Circulating vitamin D metabolites and hypercalcaemia of malignancy

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Abstract
Plasma concentrations of 1,25 dihydroxycholecalciferol were measured in 44 patients with malignancy associated hypercalcemia and related to other hormonal regulators of Ca metabolism. Immunoreactivity parathyroid hormone [PTH] concentrations were suppressed in all but 2 patients and, as a group, patients with hypercalcemia of malignancy had lower 1,25 dihydroxycholecalciferol concentrations than normocalcemic cancer patients. 1,25 dihydroxycholecalciferol concentrations were clearly detectable in a significant proportion (43%) of hypercalcemia cases suggesting that in these patients the active vitamin D metabolite may contribute to the pathogenesis and maintenance of the hypercalcemia by stimulating bone resorption, and or by increasing absorption of Ca from the intestine. Measurement of plasma 1,25 dihydroxycholecalciferol concentration does not provide a wholly reliable method for distinguishing the hypercalcemia of malignancy from primary hyperparathyroidism.