Absence of a significant renal threshold for two aromatic acids in phenylketonuric children over two years of age

There is a steady and nonlinear relationship between the levels of both phenylpyruvic acid (PPA) and o-hydroxyphenylacetic acid (oOPAA) in urine and the plasma levels of phenylalanine (phe) in children more than two years of age with phenylketonuria (PKU). If phe levels in blood rise above 0.35 mM (5.8 mg/100 ml) both aromatic acids are found regularly in urine. Typically, urinary concentrations of PPA are about 5 times higher than those of oOPAA. This report is based on the analysis of 94 samples from 51 children, on or off diet.