Urinary Sodium Doesn’t Predict Kidney Failure Risk

For patients with nondiabetic chronic kidney disease (CKD), urinary sodium excretion rate is not associated with the long-term risk of kidney failure, reports a study in Kidney International.

The study used data from 840 patients, mean age 51.7 years, enrolled in the Modification of Diet and Renal Disease Study. Only 5 percent had a history of diabetes. Baseline 24-hour urinary sodium excretion was analyzed for association with the long-term risk of kidney failure and with a composite outcome of kidney failure or all-cause mortality. Exploratory analyses evaluated the possible effects of GFR, proteinuria, and angiotensin-converting enzyme inhibitor use on the relationship between urine sodium and kidney failure.

At a median 6 years’ follow-up, 617 patients had experienced kidney failure, and 723 had met the composite outcome. The mean baseline 24-hour urinary sodium excretion was 3.46 g/day, with quartile means of 2.14, 2.05, 3.70, and 4.96 g/day. However, the primary analysis found no significant association between urine sodium level and either outcome. This was so when both the initial baseline 24-hour urinary sodium level and the cumulative mean time-dependent values were used.

Exploratory analysis suggested a significant interaction with baseline proteinuria. In a two-slope model, at urine sodium excretion of less than 3g/day, higher urine sodium levels were associated with increased risk of kidney failure in individuals with baseline proteinuria less than 1g/day. By contrast, individuals with baseline proteinuria of 1 g/day or higher were at lower risk of kidney failure. There was no interaction among individuals with urine sodium of 3 g/day or higher.

The current guidelines recommend sodium intake of less than 2 g/day for patients with CKD; yet there are few data showing that sodium intake affects long-term outcomes. The new study shows no difference in kidney failure risk by urinary sodium excretion level in a population of patients with mainly nondiabetic CKD. Further study is needed to confirm the possible interaction with proteinuria [Fan L, et al. Urinary sodium excretion and kidney failure in nondiabetic chronic kidney disease. Kidney Int 2014; 86:582–586].