Is serum cystatin C a better marker of kidney function than serum creatinine in septic newborns?

Introduction: Several studies have claimed that the estimation of serum cystatin C could be a better marker of kidney excretory function than serum creatinine. However, its role in the diagnosis of reduced kidney function was not unquestionably confirmed. The aim of this study was to analyze the concentrations of serum cystatin C in neonates with sepsis. Material/Methods: Thirty-two neonates (gestational age from 34 to 40 weeks) admitted to the NICU during the first 14 days of life were enrolled. Serum cystatin C concentrations were estimated by ELISA during three successive days in neonates treated for infection. The study group consisted of 9 newborns with sepsis, 14 with severe sepsis and 9 with septic shock. Results/Discussion: At the beginning of the observational period the mean serum concentration of cystatin C in the study group was 1.35 mg/L (95% CI 1.20-1.49). Surprisingly, the lowest concentration of cystatin was observed in patients with septic shock (1.23 mg/L; 95% CI 0.92-1.54) within the observation period. Higher concentrations were found in neonates with sepsis (1.47 mg/L; 95% CI 1.04-1.90) and severe sepsis (1.50; 1.12-1.87). There was no correlation between serum cystatin C concentration and serum creatinine or gestational age. A significant cor relation was discovered between chronological age and cystatin C (R=-0.439, p=0.01). There was a tendency for cystatin C to decline during the second observational day in patients with sepsis (to 1.53 mg/L; 95% CI: 1.19-1.86) and severe sepsis (to 1.32 mg/L; 95% CI: 1.07-1.57), while a slight insignificant increase in patient with septic shock (to 1.28 mg/L; 95% CI: 0.88-1.68) was revealed. The interrelation between age and cystatin C concentration disappeared in the following days of stay in the NICU. Even in patients who died in the course of septic shock the observed changes in cystatin C levels were small and did not exceed those of serum creatinine. Conclusions: Cystatin C is not a useful marker of kidney function in neonates with sepsis.