Present Status of Different Mass Screening Procedures for Phenylketonuria: Medical Research Council Working Party on Phenylketonuria

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Abstract
The Phenistix screening test for phenylketonuria in newborn infants, when used routinely at the recommended age of 4 to 6 weeks, passes as normal a substantial proportion—perhaps between a quarter and a half—of children with the disease, who are then diagnosed only after brain damage has occurred. Screening procedures based on three other tests—namely, the paper chromatography test for o-hydroxyphenylacetic acid in urine, the Guthrie test for phenylalanine in blood, and a modification of the Guthrie test for phenylalanine in urine—have been compared with each other and with the Phenistix test in a special field inquiry. Each of the three tests is more efficient than the Phenistix test for the detection of phenylketonuria at an early age. A full appraisal indicates that the Guthrie test on blood would be the most satisfactory of the three tests to replace the Phenistix test as a screening procedure. Routine use of this would involve comprehensive arrangements for obtaining a single specimen of blood by heel-prick from every newborn infant at the age of 6 days or more, but preferably not later than 14 days, and for the rapid and economical processing of the specimens and skilled interpretation of the results at a few laboratory centres. These requirements have not proved difficult to meet in practice in the area where this procedure has been studied. A positive screening test result does not signify a firm diagnosis of phenylketonuria, but is an indication for fuller investigation, most suitably at one of a small number of centres specializing in the management of phenylketonuria and other inborn errors of metabolism.