title: Urinary Vitamin D-Binding Protein as a Biomarker of Steroid-Resistant Nephrotic Syndrome.
abstract: BACKGROUND
  Idiopathic nephrotic syndrome (NS) is one of the most common glomerular disorders of childhood and is associated with increased urinary vitamin D-binding protein (uVDBP) excretion. We tested the hypothesis that uVDBP represents a biomarker to differentiate steroid-resistant nephrotic syndrome (SRNS) from the more benign forms of steroid-sensitive nephrotic syndrome (SSNS).
  
  
  METHODS
  This cross-sectional study included children with SRNS (n = 24), SSNS (n = 28), and normal controls (n = 5). Urine and clinical data were collected from patients. Measurements of uVDBP were performed with a commercially available ELISA kit and normalized to urine creatinine.
  
  
  RESULTS
  Concentrations of uVDBP were significantly higher (P < 0.001) in patients with SRNS (13,659 ng/mL, interquartile range [IQR] 477-22,979) than in patients with SSNS (94 ng/mL, IQR 53-202) and normal controls (23 ng/mL, IQR 22-99, P = 0.002). Significance did not change when the results were corrected for urine creatinine. uVDBP was significantly negatively correlated with estimated glomerular filtration rate (eGFR; R = -0.76, P = 0.03). However, uVDBP was still markedly elevated in patients with SRNS with eGFR >100 mL/minute/1.73 m(2). There was a positive correlation between microalbuminuria (MALB/Cr) and uVDBP (R = 0.67, P < 0.001). However, uVDBP displayed a much higher discriminatory ability for distinguishing SRNS than MALB/Cr (area under the curve = 0.92 vs 0.67, respectively). An uVDBP cutoff of 362 ng/mL yielded the optimal sensitivity (80%) and specificity (83%) to distinguish SRNS from SSNS.
  
  
  CONCLUSIONS
  In this preliminary study, uVDBP represents a noninvasive biomarker that could distinguish SRNS from the more benign SSNS with high discriminatory power.
authors.affiliation: Assistant Professor, Division of Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Bennett
authors.affiliation: Summer Student, Division of Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
authors.forename: Angad
authors.initials: A
authors.lastname: Pordal
authors.affiliation: Research Assistant, Division of Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Haffner
authors.affiliation: Clinical Fellow, Division of Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
authors.forename: LaTawnya
authors.initials: L
authors.lastname: Pleasant
authors.affiliation: Research Assistant, Division of Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
authors.forename: Qing
authors.initials: Q
authors.lastname: Ma
authors.affiliation: Professor, Division of Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
authors.forename: Prasad
authors.initials: P
authors.lastname: Devarajan
keywords: biomarkers; focal segmental glomerulosclerosis; minimal change disease; nephrotic syndrome; steroid resistance; vitamin D