Selli Muljanto^1,, Sudung O. Pardede², Partini P. Trihono²

Tubular lesion is frequently found in steroid-resistant nephrotic syndrome (SRNS) with massive proteinuria, which produces proximal tubular dysfunction. The presence of tubulointerstitial injury will assist the selection of therapy in nephrotic syndrome (NS) patients. Tubular injury can be diagnosed using tubular function test such as fractional excretion of magnesium (FE Mg) and urinary β2-microglobulin (β2M) in addition to kidney biopsy. The aim of this study was to compare the FE Mg and urinary β2M in children with SRNS and steroid-sensitive nephrotic syndrome (SSNS) in order to be able to detect the presence of tubular injury on SRNS. A cross-sectional study was conducted on children aged 2-15 years with SRNS and SSNS in remission. The urinary β2M and FE Mg were examined on 31 subjects of SRNS and SSNS in remission respectively. The urinary β2M was measured using competitive binding enzyme immunoassay. Serum and urinary magnesium and creatinine were measured using colorimetric and enzymatic colorimetry method respectively, afterwards FE Mg calculated with the formula: . The mean of FE Mg in SRNS (2.34 (SD 1.37) %) was significantly higher than the SSNS in remission (1.59 (SD 0.85) %; p = 0.0065), as well the median of urinary β2M level in SRNS (0.50 (0.30-11.80) µg/mL) was higher than the SSNS in remission (0.40 (0.30-0.50) µg/mL; p <0.001). The urinary β2M was increased significantly in SRNS compared to SSNS (26/31 subjects vs 16/31 subjects, respectively; p = 0.007). The increase of FE Mg in SRNS is significantly higher than in SSNS in remission with a cut off point of 1.64% (21/31 subjects vs 11/31 subjects, respectively; p = 0.022). The FE Mg and urinary β2M level are higher in SRNS than SSNS in remission that indicate tubular injury in SRNS.

fractional excretion of magnesium, steroid-resistant nephrotic syndrome, tubular injury, urinary β2-microglobulin