Measurement of phenylalanine in blood on filter paper as a method of monitoring PKU treatment

OBJECTIVES: Phenylketonuria (PKU) is a genetic disease with autosomal recessive inheritance. In Poland the microbiological Guthrie test for this disease was replaced by an enzymatic colorimetric test. The question is whether the colorimetric test might be used in monitoring treatment of PKU. SETTING: In 80 patients with PKU on routine treatment monitoring of serum phenylalanine concentrations (SPh) was compared with phenylalanine concentrations in blood on filter paper (PhBFP). METHODS: Measurements of SPh were by a fluorimetric method (McCaman and Robins), and those of PhBFP were by an enzymatic colorimetric method. RESULTS: The regression analysis of SPh compared with PhBFP gave the equation y=0.9219x+0.2389; for the reversed ratio: it gave y=1.0220x+0.55083. The correlation was 0.97 at p