Urinary cyclic AMP corrected for glomerular filtration rate in the differential diagnosis of hypercalcemia

To evaluate the usefulness of urinary cyclic AMP (U-cAMP) expressed as nmol/100 ml glomerulus filtrate (GF) when discriminating various hypercalcemic states, we studied 99 patients. Patients with primary hyperparathyroidism (PHPT) showed a positive correlation between individual S-calcium levels and U-cAMP, nmol/100 ml GF (females r=0.49, n=40, p less than 0.01 and males r=0.91, n=7 p less than 0.001). There was also a correlation between U-cAMP, nmol/100 ml GF, and the weight of the adenomas (females r=0.36, n=32, p less than 0.05) and males r=0.79, n=6, p less than 0.05). Patients with PHPT and normal renal function excreted more U-cAMP than controls, 6.0 +/- 1.6 versus 4.3 +/- 1.0 nmol/100 ml GF (mean +/- SD). Of 47 patients with PHPT and normal renal function, 29 showed values below the upper normal limit, 6.3 nmol/100 ml GF (mean +/-2 SD), of the control group; the overlap was 62%. When U-cAMP was expressed as mumol/24 hours, the overlap was 40/47 (85%) and, when expressed as mumol/g creatinine, 31/47 (66%). Three patients with sarcoidosis and two with malignancies and hypercalcemia showed excretory values of U-cAMP, nmol/100 ml GF, above the upper normal limit. Patients with acromegaly or prolactinoma showed normal values of U-cAMP, nmol/100 ml GF. The present data indicate that all three types of determinations of urinary cAMP based on 24 hour urine collections are of little value in the differential diagnosis of hypercalcemic states.