Abstract
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<0.05. DISCUSSION: Concentrations of SPh accepted for children with PKU are not uniform. In the Cracow centre, the range of accepted SPh concentrations are 2–6 mg/dl for children and <12 mg/dl for older patients. The concentrations of PhBFP accepted are somewhat higher than SPh, range from 4 to 10 mg/dl, and are a good indicator of an appropriate diet. CONCLUSIONS: (1) The comparison indicated that colorimetric measurements of PhBFP are effective in monitoring therapeutic PKU management. Tests can be performed more often and are more comfortable both for the patients and their parents. (2) The comparative results indicated a concentration of PhBFP ranging from 4 to 10 mg/dl to be the accepted value for children treated for PKU.