Complete Blood Count (CBC)

A complete blood count, or CBC, is a common blood test that measures the different cells in your blood, including red blood cells, white blood cells, and platelets. These cells carry oxygen, fight infection, and help your blood clot properly, so this test gives your doctor a broad picture of your overall health.

The 17-Hydroxyprogesterone (17-OHP) test measures the amount of a specific hormone called 17-hydroxyprogesterone in the blood. This hormone is produced by the adrenal glands, which sit on top of each kidney. The test is primarily used as a screening tool to detect a condition called congenital adrenal hyperplasia (CAH) in newborns, though it may also be used in older children and adults when CAH is suspected.

Your doctor may order a CBC as part of a routine checkup or to help investigate symptoms such as fatigue, weakness, fever, bruising, or unexplained bleeding. It is also used to monitor an ongoing condition or to check how a treatment, such as chemotherapy, is affecting your blood cells over time.

The main purpose of the 17-OHP test is to screen newborns for congenital adrenal hyperplasia (CAH). CAH is a group of genetic disorders that affect the adrenal glands' ability to produce cortisol, a stress hormone, and aldosterone, which helps regulate salt and water balance in the body. Without early detection and treatment, CAH can lead to serious complications including adrenal crisis, salt-wasting crises, abnormal puberty, and growth problems.

The test is done with a simple blood draw. A healthcare professional cleans a spot on your arm, usually the inside of your elbow, wraps a band around your upper arm, and collects a small sample of blood into a tube. The procedure takes only a few minutes, and you can return to your normal activities right afterward.

For newborns, a small blood sample is collected by pricking the baby's heel, similar to other routine newborn screening tests. The blood is placed on a special filter paper card and sent to a laboratory for analysis. In older children or adults, a blood sample is drawn from a vein in the arm. The test requires no special preparation such as fasting.

Your results show whether your blood cell counts fall within the normal range. High or low values can point to conditions such as anemia, infection, inflammation, or clotting problems. Your doctor will interpret the numbers together with your symptoms and medical history, since a single abnormal value does not always mean a serious problem.

Normal 17-OHP levels vary depending on the baby's age, weight, and whether they were born prematurely. Elevated levels of 17-OHP may indicate congenital adrenal hyperplasia, but further testing is needed to confirm the diagnosis. Very high levels are more likely to indicate classic CAH, while mildly elevated levels may require repeat testing or additional evaluation to rule out false positives or other conditions.