What Is Parathyroid Hormone Testing?

Parathyroid hormone testing evaluates the levels of parathyroid hormone (PTH) in the blood or in the actual gland. One type of test is comprised of a blood draw and laboratory analysis, and this may be done when people have symptoms of high calcium levels or other indications of parathyroid problems. A second test, called the intraoperative PTH, only takes place during a surgery to remove part of the parathyroid glands, and is much less common. Either analysis seeks to discern whether PTH is too high or low, which helps guide treatment.

Both the parathyroid hormone and the glands that release it play an important role in the body’s functioning. PTH helps regulate calcium levels in the blood by removing calcium from bone and reducing the amount of the mineral that is excreted from the kidneys. If too much or too little PTH is produced, blood levels of calcium may rise dangerously or they could drop far below normal. Since hyperparathyroidism and hypoparathyroidism can cause pronounced health issues, analysis of PTH is sometimes necessary.

Patients who have parathyroid hormone testing are most likely to go to a doctor or laboratory for a simple blood collection. Many labs ask people not to eat for 10-12 hours prior to the test, and they may prefer to draw the blood in the early morning because PTH levels fall during the day. A normal reading is between 10-55 picograms, or one trillionth of a gram, per milliliter of blood, and sometimes tests that fall slightly above or below these numbers may still be considered normal.

One of the most frequent indications to perform parathyroid hormone testing of this type is if an individual has higher or lower than normal blood calcium levels. Unusual phosphorous or vitamin D levels could also be reasons for testing, and certain health conditions like kidney failure may warrant performing this test, too. The basic goal with parathyroid testing is to determine if a person may have hyperparathyroidism or hypoparathyroidism, and to use that diagnosis to further investigate the cause of the problem.

Often, physicians order a panel of tests that simultaneously evaluate vitamin D, calcium, phosphorous, and PTH. Other blood tests to look at kidney function might be performed, too. Analyzing a series of tests and comparing them to any patient symptoms may help narrow down the cause of the problem.

In some instances, an outside factor like kidney failure causes dysfunction of the parathyroid glands. Alternately, the glands may be solely responsible for high or low PTH levels. When this is the case, surgeons may opt to remove one or more glands to improve PTH function. In these scenarios, intraoperative parathyroid hormone testing may be necessary.

Simple blood collection can’t tell physicians which glands are most affected. In surgery, doctors can use intraoperative parathyroid hormone testing to evaluate each gland and determine which ones should be removed. By assessing the function of the whole parathyroid structure during an operation, surgeons may reduce the necessity of additional surgeries.