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.