Importance of season and clearance correction in the definition of hypercalciuria. Preliminary report.

The urinary excretion of calcium derives from the complex interplay of the factors influencing the filtered load and the tubular handling of this ion. Obviously, in order to define hypercalciuria, the dietary intake of calcium has to be controlled (5) and the inter- and intraindividual variations in the clearance of creatinine must be corrected (4, 6, 9, 10, 11). As a matter of fact, without this correction hypercalciuria may even be undetectable in idiopathic renal stone-formers studied on a free diet (1). But one must also consider the possibility of additional variables. The recent observation of rather marked seasonal variations in the plasma level of the intermediary vitamin D3 metabolite, 25-hydroxy-cholecalciferol (25-OHCC), (2, 8) suggests that part of the normal variability in the renal excretion of calcium may be season-related. To elucidate this problem we undertook the present pilot study of the seasonal variations in the clearance-corrected renal calcium excretion of healthy volunteers taking a standard diet.