Is serum CRP level a reliable inflammatory marker in pediatric nephrotic syndrome?

Background: This study tested the hypothesis that during massive proteinuria, C-reactive protein (CRP) may be lost into the urine along with other proteins, making serum CRP (sCRP) level an unreliable marker of infection severity in nephrotic syndrome (NS). Methods: Children with active NS (n = 23) were compared with two matched control groups: patients with febrile non-renal infectious disease (n = 30) and healthy subjects (n = 16). Laboratory measurements included sCRP, urine protein, creatinine, IgG, and protein electrophoresis. Urinary CRP (uCRP) was measured by ELISA. Results: Sixty-nine patients were enrolled: 23 patients with NS, 30 patients with non-renal febrile infectious diseases, and 16 healthy children. Median uCRP concentrations were 0 mcg/gCr (0–189.7) in NS, 11 mcg/gCr (0–286) in the febrile group, and 0 mcg/gCr (0–1.8) in the healthy group. The uCRP/creatinine ratio was similar in the NS and healthy groups (p > 0.1) and significantly higher in the febrile group than the other two groups (p < 0.0001). There was no association of uCRP concentration with severity of proteinuria or IgG excretion. Conclusions: NS in children is not characterized by significant loss of CRP into the urine. Therefore, sCRP may serve as a reliable marker of inflammation in this setting. The significant urinary excretion of CRP in children with transient non-renal infectious disease might be attributable to CRP synthesis in renal epithelial cells.