A comparison of nephrogenous cyclic AMP, total urinary cyclic AMP and the renal tubular maximum reabsorptive capacity for phosphate in the diagnosis of primary hyperparathyroidism.

Abstract

SUMMARYA determination was made of total urinary adenosine 3′‐5′cyclic monophosphate (UcAMP), nephrogenous cyclic AMP (NcAMP) excretion and also of the renal tubular maximum reabsorptive capacity for phosphate TmPO4/GFR (all expressed as a function of the glomerular filtrate) in fourteen patients with primary hypercalcaemic hyperparathyroidism and twelve control normal subjects. The hyperparathyroid patients gave a mean excretion of UcAMP (7·0 ± 45·68 nmol/100 ml GF; mean ± SEM), NcAMP (6·19 ± 0·64 nmol/100 ml GF) which were significantly greater (P < 0·001) than those of normal controls, (2′45 ± 0·15nmol/100 ml GF and 1·25 ± 0·12nmol/100 ml GF) respectively. The difference between the patients and controls for the maximum renal tubular reabsorptive capacity for phosphate (TmPO4/GFR) (patients 0·55 ± 0·04, controls 1·05 ± 0·05 mmol/l GFR) was also highly significant (P<0·001). Statistical evaluation of the results obtained from the patients with primary hyperparathyroidism revealed that there was a positive correlation between the level of plasma calcium and immunoreactive parathyroid hormone (PTH) (r=+0·46), NcAMP(r=+0·337), UcAMP (r=+0·36), and an inverse correlation with the TmPO4/GFR (r=−0·62). There was also a positive correlation between plasma immunoreactive PTH and NcAMP(r=+0·31), and UcAMP(r=+0·35), and an inverse correlation with the TmPO4/GFR (r=−0–39). Successful removal of a single parathyroid adenoma in six patients was associated with a highly significant fall in the excretion of UcAMP, NcAMP, and a rise in the TmPO4/GFR (P<0·005). The combination of a low TmPO4/GFR and a high excretion of UcAMP or NcAMP in the presence of hypercalcaemia is highly suggestive of primary hyperparathyroidism in the absence of clinical evidence of malignant disease.