Creatinine and Cystatin-C Levels in Late Preterm and Small-for-Gestational-Age Neonates – An Observational Study

Objectives: Cystatin-C, produced by all nucleated cells, remains unaffected by muscle mass, hence maybe a better renal function marker than creatinine. We compared cystatin-C levels in healthy term appropriate-forgestational-age (AGA), term small-for-gestational-age (SGA), and late-preterm AGA neonates. Material and Methods: This observational study was conducted from June to October’2023. After informed consent, term-SGA ( n = 55), late-preterm ( n = 55), and term-AGA neonates ( n = 110) were enrolled. Neonates with anomalies, asphyxia, and requiring neonatal intensive care unit admission were excluded. Maternal, cord, and day 3 blood samples were collected and stored at −80℃. Cystatin-C was estimated by the Automated Immunoturbidimetry method and creatinine by Jaffe’s method. After correlation, regression analysis was performed for determinants of day 3 creatinine and cystatin-C, and a percentile table was generated. Results: Median (interquartile range) of gestation and birthweight among term AGA, term-SGA, and late-preterm AGA neonates were 38.4 (38.1–39.3), 38.5 (38.1–39.5), and 36.1 (35.4–36.4) weeks; 3.085 (2.840–3.465), 2.340 (2.160–2.420), and 2.320 (2.150–2.480) kg, respectively. Maternal and cord creatinine had a strong correlation (r = 0.832, P < 0.001). Day 3 creatinine was lower in term-SGA than term-AGA neonates (0.61 ± 0.19 vs. 0.67 ± 14, P = 0.042). No correlation observed between maternal and cord cystatin-C. Cystatin-C on cord and day 3 was higher in late-preterm neonates than term AGA; 1.708 ± 0.34 versus 1.549 ± 0.44; P = 0.011 and 1.528 ± 0.32 versus 1.426 ± 0.43 mg/L; P = 0.012, respectively. Regression analysis showed cord cystatin-C predicted day 3 cystatin-C (R 2 = 0.963, P < 0.001). Cystatin-C 95 th centile on day 3 in term-AGA, term-SGA, and late-preterm AGA neonates was 2.193, 2.090, and 2,198 mg/L. Conclusion: Serum cystatin-C on day 3 is independent of maternal influence and values are higher in late preterm neonates. The cystatin-C percentile chart may guide subsequent research in sick neonates.