Comparison of two different methods for measurement of phenylalanine in dried blood spots

Phenylketonuria is an inherited metabolic disorder caused by a defect in th e hydroxylation of phenylalanine. Newborn screening is crucial for the diag nosis and treatment of this disease. A phenylalanine dehydrogenase-coupled enzymatic assay (Quantase) in microtiter plates for the screening of phenyl ketonuria was evaluated and compared with our routine method based on the m odified fluorometric McCaman method. The test exhibited a linear calibratio n curve with a good slope as well as sufficient imprecision (< 10%), recove ry (99.23 +/- 4.86%) and limit of detection (54.5 <mu>mol/l). One hundred a nd ninety dried blood spots were analysed by this enzymatic method and comp ared with McCaman's. Although Quantase (Teknovas, Bilbao, Spain) showed a p henylalanine mean level in dried blood spot 18.2 mu mol/l higher than that obtained with our routine method, the agreement between both techniques was considered acceptable.