACTH injection itself is generally well tolerated, but some people may experience temporary flushing, warmth, increased heart rate, or a mild headache. These sensations are usually short-lived. The blood draw at the 1-hour mark may feel similar to the initial draw. Overall, the discomfort is minimal for most patients.