To understand the effect of different levels of hyperbilirubinemia on the kidneys of newborn rats.

Ninety-six 7-day-old newborn SD rats were selected and randomly divided into normal control group (group C, n=32, intraperitoneal injection of normal saline 0.5 ml), test group 1 (group T1, n=32, intraperitoneal injection of bilirubin solution 100 μg/g), and test group 2 (group T2, n=32, intraperitoneal injection of bilirubin solution 200 μg/g). Four time-points were set at 0, 8 h, 24 h, and 48 h, with 8 rats for each time point. The general conditions of the rats were recorded, and the total serum bilirubin (TSB), serum creatinine, serum cystatin C (Cys-C), serum neutrophil gelatinase-associated lipocalin (NGAL), urine NGAL, and urine kidney injury molecule 1 (KIM-1) were determined. The kidneys were removed to make pathological sections, and the pathological changes of the kidneys were observed under microscope.

In group T1 and group T2, the TSB levels of at 8 h, 24 h and 48 h were higher than those at 0 h (P<0.05), and peaked at 24 h in both groups. After 8 h, the urine levels of NGAL in groups T1 or T2 were higher than those of group C. After 24 h, the urine levels of NGAL in group T2 were higher than those of group T1 (P<0.05). After 8 h, the urine levels of KIM-1 in group T2 were higher than those of groups C or T1 (P<0.05). After 24 h, the serum levels of Cys-C in group T2 were higher than those of group T1 or group C (P<0.05). Only at 48 h in group T2 were there dilation and congestion in some renal interstitial blood vessels as well as mild edema in some renal tubules.

Hyperbilirubinemia may damage the renal tubular function of rats. The higher the TSB level was, the more severe the damage was. Urinary KIM-1 was not as sensitive as urine NGAL in reflecting the renal tubular damage of newborn rats. When the level of hyperbilirubinemia was high and lasted for more than 24 to 48 hours, rats glomerular filtration function injury happened with slight structural damage to the renal tubules. Serum NGAL and serum creatinine were not as sensitive as serum Cys-C in reflecting the changes of glomerular filtration function.