The clinical utility of the tetrahydrobiopterin loading test in differential diagnosis among hyperphenylalaninemia patients

Objective: To emphasize early differential diagnosis in hyperphenyla-laninemia(HPA) patients by oral tetrahydrobiopterin(BH4) loading test.Methods: From May in 2005 to April in 2007,BH4(20mg/mg) loading tests were carried out in 51 patients with HPA,and a combined phenylalanine(Phe,100mg/kg) and BH4 loading tests were performed in the patients whose basic phenylalanine blood concentrations were less than 600μmol/L.The urinary pterins and dihydropteridine reductase activity in dried blood spots were measured simultaneously.Results:(1) The characteristic curves of the blood levels were observed in 51 patients after BH4 loading tests.Of the total,5 cases were diagnosed as BH4 deficiency,10 cases as BH4 responsive PAH deficiency.(2)9(52.9%) of 17 moderate PKU patients as BH4 responsive PAH deficiency.Conclusion: The BH4 loading test plays a importairt role in early differential diagnosis from patients with HPA.Some patients with moderate PKU are responsive to BH4 and be treated with BH4.