Quantitation of total biopterin and tetrahydrobiopterin in plasma.

OBJECTIVE: To develop a reliable method for the determination of tetrahydrobiopterin and total biopterin in plasma. METHODS: Modifications include blood collection and handling procedures. RESULTS: Collection of blood in the presence of 0.1% (w/v) dithiothreitol and waiting for 2-3 h before centrifugation are optimal for adequate quantitation of both pterins. CONCLUSIONS: For a reliable determination of tetrahydrobiopterin and total biopterin in plasma, blood tubes must contain a dimercapto-antioxidant and time between blood collection and centrifugation is critical.