Evaluation of renal functions in asphyxiated newborns

Renal injury due to perinatal asphyxia has not been systematically evaluated. The available studies have used variable definitions, incomplete investigations and none had a control group. The aim of this study was to evaluate systematically the renal functions in severely asphyxiated newborns and to find if abnormal renal function tests can predict adverse outcome (death or neurologic abnormality at discharge). In a prospective case-control design, 25 inborn babies >= 34 weeks gestation having asphyxia (5 min Apgar <= 6 or needing resuscitation >= 5 min) were enrolled as 'cases'. Simultaneously 25 gestation and weight matched babies with no asphyxia were enrolled as 'controls'. Renal function tests, calculated renal indices using timed urine collections and excretion of beta(2)-microglobulin and N-acetyl-beta-D-glucosaminidase (NAG) were monitored in both the groups for first 4 days of life. Fourteen (56 per cent) asphyxiated babies had acute renal failure (ARF) as compared to 1 (4 per cent) control (p = 0.002). Blood urea and serum creatinine values were significantly higher in asphyxiated babies on day 4 but not on day 2. Renal failure index and FeNa were higher in asphyxiated babies on both day 2 and day 4, but creatinine clearance was not different. Urinary excretion of both beta(2)-microglobulin and NAG was higher in the asphyxiated babies on day 2 as well as day 4. Five minute Apgar <= 6 had the best sensitivity to predict renal failure. A combination of high serum creatinine and high blood urea had 100 per cent sensitivity and negative predictive value to predict adverse outcome while serum creatinine > 1.5 mg/dl alone had the best specificity and positive predictive value. The renal parameters were however poorer predictors of adverse outcome in comparison to clinical markers like 5 min Apgar <= 3 and HIE stage II/III. Both glomerular and tubular involvement was seen commonly in babies with birth asphyxia. Clinical markers of asphyxia were better predictors of adverse outcome than renal function tests.