Behind the thyroid gland in the neck are four small parathyroid glands that secrete parathyroid hormone (PTH), also known as parathormone PTH), into the bloodstream. The hormone is important in helping the body maintain the proper level of circulating calcium. Without PTH, a calcium imbalance can affect heart function, muscle contraction, nerve signaling, and blood clotting.

Physicians use PTH to diagnose parathyroid problems including hyperparathyroidism and hypoparathyroidism. The former leads to abnormally low calcium levels while the latter causes dangerously high calcium levels. Physicians often order calcium and vitamin D levels at the same time as PTH. Vitamin D helps the body absorb dietary calcium. If vitamin D is not ordered, the physician may not be able to tell if the patient's abnormal calcium level in the blood is caused by a dysfunctional parathyroid gland or a problem absorbing calcium in the diet.

PTH is sometimes, but not always, ordered as a fasting test. Although it can be tested on serum or plasma from an EDTA tube, serum sample are unstable and must be immediately placed in an ice slurry before leaving the patient, then centrifuged at refrigerated temperatures. If it cannot be tested immediately, serum should be frozen. If collected into an EDTA tube, however, it remains stable in whole blood for at least 24 hours at room temperature (two days, according to some studies).

Bibliography

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