• Journal of The Korean Society of Inherited Metabolic disease
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• v.16 no.2
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• pp.86-92
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• 2016

Purpose: The $BH_4$ loading test is an important test that distinguishes PKU from $BH_4$ deficiency and identifies the $BH_4$ reactivity of PKU patients. Phenylalanine and $BH_4$ loading tests are useful methods that can shorten the length of hospital stay while improving patients' convenience. However, sufficient research on the dose of phenylalanine loading and $BH_4$ administration time after the loading has not been carried out. The present study investigates the effectiveness of the existing phenylalanine loading method by analyzing the medical records of six patients who underwent the $BH_4$ loading test after taking 100 mg/kg of phenylalanine patients. Methods: The medical records of six patients who underwent the $BH_4$ load test after taking 100 mg/kg of phenylalanine were examined out of 207 patients who were followed up in the Genetic Metabolic Clinic in Soonchunhyang University Hospital. All of the six patients had a low phenylalanine diet. First, they were taking 100 mg/kg of phenylalanine. 3 hours later, 20 mg/kg of $BH_4$ were loaded. The phenylalanine levels in the blood were continuously measured at 1, 2, 4, 6, 8, 12, and 24 hours by setting the time the $BH_4$ was loaded as the basal. Results: The average of the highest phenylalanine concentrations of six patients was $20.0{\pm}11.70mg/dL$. One reached the highest concentration seven hours after taking phenylalanine; another reached it five hours after that, and the remaining three reached it four hours after that. Only one patient reached the highest concentration within three hours. The phenylalanine levels of four out of six patients (66%) rose above $400{\mu}mol/L$ after being loaded with phenylalanine. The phenylalanine levels of the remaining two were 6.1 mg/dL ($366{\mu}mol/L$) and 5 mg/dL ($300{\mu}mol/L$), respectively. Conclusion: One of six patients (16%) reached the highest concentration three hours after taking 100 mg/kg of phenylalanine and four patients (66%) reached $400{\mu}mol/L$ or higher phenylalanine levels. There were patients whose phenylalanine levels did not rise above $400{\mu}mol/L$ using a commonly known test method; moreover, this method had the disadvantage of reaching the highest concentration after more than three hours. Therefore, it is considered that taking 200 mg/kg or more of phenylalanine and performing $BH_4$ loading four to six hours after taking phenylalanine are helpful in proper diagnosis.