Complete Blood Count (CBC)

A complete blood count (CBC) is a common blood test that measures the different cells in your blood, including red blood cells, white blood cells, and platelets. It gives your health care provider important information about your overall health.

The 17-Hydroxyprogesterone (17-OHP) test measures the amount of a specific steroid hormone in your blood. This test is done BEFORE (the 'pre' in the name) you receive an injection of 250 micrograms of corticotropin (ACTH). ACTH is a hormone that tells your adrenal glands to produce cortisol and other hormones. By measuring 17-OHP before the ACTH injection, doctors can see how well your adrenal glands are working and check for certain conditions.

You might need this test as part of a routine checkup, or to help find the cause of symptoms such as fatigue, weakness, fever, easy bruising, or unusual bleeding. It can also help your provider monitor an ongoing condition or check how well a treatment is working.

Your doctor may order this test if they suspect you have a problem with your adrenal glands. Common reasons include: checking for congenital adrenal hyperplasia (CAH), a genetic condition affecting hormone production; evaluating adrenal insufficiency (when your adrenal glands don't produce enough hormones); investigating symptoms like early puberty, irregular periods, or excessive hair growth; and monitoring treatment for adrenal conditions.

In most cases, no special preparation is needed for a CBC. You can usually eat and drink normally before the test. Tell your provider about all medicines, vitamins, and supplements you take, since some can affect the results. If other blood tests are done at the same time, you may be asked to fast for a few hours beforehand.

Your doctor will give you specific instructions. Generally, you may need to: fast (not eat or drink except water) for 8-12 hours before the test; tell your doctor about all medications you're taking, especially steroids or birth control pills; avoid strenuous exercise before the test; and follow any other instructions your healthcare provider gives you.

During the test, a health care professional will clean the skin on your arm, wrap a band around your upper arm, and draw a small sample of blood from a vein, usually on the inside of your elbow. The needle stick lasts only a few seconds, and the entire process usually takes less than ten minutes.

A healthcare professional will draw a small blood sample from a vein in your arm using a needle. This is called a venipuncture. The blood sample is collected into a special tube and sent to a laboratory for analysis. After this first blood draw, you will receive an injection of corticotropin (ACTH), and additional blood samples may be taken at later time points to see how your adrenal glands respond. This is called an ACTH stimulation test.

A CBC is very safe. The most common side effects are brief pain and slight bruising or bleeding where the needle was inserted. Some people feel lightheaded during a blood draw. Serious problems, such as infection or heavy bleeding, are rare.

The risks of a blood draw are minimal and include slight pain or bruising at the injection site, lightheadedness, and rare risk of infection. The ACTH injection may cause temporary flushing, increased heart rate, or mild discomfort. Serious reactions are rare. Talk to your doctor if you have concerns.

Results are usually ready within one to two days. Your provider will review the numbers with you and explain what they mean for your health. If any value looks unusual, your provider may order follow-up tests or schedule a visit to discuss the next steps.

The time it takes to get results varies by laboratory. It usually takes 1-3 days. Your doctor will contact you with the results and explain what they mean for your health.