Parathyroid Hormone (Active), Serum

Your doctor may order this test to check how well your parathyroid glands are working and to help find the cause of abnormal calcium levels in your blood. The active PTH test measures the portion of parathyroid hormone that is biologically active in your body. It is often used to evaluate symptoms such as fatigue, bone pain, kidney stones, or unexplained high or low calcium, and to monitor people with known parathyroid or kidney conditions.

Your doctor may order this test if you have symptoms like muscle weakness, frequent bone fractures, or abnormal calcium levels. It’s also used to evaluate conditions such as kidney disease, vitamin D deficiency, or thyroid disorders that can affect PTH levels.

Before the test, tell your healthcare provider about all medicines, vitamins, and supplements you take, because certain drugs can affect PTH and calcium levels. You may be asked to avoid eating for several hours, and a morning blood draw is often preferred. Drink water unless instructed otherwise, and wear clothing with a sleeve that can be rolled up easily. Your provider will explain any specific preparation steps that apply to you.

No special preparation is needed. You’ll provide a blood sample, usually drawn from a vein in your arm. If you’re on certain medications (like calcium supplements or vitamin D), let your doctor know beforehand.

This test is performed on a small sample of blood, usually drawn from a vein in your arm. In the laboratory, the sample is analyzed to measure the amount of biologically active parathyroid hormone circulating in your blood. Because PTH levels naturally rise and fall with your body's calcium balance, the result is typically reviewed together with your calcium level to give a complete picture of how your parathyroid glands are functioning.

Blood is drawn and tested for the active form of PTH using a sensitive immunoassay method. This measures the hormone’s ability to stimulate bone cells and kidneys to release calcium.

Results are reported as a numeric value compared with a reference range provided by the laboratory. A high active PTH level may point to overactive parathyroid glands, vitamin D deficiency, kidney disease, or the body's response to low calcium. A low level may suggest too much calcium in the blood or reduced parathyroid function. Your healthcare provider will interpret your result alongside your symptoms, calcium levels, and medical history to determine what it means for you.

Results are compared to a reference range, but exact values can vary by lab. Low levels may indicate hypoparathyroidism, while high levels could suggest hyperparathyroidism or other metabolic issues.