β-trace protein may be a more suitable marker of neonatal renal function

To determine the relationship between maternal and neonatal cystatin C (CysC) and β-trace protein (BTP), markers of glomerular filtration rate (GFR) on day 1 of life.

Blood levels of CysC, BTP, and creatinine (Cr) were analyzed from 128 healthy term and preterm neonates admitted to the neonatal intensive care unit (NICU) (36% female) to determine the relationship between gestational age and maternal levels on day 1 of life.

Maternal Cr correlated positively and significantly with neonatal Cr (r = 0.677, p < 0.0001) and CysC (r = 0.246, p < 0.012) on day 1 of life. Maternal BTP did not correlate with neonatal BTP. Gestational age correlated positively and significantly with neonatal Cr (0.427, p < 0.0001), CysC (r = 0.321, p = 0.001); and with maternal Cr (r = 0.452, p < 0.0001), CysC (r = 0.613, p < 0.0001), and BTP (r = 0.442, p < 0.0001). No correlation was found between gestational age and neonatal BTP. Upon considering the following age groups; 24 - 32, 33 - 36, and ≥ 37 weeks, maternal Cr continued to correlate with neonatal Cr, across all age groups, while no correlation was found with BTP, and CysC correlations were no longer significant. Throughout, neonatal values for CysC and BTP were higher, suggesting that low neonatal GFR was the main determinant for the variance. There was no difference in the median neonatal BTP across all age groups.

Maternal Cr and CysC may both cross the placenta while BTP may not. Placental crossing of Cr seems to be independent of gestational age. The reasons for the different placental handling of BTP and CysC remain unknown.