Comparison of two branched-chain amino acids (BCAAs) measurement methods for monitoring the treatment in inborn errors of metabolism
2Department of Inborn Errors of Metabolism and Pediatrics, Institute of Mother and Child, Poland
Background:
Newborn screening of inborn errors of metabolism (IEM) improved detection of affected children. The treatment and dietary recommendations in IEM require rapid and frequent monitoring of branched-chain amino acids concentrations in patients. The possibility of blood collection at home on the filter paper and sending it to the laboratory, can be helpful in monitoring the treatment. The aim of our study was finding out whether tandem mass spectrometry method is compatible with standard HPLC (High-performance liquid chromatography) technique. It is particulary important in monitoring of maple sirup urine disease (MSUD) and other organic aciduries.
Methods:
Two analytical methods were compared: detection of BCAAs in plasma by HPLC using o-phthalaldehyde and 3-mercaptopropionic acid (OPA-3MPA) derivatization with fluorescent detector and detection of BCAAs in dried blood spots using tandem mass spectrometry (LC-MS-MS). The 83 blood samples were collected simultaneously on standard newborn screening filter paper and on a tube containing lithium heparin.
Results:
The following correlations were found between the methods: valine R²= 0.8765, leucine R²=0.9654, isoleucine R²=0.9120, and allo-isoleucine R²=0.9636. The compatibility between methods was also confirmed by the Bland-Altman charts. Average biases between HPLC and LC-MS-MS method were: valine= 6.2%, isoleucine=-8.0%, leucine=-2.7%, allo-isoleucine=-25.5%, respectively.
Conclusion:
The LC-MS-MS method for determining BCAAs in a dry spot of blood collected on the filter paper may be useful for monitoring the concentration of these amino acids in IEM patients. This method appears to be more sensitive for allo-isoleucine determination compared to standard HPLC method.
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