Fasting urine excretion of magnesium, calcium, and sodium in patients with renal calcium stones

Abstract

Urine excretion of magnesium (Mg), calcium (Ca) and sodium(Na) was studied in patients with renal Ca stones having normal kidney function (n= 60), and in matched controls (n= 60), on a free diet following an overnight fasting period. In some formers, Mg was lower than in normals, whereas Ca was unusually high resulting in a significantly higher molar Ca/Mg ratio (p less than 0.001). 2. In 3 out of 4 stone groups Na excretion was significantly elevated because of reduced tubular reabsorption. In normals, fractional Na excretion varied between 0.44 and 0.54% of endogenous creatinine clearance, whereas it exceeded 1% in the stone patients. Conversely, the molar ratio Na/Ca was equal in all groups. 3. Fasting urinary cyclic AMP was comparable in both populations supporting the assumption that in the majority of patients Ca- or Mg- wasting via urine may not be responsible for secondary hyperparathyroidism. In small selected groups, losses of divalent cations may act in concert, leading to stimulation of the parathyroid glands. 4. Correlations between minerals and Na reveal a close relationship between Na, Ca and Mg in terms of clearance and excretion rate in patients and controls. Fractional Na and Ca excretion are correlated in patients but not in normals. This suggests that in the absence of phosphaturia, factors other than extracellular volume expansion and/or hyperparathyroidism are operative in stone disease. 5. The origin of fasting natriuresis and relative hypercalciuria may be ascribed to a change, as yet not causally identified, in distal tubular Na reabsorption.

Circadian variations in the risk of urinary calcium oxalte stone formation

“…The relative stability of oxalate and citrate concentrations thus indicates the close correlation between their elimination and urinary output which is the result of a passive phenomenon of tubular reabsorption [3,5,7]. Conversely, marked circadian oscillations in urine calcium and magnesium levels are indicative of excretions which are less dependent upon diuresis, because these cations undergo a process of active distal tubular reabsorption [4,9].…”

Magnesium and Renal Stone Disease

“…In general, stone formers appear to have a magnesium excretion not different from that of healthy nonstone forming subjects (1 1,20,26, 32, 40,47,48,52,53). In some studies, however, stone formers were reported to have a low urinary magnesium excretion, either in comparison with controls not matched for age and sex (19, 29, 34), or in comparison with an adequate matched control group (44,50).…”

Quantitative Element Investigations in Urine, Serum, Kidney and Muscle Tissue of Calcium Oxalate Stone Patients

“…Most authors report high percentages in hypercalciuric calcium oxalate stone patients (30%), whereas others also cite lower percentages (7, 9, 12). An increase as well as a decrease in the sodium excretion of stone patients is reported in the literature (14,15). Whereas magnesium values In our hospital we have therefore determined quantitatively, besides urine and serum investiga tions, the concentrations of some important ele ments in kidney and muscle tissue.…”