Cria O Gregory1, Chunli Yu, Rani H Singh. 1. Nutrition and Health Sciences Program, Graduate Division of Biological and Biomedical Sciences, Emory University, Atlanta, Georgia, USA.
Abstract
PURPOSE: Blood phenylalanine monitoring is critical for the management of phenylketonuria. We compared three methods for measuring blood phenylalanine concentration: the amino acid analyzer, high-performance liquid chromatography with fluorometric detection, and tandem mass spectrometry. METHODS: We studied 22 female patients with phenylketonuria, ages 12-48 years, who attended our Metabolic Camp. Blood was collected into heparinized tubes (for analysis by the amino acid analyzer) or filter paper (for analysis by high-performance liquid chromatography with fluorometric detection and tandem mass spectrometry). RESULTS: Blood phenylalanine concentrations of plasma measured by the amino acid analyzer were significantly higher than those obtained from whole blood on filter paper by high-performance liquid chromatography (difference: 102 microM; 95% confidence interval: 23, 181) and tandem mass spectrometry (difference: 137 microM; 95% confidence interval: 58, 216). Phenylalanine concentrations from high-performance liquid chromatography and tandem mass spectrometry were not significantly different (P = 0.5). CONCLUSIONS: When monitoring blood phenylalanine concentrations for dietary compliance, clinicians should be mindful of the method being used; analyses of whole blood on filter paper were consistently approximately 15% lower than analyses of plasma.
PURPOSE: Blood phenylalanine monitoring is critical for the management of phenylketonuria. We compared three methods for measuring blood phenylalanine concentration: the amino acid analyzer, high-performance liquid chromatography with fluorometric detection, and tandem mass spectrometry. METHODS: We studied 22 female patients with phenylketonuria, ages 12-48 years, who attended our Metabolic Camp. Blood was collected into heparinized tubes (for analysis by the amino acid analyzer) or filter paper (for analysis by high-performance liquid chromatography with fluorometric detection and tandem mass spectrometry). RESULTS: Blood phenylalanine concentrations of plasma measured by the amino acid analyzer were significantly higher than those obtained from whole blood on filter paper by high-performance liquid chromatography (difference: 102 microM; 95% confidence interval: 23, 181) and tandem mass spectrometry (difference: 137 microM; 95% confidence interval: 58, 216). Phenylalanine concentrations from high-performance liquid chromatography and tandem mass spectrometry were not significantly different (P = 0.5). CONCLUSIONS: When monitoring blood phenylalanine concentrations for dietary compliance, clinicians should be mindful of the method being used; analyses of whole blood on filter paper were consistently approximately 15% lower than analyses of plasma.
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