Primary hyperparathyroidism

Intact parathyroid hormone is mildly elevated (results repeated below) in a setting of markedly elevated calcium and depressed phosphate. At this calcium level, PTH should be significantly suppressed and even a mild elevation is consistent with a diagnosis of primary hyperparathyroidism.

                             Patient         Reference
PTH, intact molecule (P)    56 pg/ml            9 - 51
Calcium, total (S)        13.6 mg/dl        8.4 - 10.1
Calcium, ionized (S)       6.9 mg/dl         4.4 - 5.5

A portion of serum calcium is bound, primarily to albumin. Ionized (free) calcium is responsible for the physiological effects of the ion, and a direct measurement of this fraction may be useful in settings in which calcium binding may be abnormal. However, total serum calcium provides adequate data under most conditions when serum albumin is normal.

Clinical course

Exploratory surgery of neck yielded a large solitary parathyroid adenoma. Calcium levels declined postoperatively and the psychotic symptoms subsided. The patient was discharged on 5th postoperative day.

Notes

In secondary hyperparathyroidism, PTH is elevated in the setting of decreased serum calcium (e.g., in renal failure).

There are several versions of the PTH assay. C-terminal, mid-molecule, and N-terminal assays are older tests that measure metabolic fragments of PTH. Some of these tests may provide misleading data under certain circumstances; for example, C-terminal PTH is markedly elevated in renal failure without hyperparathyroidism due to the decreased clearance of the long-lived C-terminal fragment of PTH. Tests are now generally available that specifically measure the intact PTH molecule. These tests should be used for most parathyroid workups.