Influence of Postconceptional Age on the Renal Biomarkers in Very-Low-Birth-Weight Infants

Purpose: We investigated whether consecutive levels of new emerging renal bio­ markers, including serum cystatin C (CysC) and urinary neutrophil gelatinase­asso­ ciated lipocalin (NGAL)/creatinine (Cr) ratio, were affected by postconceptional age in very­low­birth­weight (VLBW) infants. Methods: Repeatedly measured samples for each infant were divided into four groups according to postnatal age: at birth (stage I), 3 to 7 days postnatally (stage II), 8 to 28 days postnatally (stage III), and >28 days postnatally (stage IV). The association bet­ ween renal biomarkers and postconceptional age was assessed using Pearson’s cor­ relation coefficient, and the mean values of renal biomarkers in the four stages were compared using repeated­measures analysis of variance. Results: For samples measured at birth, serum CysC (r=–0.358, P=0.032) and urinary NGAL/Cr ratio (r=–0.522, P=0.001) were negatively correlated with gestational age, whereas serum Cr (r=0.148, P=0.390) was not. In addition, for all samples measured, serum CysC (r=–0.209, P=0.012), urinary NGAL/Cr ratio (r=–0.536, P<0.001), and serum Cr (r=–0.311, P<0.001) were negatively correlated with postconceptional age. Compared with the mean values of the postnatal age­specific stages, serum CysC showed no significant differences in any of the four stages. However, the urinary NGAL/Cr ratio in stage IV was significantly different from those in stages I to III. Conclusion: Although urinary NGAL/Cr ratio and serum CysC were negatively cor­ related with postconceptional age considering renal development, serum CysC showed no significant differences in any of the four postnatal age­specific stages. Urinary NGAL/Cr ratio at >28 days postnatally seems to be more affected by post­ conceptional age than serum CysC in VLBW infants.