Increased excretion of o-hydroxymandelic acid in phenylketonuria.

o-Hydroxymandelic acid has been found in large amounts in the urine of patients with phenylketonuria by gas chromatography mass spectrometry selected ion monitoring. Using deuterated o-hydroxymandelic acid as an internal standard, five patients were found to excrete 150-340 ng mg-1 creatinine. This may be compared with the excretion of 4-16 ng mg-1 creatine by normal subjects. Neither o-octopamine nor o-synephrine were found in urine under conditions by which 1 ng mg-1 creatinine would have been detected.