The so-called intact PTH is the most frequently ordered parathyroid hormone test. It is used to help diagnose the cause of a low or high calcium level and to help distinguish between parathyroid-related and non-parathyroid-related causes. It may also be used to monitor the effectiveness of treatment when an individual has a parathyroid-related condition. PTH is routinely monitored for people with chronic kidney disease or who are on dialysis.
A calcium test is almost always ordered along with a PTH test. It is not just the level in the blood that is important but the balance between calcium and PTH and the response of the parathyroid glands to changing levels of calcium. Usually, health practitioners are concerned about either severe imbalances in calcium regulation that may require medical intervention or persistent imbalances that indicate an underlying problem.
PTH levels can be used to monitor people who have conditions or diseases that cause chronic calcium imbalances or to monitor those who have had surgery or another treatment for a parathyroid tumor.
A PTH test may be ordered when a test for calcium is abnormal. It may be ordered when someone has symptoms associated with hypercalcemia, such as:
PTH may also be ordered when a person has symptoms associated with hypocalcemia, such as:
Tingling fingers or toes
A health practitioner may order a PTH test along with a calcium test at intervals when someone has been treated for a disease or condition that affects calcium regulation, such as the removal of a parathyroid tumor, or when a person has a chronic condition such as kidney disease.
Sometimes, an intraoperative PTH test will be ordered when someone who has hyperparathyroidism is undergoing surgery to have abnormal parathyroid tissue removed to ensure removal of all of the abnormal glands, which can occasionally vary in number and location.
A health practitioner will evaluate both calcium and PTH results together to determine whether the levels are appropriate and are in balance as they should be. If both PTH and calcium levels are normal, then it is likely that the body's calcium regulation system is functioning properly.
Low levels of PTH may be due to conditions causing hypercalcemia or to an abnormality in PTH production causing hypoparathyroidism. Excess PTH secretion may be due to hyperparathyroidism, which is most frequently caused by a benign parathyroid tumor. In rare cases, it may be caused by cancer.
The table below summarizes results that may be seen:
Calcium regulation system functioning OK
PTH is responding correctly; may run other tests to check for other causes of hypocalcemia
Normal or Low
PTH not responding correctly; probably have hypoparathyroidism
Parathyroid gland producing too much PTH; may do imaging studies to check for hyperparathyroidism
PTH is responding correctly; may run other tests to check for non-parathyroid-related causes of elevated calcium
Calcium - PTH Relationship
If calcium levels are low and PTH levels high, then the parathyroid glands are responding appropriately, producing appropriate amounts of PTH. Depending on the degree of hypocalcemia, a health practitioner may investigate a low calcium level further by measuring vitamin D, phosphorus, and magnesium levels.
If calcium levels are low and PTH levels are normal or low, then PTH is not responding properly and the person tested probably has hypoparathyroidism. Hypoparathyroidism is a failure of the parathyroid glands to produce sufficient PTH. It may be due to a variety of conditions and may be persistent, progressive, or transient. Causes include an autoimmune disorder, parathyroid damage or removal during surgery, a genetic condition, or a severe illness. Those affected will generally have low PTH levels, low calcium levels, and high phosphorus levels.
If calcium levels are high and PTH levels are high, then the parathyroid glands are producing inappropriately high amounts of PTH. A health practitioner may order X-rays or other imaging studies to help determine the cause and evaluate the severity of hyperparathyroidism. Hyperparathyroidism is a group of conditions characterized by an overproduction of PTH by the parathyroid glands that is separated into primary, secondary, and tertiary hyperparathyroidism. [See Parathyroid Diseases for more on this.]
If calcium levels are high and PTH levels are low, then the parathyroid glands are responding properly, but a health practitioner is likely to perform further investigations to check for non-parathyroid-related reasons for the elevated calcium, such as rare mutations in calcium receptors or tumors that secrete a peptide that has PTH-like activity and increases calcium concentration, which in turn decreases PTH.
Currently, the most prevalent assay for PTH is the intact PTH assay, which typically measures the whole molecule (PTH 1-84) and the larger fragments (predominantly PTH 1-74). While this assay is known as the "intact" assay, it measures large fragments that are slightly smaller than the truly intact hormone. There are less common but newer assays that detect only the whole molecule, which has the greatest bioactivity. The "intact" and "whole or bioactive" assays have different reference ranges, but typically their results yield similar interpretations. The effects of fragmentation and disease are still being studied, and there are instances when the two assays may yield a different interpretation.
Drugs that may increase PTH levels include phosphates, anticonvulsants, steroids, isoniazid, lithium, and rifampin.
This article was last reviewed on March 6, 2014. | This article was last modified on February 24, 2015.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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