Urinary vitamin D binding protein levels in children with idiopathic nephrotic syndrome: a biomarker differentiating steroid sensitive from steroid resistant nephrotic syndrome.

introductionThe primary objective of this study was to assess urinary vitamin D binding protein (uVDBP) levels in idiopathic nephrotic syndrome. Secondary objectives were to evaluate the ability of uVDBP to differentiate between steroid resistant nephrotic syndrome (SRNS) and steroid sensitive nephrotic syndrome (SSNS), and between minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) of SRNS.

methodsSixty-three cases of idiopathic nephrotic syndrome were included; 23 were first episode nephrotic syndrome (FENS), 24 were relapsing nephrotic syndrome (RNS), and 16 were steroid resistant. Eleven subjects were used as controls and 17 cases were under remission. ELISA kit was used to assay uVDBP.

resultsMedian uVDBP levels were increased across FENS, RNS, SRNS groups as compared to controls (P < 0.001). Median uVDBP was significantly higher in SRNS (32.2 ng/mL) than in SSNS (4.0 ng/mL, P < 0.001). Similarly, the median level was also significantly higher in FSGS (56.6 ng/mL) than in MCD (20.8 ng/mL, P = 0.005). The uVDBP was significantly lower during remission (1.2 ng/mL) than in the active (5.1 ng/mL) phase of the disease (P < 0.001). At the 12-ng/mL cut-off value, uVDBP had higher sensitivity, specificity, and area under the curve (100%, 97.9% and 0.983, respectively) for distinguishing steroid-resistant from steroid-sensitive patients. Significant positive correlation was found between uVDBP and urine protein/creatinine ratio (r = 0.441, P < 0.001) and negative correlation between uVDBP and serum albumin (r = -0.303, P = 0.019).

conclusionuVDBP level is related to disease activity and can distinguish not only steroid-resistant from steroid-sensitive, but also FSGS from MCD histological subtypes of steroid-resistant NS.