Abstract
The influence of sodium intake on the renal handling of calcium and sodium was studied in 2 patients with non-parathyroid hypercalcaemia and salt-losing renal disease. the renal calcium excretion (range 88-549 mg/24h) varies proportionally with the sodium excretion (range: 40-340 mEq/24h, r=0.99). This reflects a corresponding relationship between tubular reabsorption of calcium, TRCa% (range 91.5-69.0%) and of sodium TRNa% (range 97.6-86.8% r=0.99), both expressed in per cent of their respective filtered loads. On dietetic sodium restriction, during which the sodium excretion falls to 47 and 40 mEq/24h, the TRCa% does not exceed 90-91.5%. This is in keeping with the non-parathyroid nature of the hypercalcaemia, the values being clearly lower than in patients with hyperparathyroidism and a corresponding reduction of the glomerular filtration rate.
These findings stress the importance of always paying regard to the simultaneous sodium excretion when determining the renal handling of calcium.