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Parathyroid hormone, commonly known as PTH, is a crucial hormone produced by the parathyroid glands, which are four small glands located behind the thyroid gland in the neck. This hormone plays a vital role in regulating calcium and phosphorus levels in the blood and bones. When blood calcium levels drop too low, the parathyroid glands release PTH to restore balance. The hormone works by stimulating the release of calcium from bones, increasing calcium absorption in the intestines, and reducing calcium loss through the kidneys. Additionally, PTH activates vitamin D, which further helps the body absorb calcium from food.

A PTH blood test is ordered when healthcare providers suspect problems with calcium metabolism or parathyroid gland function. Common reasons for testing include abnormal calcium levels detected in routine blood work, symptoms of high calcium such as kidney stones, bone pain, excessive urination, or fatigue, and symptoms of low calcium including muscle cramps, tingling sensations, or seizures. The test may also be used to monitor patients with known parathyroid disorders, chronic kidney disease, or those who have undergone parathyroid surgery. It is often performed alongside calcium and vitamin D tests to provide a complete picture of calcium regulation in the body.

The PTH test requires a simple blood sample, typically drawn from a vein in the arm. Patients may be asked to fast for several hours before the test, as food intake can affect results. The blood sample is usually collected in the morning since PTH levels can vary throughout the day. Some medications and supplements, particularly those containing calcium or vitamin D, may need to be temporarily discontinued before testing, so patients should inform their healthcare provider about all medications and supplements they are taking.

Normal PTH levels typically range from 10 to 65 picograms per milliliter, though reference ranges may vary slightly between laboratories. Elevated PTH levels combined with high calcium suggest primary hyperparathyroidism, often caused by a benign tumor on one of the parathyroid glands. High PTH with low or normal calcium may indicate secondary hyperparathyroidism, commonly seen in chronic kidney disease or vitamin D deficiency. Low PTH levels with high calcium suggest hypoparathyroidism, which can result from surgical damage to the parathyroid glands, autoimmune conditions, or genetic disorders. Interpreting PTH results requires careful consideration of calcium levels, vitamin D status, kidney function, and clinical symptoms to determine the underlying cause and appropriate treatment.