Determinants of renal function in preterm newborns

Background: Little is known about potential endogenous biomarkers of renal function other than serum creatinine (sCr). Aims: to evaluate cystatine C (CysC) and beta-trace protein (BTP) levels in preterm newborns and to assess the impact of kidney-detrimental factors on kidney function. Methods: newborns with GA<32 weeks (wks) were enrolled. Blood samples were obtained on the 3rd day of life (T0) and when they reached a GA of 36wks (T36), and sCr, CysC, BTP and urea levels were measured. eGFR was calculated according to 9 existing formulas at T36. Pre-natal and postnatal kidney injury risk scores were calculated by the number of potentially kidney-detrimental factors. Results: We collected data from 71 newborns at T0 (31 with GA 28 wks) and from 53 subjects at T36 (25 with GA 28wks). At T0, newborns with GA£28 weeks had higher sCr levels than those with GA>28wks (p=0.016). At T0, sCr was negatively correlated with GA (R= -0.315, p=0.009), whereas CysC and BTP were not influenced by GA. At T36, newborns with GA 28 wks had lower sCr, BTP and higher urea levels (p=0.007, p=0.005 and p=0.029, respectively). At T36 eGFR values calculated by the four formulas using only CysC were not different in newborns with GA 28 and >28wks. eGFR values estimated by other formulas were higher in subjects born at a lower GA. We found a direct correlation between the post-natal score and eGFR estimated according to the sCr-based formulas by Schwartz2009 (R=0.345, p=0.027) and Brion (R=0.312, p=0.044), not persisting after adjustment for urea levels at T36 and GA. No correlations were found between the scores and eGFR according to the other formulas. Conclusions: eGFR formulas using CysC are not influenced by GA. Post-natal score shows a direct correlation with eGFR according to sCr-based formulas, which does not persist after adjustment for GA and urea levels, showing that the underlying confounder may be the nutritional status of preterm newborns, as suggested by the higher urea levels in newborn with GA 28wks at T36.