Urinary indices during relapse of childhood nephrotic syndrome

Sodium retention is the hallmark of idiopathic nephrotic syndrome (INS). Sodium retention could be secondary to activation of renin-angiotensin-aldosterone axis or due to an intrinsic activation of Na(+)K(+) ATPase in the cortical collecting duct. Urine potassium/urine potassium + urine sodium (UK(+)/UK(+) + UNa(+)) is a surrogate marker for aldosterone activity and can be useful in differentiating primary sodium retention from secondary sodium retention in children with INS. This was a cross-sectional study of children with INS, presenting to our center from June 2007 to June 2008. Children were categorized into those with steroid responsive and steroid nonresponsive nephrotic syndrome. One hundred and thirty-four children with nephrotic syndrome were analyzed. The FeNa(+) was significantly lower during relapse than in remission but no such difference was observed with UK(+)/UK(+) + UNa(+). The values of FeNa(+) and UK(+)/UK(+) + UNa(+) across various categories of nephrotic syndrome were similar. Correlating FeNa(+) and UK(+)/UK(+) + UNa(+) with cut-off of 0.5 and 60%, respectively, we found 50% of steroid responsive children and 36% of steroid nonresponders having a corresponding UK(+)/UK(+) + UNa(+) of <60% along with low FeNa(+) of <0.5%, favoring primary sodium retention. Urinary indices did not vary with the type of steroid response. In early relapse, the urinary indices revealed an overlap of both primary and secondary sodium retention in most stable edematous children with nephrotic syndrome.