Complete Blood Count (CBC) Test Overview

A complete blood count (CBC) is a routine blood test that measures the cells that make up your blood, including red blood cells, white blood cells, hemoglobin, hematocrit, and platelets. It gives your healthcare provider a broad picture of your overall health.

The 17-Hydroxyprogesterone (17-OHP) challenge test measures the level of 17-hydroxyprogesterone in your blood 2 hours after receiving an injection of ACTH (adrenocorticotropic hormone). ACTH is a hormone that stimulates your adrenal glands to produce other hormones, including cortisol and androgens. This test evaluates how well your adrenal glands are functioning.

This test is performed to evaluate your general health, screen for conditions such as anemia, infection, and blood disorders, and to monitor an existing medical condition or track how treatments like chemotherapy or certain medications are affecting your blood cells.

This test is primarily used to diagnose and monitor congenital adrenal hyperplasia (CAH), a genetic disorder affecting the adrenal glands' ability to produce cortisol. It may also be used to evaluate adrenal insufficiency and distinguish between different types of adrenal disorders. Your doctor may order this test if you or your child show symptoms such as early puberty, irregular periods, excessive hair growth, or ambiguous genitalia.

The test is done by drawing a small sample of blood, usually from a vein in the inside of your elbow or the back of your hand. A healthcare professional cleans the site, inserts a thin needle, collects the blood into a tube, and applies pressure and a bandage afterward. The sample is then sent to a laboratory for analysis.

The test requires two blood samples. First, a baseline blood sample is taken to measure your initial 17-OHP level. Then, you will receive an injection of synthetic ACTH (cosyntropin). After exactly 2 hours, another blood sample is collected. The time interval is important because it allows the ACTH to stimulate your adrenal glands and peak hormone levels to be measured.

In most cases, no special preparation is needed for a CBC, and you can usually eat and drink normally beforehand. Tell your healthcare provider about all medicines, vitamins, and supplements you take, and mention if you have ever felt faint during a blood draw or if you bruise or bleed easily.

Your doctor will provide specific instructions. Generally, you may need to fast (not eat or drink except water) for 8-12 hours before the test. Certain medications, especially corticosteroids and hormone treatments, may affect results and should be discussed with your doctor. Inform your healthcare provider about all medications, supplements, and herbal remedies you are taking.

Your results will show whether your blood cell counts fall within the normal range. A low red blood cell count may suggest anemia, while a high white blood cell count can point to infection or inflammation. Abnormal platelet levels may affect how your blood clots. Your healthcare provider will interpret the values together with your symptoms and medical history to explain what they mean for you.

Normal results vary by age and gender. Elevated 17-OHP levels after ACTH stimulation typically indicate congenital adrenal hyperplasia or other adrenal enzyme deficiencies. Your doctor will interpret your results alongside your symptoms and other test findings. A definitive diagnosis may require additional testing or genetic testing.