Stimulation of parathyroid hormone secretion by EDTA infusion – a test for the differential diagnosis of hypercalcaemia

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Abstract
A constant EDTA infusion of 24 mg/kg/h during 60–120 min was given to 26 patients with primary hyperparathyroidism (HPT), 8 patients with hypercalcaemia of other origin and 10 healthy control subjects. PTH and ionized calcium concentrations were measured at 5–10 min intervals. In all three groups the infusion caused a linear decrease in plasma ionized calcium. In both the HPT patients and the healthy subjects there was a prompt increase in the serum levels of parathyroid hormone (PTH) until a plateau was reached. The PTH response of the HPT patients appeared already within the hypercalcaemic range and the plateau value was attained at higher levels of PTH and ionized calcium than in the healthy subjects. The enhanced response distinguished half of the HPT patients with basal PTH values within the reference range from the healthy controls. The patients with nonhyperparathyroid hypercalcaemia displayed no increase in PTH values until the ionized calcium concentration was reduced far into or below the reference range. Thus the EDTA infusion permitted a complete differentiation between HPT and other causes of hypercalcaemia. In most cases an infusion over 30 min was sufficient for this purpose.