Rapid radioimmunoassay for parathyroid hormone: its use in hypercalcemic crisis

Patients with severe hypercalcemia often require intensive medical therapy to avoid a fatal outcome. When therapy with saline and loop diuretics cannot control the hypercalcemia, use of the toxic drug mithramycin is most appropriate for malignancy-associated hypercalcemia, but parathyroidectomy is indicated for parathyroid crisis. Although differentiation of these two syndromes is possible in many cases on clinical grounds, the determination of immunoreactive parathyroid hormone values provides a direct assessment of parathyroid function. Radioimmunoassay for parathyroid hormone has traditionally required four to seven days, but more rapid results would be desirable in this medical emergency. We report a modification of a previously published midregion-specific PTH assay that provides accurate results within 24 hours and describe its use in six patients with life-threatening hypercalcemia.