Serum cystatin C during 30 postnatal days is dependent on the postconceptional age in neonates.

Background: Cystatin C (CysC) is a promising endogenous marker for renal function. However, the reference serum CysC level is not sufficiently studied in neonates. This study was conducted to investigate the reference level of serum CysC for neonates, including very low birth weight infants according to the postconceptional age (PCA).
Methods: Serum CysC levels were measured in 883 blood samples (246 neonates including 127 premature infants). Infants with symptoms or signs of acute kidney injury, systemic illness, congenital anomaly, or renal pathology were excluded. CysC levels were analyzed for association between subgroups dichotomized by postnatal age and PCA.
Results: Reference ranges of serum CysC were determined and a decreasing trend of CysC levels was observed as PCA increased, except for the first 3 postnatal days. CysC levels were negatively correlated with gestational age at birth, and PCA (P < 0.001), while positively correlated with postnatal age and serum creatinine (P < 0.001).
Conclusion: The reference level of serum CysC was determined according to postnatal age and PCA. As the reference CysC level was dependent on gestational age and PCA, consideration of these parameters is warranted when assessing CysC levels in neonates.