Urinary cAMP and Calcium Excretion in the Fasting State and Their Response to Oral Calcium Loading in patients with Calcium Urolithiasis

Abstract

Patients (52) with idiopathic calcareous urolithiasis (ICU) were studied with an oral Ca loading test. Subjects (21) were normo-calciuric with no other detectable abnormalities (NDA). Of 31 patients with hypercalciuria, 16 had elevated fasting urinary Ca excretion (UCaE) (HFC) [high fasting Ca excretion] and 15 had normal UCaE (NFC) [noraml fasting Ca excretion]. The fasting UCaE was significantly higher and the theoretical renal threshold for phosphate (TmPO4) was significantly lower in ICU patients than in 19 control individuals. The mean post-oral Ca loading (Post Ca) UCaE rose significantly in hypercalciuric patients compared with control subjects; only 18/31 (58%) had values above the normal range. There was no correlation between the fasting UCaE and either the immunoreactive parathyroid hormone (iPTH) or nephrogenous cAMP (ncAMP) in ICU patients. The fasting ncAMP was normal in all subjects with ICU and 7 of 52 subjects had elevated fasting iPTH values. When ranked according to the fasting UCaE value, ICU patients formed a continuum in which the NDA and HFC groups represented the extremes. Apparently, the responses to oral Ca loading serve no useful role in the identification of an individual ICU patient either in terms of the pathogenetic subgroup or in the differentiation from normal controls.