Renal function in neonatal hyperbilirubinemia

Urinary N-acetyl-beta-D-glucosaminidase as an early marker for acute kidney injury in full-term newborns with neonatal hyperbilirubinemia

Purpose. To investigate renal function estimated by markers in full-term newborns with hyperbilirubinemia. Methods. A total of 332 full-term newborns with hyperbilirubinemia and 60 healthy full-term newborns were enrolled. Total serum bilirubin, serum creatinine (Cr), serum blood urea nitrogen (BUN), serum cystatin C (Cys-C), urinary beta-2-microglobulin (β₂MG) index, and urinary N-acetyl-beta-D-glucosaminidase (NAG) index were measured before and after treatment. All newborns were divided into three groups according to total serum bilirubin levels: group 1 (221-256), group 2 (256-342), and group 3 (>342). Results. The control group and group 1 did not differ significantly in regard to serum Cr, serum BUN, serum Cys-C, urinary β₂MG index, and urinary NAG index. Urinary NAG index in group 2 was significantly higher than that in control group (P < 0.001). Between control group and group 3, serum Cys-C, urinary β₂MG index, and urinary NAG index differed significantly. The significant positive correlation between total serum bilirubin and urinary NAG index was found in newborns when total serum bilirubin level was more than 272 μmol/L. Conclusions. High unconjugated bilirubin could result in acute kidney injury in full-term newborns. Urinary NAG might be the suitable marker for predicting acute kidney injury in full-term newborns with hyperbilirubinemia.

Renal glomerular and tubular function in neonates with perinatal problems

OBJECTIVE

To investigate perinatal risk factors that may be associated with impaired renal function during the first 2 weeks of life.

METHODS

The case notes of 150 neonates of gestational age (GA) 34-36 weeks and 494 of GA > 36 weeks were studied. Clinical risk factors were retrieved, along with indices of renal function: serum creatinine (SeCr), fractional excretion (FE) of sodium (FENa) and potassium (FEK), and the urinary calcium to creatinine ratio (UCa/UCr). Associations were identified by multiple and logistic regression analysis.

RESULTS

In infants with GA > 36 weeks, raised SeCr was related to perinatal stress, odds ratio (OR): 1.9, confidence interval (CI): 1.2-2.9, p < 0.05, and to duration of treatment with aminoglycosides (AGs) (t = 2.4, p < 0.01); FEK was associated with jaundice (t = -3.1, p < 0.01), and FENa with duration of AGs treatment (t = 2.6, p < 0.01). Full-term neonates with both hypoxic-ischemic encephalopathy (HIE) and AGs administration had an 80% increase in OR for impaired SeCr levels. In infants of GA 34-36 weeks, SeCr was related to perinatal stress (OR: 9, CI: 1.3-38, p < 0.05), FEK to jaundice (t = -2.1, p < 0.05), and FENa to duration of AGs administration (t = 2.2, p < 0.05) and antenatal steroid treatment (OR: 0.8, CI: 0.6-0.95, p < 0.05).

CONCLUSION

In neonates, renal impairment, being multifactorial in origin, may be caused by the additive effect of different perinatal factors. The strong negative relationship observed between jaundice and K excretion merits further investigation.

Urinary enzyme changes in newborns with unconjugated hyperbilirubinemia

Various changes in renal function caused by unconjugated hyperbilirubinemia in newborns have been suggested in previous reports. Disclosing an injury in renal tubulus epithelium is feasible by measurement of urinary enzymes. Thus, renal function tests and urinary enzymes in 25 terms newborns with unconjugated hyperbilirubinemia were evaluated before and after phototherapy. Ten healthy term newborns without hyperbilirubinemia formed the control group. Mean values of the variables obtained before and after phototherapy in the study group and in the controls were, respectively: urine osmolality (osm/kg H2O): 0.147 +/- 0.009, 0.174 +/- 0.011, and 0.153 +/- 0.018; endogenous creatinine clearance (mL/min per 1.73 m2): 45.7 +/- 2.15, 46.0 +/- 1.6 and 46.7 +/- 3.9; fractional excretion of sodium (%): 1.27 +/- 0.30, 0.79 +/- 0.19 and 1.24 +/- 0.07; tubular phosphorus reabsorption (%): 85.8 +/- 3.3, 87.8 +/- 2.8 and 86.6 +/- 1.7; urinary N-acetyl-beta-D glucosaminidase/creatinine (IU/mg): 0.617 +/- 0.226, 0.574 +/- 0.214 and 0.619 +/- 0.210; fractional excretion of alkaline phosphatase (%): 0.422 +/- 0.103, 1.001 +/- 0.374 and 0.596 +/- 0.201; fractional excretion of lactic dehydrogenase (LDH; %): 0.102 +/- 0.019, 0.121 +/- 0.023 and 0.119 +/- 0.041; fractional excretion of AST (%): 0.433 +/- 0.127, 0.530 +/- 0.113 and 0.502 +/- 0.074; fractional excretion of alanine aminotransferase (ALT; %) 0.856 +/- 0.413, 1.619 +/- 1.076 and 1.066 +/- 0.366. No significant difference was found between these values before and after phototherapy in the study group, or between the values before phototherapy in hyperbilirubinemic neonates and in the control group. In conclusion, unconjugated hyperbilirubinemia up to a serum level of 18.4 mg/dL in term neonates does not seem to result in injury of normal tubulus epithelium as shown by urinary enzyme levels.