[Evaluation of the urinary and plasma urea ratio and osmolarity in newborn infants and malnourished children with pathological and normal renal function].

Previous evaluation of diagnostic tests for acute renal failure in children demonstrated that osmolality urine/plasms (U/P) ratio below 1.3, urea ratio below 4.8 and a negative mannitol test (absence of a diurteic response within one hour after intravenous administration of 60 ml/m2 of 12.5% mannitol solution) may be considered as valuable factors in this diagnosis. However, the validity of those ratios were in doubt in selected populations such as newborns and in severe malnourished children in whom an impairment in concentrating urine capacity can be anticipated. With the purpose to test the validity of these parameters, a group of 53 newborns and 68 children with severe malnutrition were studied. They were admitted to the hospital with dehydration secondary to acute diarrhea presenting oliguria and hyperpnea and before any treatment was given, urine and blood samples were taken to determine urea and osmolality U/P ratios besides routine chemistries. Mannitol test was performed when urine could not be obtained and in some cases in whom U/P results deserved confirmation with the biological test. Seven of the 53 newborn patients developed acute renal failure with negative mannitol test and further clinical course of persistent oliguria. Urea and osmolality U/P ratios were 3.0 +/- 1.5 and 1.07 +/- 0.01 respectively, whereas the remaining 46 newborns had afterwards an uneventful recovery presenting U/P ratios of 12.4 +/- 8.5 for urea and 1.32 +/- 0.57 for osmolality. The difference between the average values of urea U/P ratio of the patients with acute renal failure and those with functional oliguria, were statistically significant at the level of p less than 0.01, but there was no significant difference between osmolality ratio values.