The discovery that serum phenylalanine is increased in the metabolic disease phenylpyruvic oligophrenia has made desirable the availability of a relatively simple and accurate method for its determination in serum. This has become even more important since the observations that urine phenylpyruvic acid, which has been the commonly used test for this disease, may not be detected until the serum levels of phenylalanine exceed about 15 mg. per 100 cc.1 and that infants less than one month old with this disease may not show the presence of phenylpyruvic acid in the urine, whereas the serum phenylalanine is elevated within five days.2
Microbiological methods 3 have been used, but these do not meet the requirement of simplicity. Udenfriend and Cooper4 have proposed a chemical method in which the phenylalanine is enzymatically decarboxylated to phenylethylamine by use of an extract of Streptococcus faecalis and then the phenylethylamine is quantitated
HENRY RJ, SOBEL C, CHIAMORI N. Method for Determination of Serum Phenylalanine with Use of the Kapeller-Adler Reaction. AMA Am J Dis Child. 1957;94(6):604–608. doi:10.1001/archpedi.1957.04030070016003
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