Clinical Application of Tetrahydrobiopterin Loading Test in Differential Diagnosis of Hyperphenylalaninemia

Objective To explore the application value of tetrahydrobiopterin(BH4) loading test in differential diagnosis of hyperphenylalaninemia(HPA).Methods From January,2008 to June,2010,BH4(20 mg/kg) loading test was carried out in 27 patients with HPA,and phenylalanine(Phe,100 mg/kg) combined with BH4 loading test were performed in the patients whose basic phenylalanine blood concentrations were less than 6 mg/dl.The urinary pterine profile analysis and dihydropteridine reductase(DHPR) activity in dry blood filter spot were analyzed simultaneously.Results The characteristic curves of the blood levels were observed in 27 patients after BH4 loading test.Among them,5 patients were diagnosed as BH4 deficiency,9 patients as BH4 responsive PAH deficiency.9 of 22 moderate PKU patients were diagnosed as BH4 responsive PAH deficiency.Conclusions BH4 loading test plays an important role in early differential diagnosis of HPA patients.Some patients with moderate PKU are responsive to BH4 and can be treated with BH4.