In 1934 Følling described phenylpyruvic oligophrenia and the characteristic color reaction of the urine with ferric chloride.1 Since then the disease has been related to a hereditary deficiency of the enzyme which converts phenylalanine to tyrosine, and lately it has been shown that the earlier in life a diet low in phenylalanine is instituted, the better the chances for ameliorating the convulsive, behavioral, and intellectual disturbances of this disorder.2 Hence the ferric chloride test, already widely used in the diagnostic evaluation of mental deficiency, has assumed practical importance. Recently the usefulness of a simple and reliable paper strip method (Phenistix reagent strips) of detecting phenylketonuria has been reported.3
The present note deals with the use of an improved form of Phenistix. The test material consists of a stiff strip of cellulose impregnated with ferric and magnesium ions and cyclohexylsulfamic acid. The ferric ions react with phenylpyruvate to
Nellhaus G. CLINICAL USE OF PHENISTIX REAGENT STRIP METHOD OF TESTING URINE SAMPLES. JAMA. 1959;170(9):1052–1053. doi:10.1001/jama.1959.63010090003010a
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