We have studied 2,030 children and adolescents between 3 and 18 years
of age (578 girls and 622 boys). We obtained reference values of creat
inine, urea and urea/creatinine serum ratio in all of them, and creati
nine clearance (Cl(cr)) in 1,200. We found an increase in serum creati
nine levels with age in both sexes, with an uncharging serum urea leve
l that results in a decrease of serum urea/creatinine ratio. The Cl(cr
) increase with age, but not with sex. We suggest the use of the formu
la: FG = K.L/Pcr to determinate renal function; it was derived from co
mparison with Cl(cr) in 10 h. urine collections.