Assessment of renal function from plasma urea and plasma creatinine in children.

The diagnostic value of plasma urea and plasma creatinine, used separately and in combination, for assessment of renal function in children was determined from simultaneously measured values of plasma urea, plasma creatinine and glomerular filtration rate (GFR) in 357 children with different nephro-urological disorders. GFR was determined from the total [51Cr]EDTA plasma clearance measured by a reliable single injection method. Four levels of renal function (with the limits expressed as % of the age-dependent normal mean standard GFR) were defined: normal (greater than 75%); moderately decreased (75-52%); considerably decreased (51-28%); and severely decreased (less than 28%). Plasma concentrations of urea (mmol/l) and creatinine (expressed as a percentage of age-dependent normal mean value) were graded into low and high normal, moderately increased, considerably increased and severely increased values. Only by using plasma urea and plasma creatinine in combination all four levels of renal function could be predicted in the individual child with a high degree of certainty (probability 0.94-1.00). The results of the study indicate that the plasma concentration of urea and creatinine should be measured simultaneously, the results being used in combination with due consideration to the variability of plasma creatinine with age. By this procedure the majority of children, i.e. approximately 80%, with nephro-urological disorders who are referred to a paediatric clinic can have their level of renal function predicted with a high degree of certainty. Using plasma urea and plasma creatinine separately the corresponding figure is 50 and 60%, respectively.