OBJECTIVES: Regular and accurate monitoring of blood @entity815 ( @entity815 ) and @entity669 (Tyr) levels is prerequisite for a successful management of @entity1 with @entity814 ( @entity814 ). We aimed to compare the tandem mass spectrometry ( @entity15 / @entity15 ) and the @entity535 analyzer (AAA) as methods to measure blood @entity815 and Tyr levels and @entity815 /Tyr ratio. METHODS: Venous blood samples were collected for the AAA analysis, using Pinnacle PCX (Pickering Laboratories), with HPLC Series 1200 (Agilent). Capillary blood was spotted directly on filter paper (Whatman 903) for the @entity15 / @entity15 analysis, using 3200 QTrap AB SCIEX and Perkin Elmer Series 200 HPLC system. The Bland-Altman test was used to compare agreement between the methods and Pearson correlation coefficient to assess the association between the methods. RESULTS: 207 pairs of measurements were performed. The @entity815 levels (range 0-2500 M) obtained by the @entity15 / @entity15 were on average 26.1% (SD 13.9%) lower compared to those obtained by the AAA. The Tyr levels by the @entity15 / @entity15 were on average 15.5% (SD 20.6%) lower. The @entity815 /Tyr ratio by the @entity15 / @entity15 was on average 10.6% (SD 15.9%) lower. The Pearson correlation coefficients for @entity815 (range 0-2500 M), Tyr and the @entity815 /Tyr ratio were 0.984 (p<0.001), 0.841 (p<0.001) and 0.987 (p<0.001) respectively. CONCLUSIONS: When monitoring blood @entity815 and Tyr levels in @entity1 with @entity814 , clinicians need to be informed about the method used. Due to the considerable inter-assay variability, a single method is preferable for long-term follow-up of @entity1 . When using @entity15 / @entity15 , on average 26% lower blood @entity815 levels were obtained as compared to the AAA. The guidelines and recommendations on @entity814 management should take into consideration the differences in laboratory methods.

Comparison of tandem mass spectrometry and XXXX analyzer for @entity815 and @entity669 monitoring-Implications for clinical management of @entity1 with @entity814 .

@entity1 :: ('9606', 'Species') :: ['patients'] @entity535 :: ('CHEBI:33704', 'Chemical') :: ['amino acid'] @entity814 :: ('MESH:D010661', 'Disease') :: ['hyperphenylalaninemia', 'HPA'] @entity815 :: ('CHEBI:28044', 'Chemical') :: ['Phe', 'phenylalanine'] @entity669 :: ('CHEBI:18186', 'Chemical') :: ['tyrosine'] @entity15 :: ('MESH:D009103', 'Disease') :: ['MS']
@entity535 :: (CHEBI:33704,Chemical) :: ['amino acid']
