Methionine is oxidized to methionine sulfoxide during prolonged storage of samples. Loss of methionine can be corrected for by calculated total methionine, which is the sum of remaining methionine plus methionine sulfoxide (2).
Patient/subject: Prandial status affects concentration, which increases after a protein rich meal.
Matrix: Serum or EDTA plasma.
Volume: Minimum volume is 50 µL, but 200 µL is optimal and allows reanalysis.
Preparation and stability: Methionine is converted to methionine sulfoxide, even at low temperature and in samples frozen at -20 oC.
Reported values: <0.5 µmol/L.
Intraclass correlation coefficient (ICC): 0.36.
1. Midttun, O., Kvalheim, G., and Ueland, P.M. (2013). High-throughput, low-volume, multianalyte quantification of plasma metabolites related to one-carbon metabolism using HPLC-MS/MS. Anal Bioanal Chem 405, 2009-017.
2. Hustad, S., Eussen, S., Midttun, O., Ulvik, A., van de Kant, P.M., Morkrid, L., Gislefoss, R., and Ueland, P.M. (2012). Kinetic modeling of storage effects on biomarkers related to B vitamin status and one-carbon metabolism. Clin Chem 58, 402-410