Glomerular Filtration Rate in Sick Neonates: A Focus on Cystatin C

The use of creatinine as an endogenous marker of estimated glomerular filtration rate (eGFR) is well-established in clinical practice, despite its limitations. As a step toward limiting this drawback, cystatin C and various biomarkers came into use in determining renal function. In sick neonates, various pathologies may impair renal function thus, underscoring the need for accurate estimation of glomerular filtration rate (GFR). This study aimed at evaluating the use of cystatin C in estimating the GFR of sick neonates in comparison to creatinine. A hospital-based descriptive study was conducted at a tertiary center in North Central, Nigeria, for 4 months. One hundred and seventy-three sick neonates admitted into the special care baby unit were recruited. Blood was sampled at admission for determination of serum creatinine and cystatin C levels, while a repeat sample for creatinine was taken 48 hours after. GFR was estimated using the Schwartz formula for creatinine and the Zappitelli equation for cystatin C and compared with an inulin reference. The median (interquartile range [IQR]) eGFR derived from cystatin C was 48.8 (21.0) mL/min/1.73 m2, it was higher than the median creatinine-derived GFR at admission and was of statistical significance. It is also approximated closer to the inulin reference. The median (IQR) eGFR derived from creatinine at admission was 21.2 (21.4) mL/min/1.73 m2. Creatinine-derived eGFR was significantly lower in babies with asphyxia and neonatal sepsis compared to those who did not have these diagnoses. Cystatin C-derived eGFR showed no variation between the various diagnoses. In conclusion, cystatin C is a useful and unbiased determinant of eGFR in sick neonates as compared to creatinine.