title: Does a high concentration of calcium in the urine cause an important renal concentrating defect in human subjects?
abstract: The objective of this study was to evaluate the hypothesis that a high concentration of ionized calcium in the lumen of the medullary collecting duct causes an osmole-free water diuresis. The urine flow rate and osmolality were measured in normal human subjects, as well as in patients with a history of nephrolithiasis who excreted more than 5 mmol of calcium per 24 h. There was an inverse relationship between the concentration of calcium in the urine and the 24 h urine volume both in normal subjects and in patients with a history of nephrolithiasis. When the concentration of calcium in the urine was greater than 5 mmol/l, the urine volume was less than 1 litre per day in the majority of subjects. After 16 h of water deprivation, when the concentration of calcium in the urine was as high as 17 mmol/l (ionized calcium 7.4 mmol/l), urine osmolality was 1258 mOsm/kg of water and the urine flow rate was 0.30 ml/min. We conclude that, although a calcium receptor may be present in the lumen of the medullary collecting duct in human subjects, an extremely high concentration of urinary total and ionized calcium does not cause a clinically important defect in the renal concentrating process.
authors.affiliation: Renal Division, St. Michael's Hospital, University of Toronto, Toronto, Ontario M5B 1A6, Canada.
authors.forename: G S
authors.initials: GS
authors.lastname: Lam
authors.forename: J R
authors.initials: JR
authors.lastname: Asplin
authors.forename: M L
authors.initials: ML
authors.lastname: Halperin
mesh_terms: D000293:Adolescent; D000328:Adult; D002118:Calcium / Q000652:urine*; D016022:Case-Control Studies; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D007669:Kidney Calculi / Q000503:physiopathology* / Q000652:urine; D007671:Kidney Concentrating Ability; D008875:Middle Aged; D009994:Osmolar Concentration; D014556:Urine; D014868:Water Deprivation / Q000502:physiology
chemical_list: D002118:Calcium