Cystatin C versus creatinine as a marker of glomerular filtration rate in the newborn
AIM: Serum cystatin C (cysC) has been proposed as a promising endogenous marker of glomerular filtration rate (GFR) in adults and children. The aim of this study was to determine the reference values of cysC at birth and three days later in comparison with creatinine (Cr) and Schwartz's estimated clearance. PATIENTS AND METHODS: 75 newborns (42 boys, 33 girls) were enrolled in the study. The gestational age ranged from 34 to 41 weeks, and the birth weight from 2070 to 4410 g. Blood samples were taken from the umbilical cord at birth and from a peripheral vein three days after birth. CysC and Cr were measured in all serum samples and values analyzed in different subgroups of neonates according to sex, gestational age, birth weight, umbilical blood pH, the influence of bilirubin, hemoglobin and hydration state. The Mann-Whitney U-test and Wilcoxon's analysis were used. RESULTS: At birth, serum cysC values ranged from 1.38 to 3.23 mg/l, not significantly decreasing after 3 days of life. Cr levels, determined simultaneously at birth, ranged from 34 to 99 μmol/l and were also not significantly different from day 3 levels. Both CysC and Cr levels were independent of sex, gestational age, birth weight, bilirubin levels and hydration state. CysC correlated positively only with the hemoglobin level (r = 0.28, P = 0.01) and negatively with cord blood pH (r = −0.40, P = 0.001), similarly to Cr. Significant correlation was found between cysC and Cr in umbilical cord blood (r = 0.30, P = 0.006) and day 3 blood samples (r = 0.37, P = 0.001). No correlation was found between 1/cysC and Schwartz GFR in cord blood (r = 0.18, P = 0.18), but correlation became significant in day 3 blood samples (r = 0.27, P = 0.02). CONCLUSION: This study suggests that cysC is not more sensitive than Cr as a marker of GFR in the newborn.