Urinary and Nephrogenous Adenosine 3′,5′-Monophosphate in the Hypercalcemia of Malignancy*

Plasma cAMP concentration (PcAMP) and urinary cAMP excretion (UcAMP) were determined in 91 patients with hypercalcemia and malignancy, 15 patients with a malignancy and normal serum calcium concentrations, and 28 patients with primary hyperparathyroidism to assess its usefulness in the differential diagnosis of hypercalcemia. The patients with hypercalcemia and malignancy were subdivided into 2 groups: those with evidence of skeletal metastases and those without evidence of skeletal metastases (pseudohyperparathyroidism). In addition to cAMP determinations, serum immunoreactive parathyroid hormone (IPTH) and serum electrolytes were determined in all patients. PcAMP was elevated in both the cancer patients with hypercalcemia and those who were normocalcemic, but not in the patients with primary hyperparathyroidism. The mean UcAMP excretion was at least 2-fold elevated in all patient groups. Since nearly half of UcAMP is derived through the renal filtration of PcAMP, the nephrogenous component of cAMP excre...