Urinary sodium excretion and kidney failure in non-diabetic chronic kidney disease

Current guidelines recommend under 2g/day sodium intake in chronic kidney disease, but there are few studies relating sodium intake to long-term outcomes. Here we evaluated the association of mean baseline 24-hour urinary sodium excretion with kidney failure and a composite outcome of kidney failure or all-cause mortality using Cox regression in 840 participants enrolled in the Modification of Diet in Renal Disease Study. Mean 24-hour urinary sodium excretion was 3.46 g/day. Kidney failure developed in 617 and the composite outcome was reached in 723. In the primary analyses there was no association between 24-hour urine sodium and kidney failure [HR 0.99 (95% CI 0.91–1.08)] nor on the composite outcome [HR 1.01 (95% CI 0.93–1.09),] each per 1g/day higher urine sodium. In exploratory analyses there was a significant interaction of baseline proteinuria and sodium excretion with kidney failure. Using a 2-slope model, when urine sodium was under 3g/day, higher urine sodium was associated with increased risk of kidney failure in those with baseline proteinuria under 1g/day, and lower risk of kidney failure in those with baseline proteinuria of 1g/day or more. There was no association between urine sodium and kidney failure when urine sodium was 3g/day or more. Results were consistent using first baseline and time-dependent urine sodium. Thus, we noted no association of urine sodium with kidney failure. Results of the exploratory analyses need to be verified in additional studies and the mechanism explored.