Simplified simultaneous assay of total plasma homocysteine and methionine by HPLC and pulsed integrated amperometry.

known naturally occurring degradation product may be of interest with respect to the etiology of neural tube defects or the homocysteinemia that is associated with this variant. At a more practical level, the comparative evaluation of the two assays reported here indicates that folate concentrations are not being measured accurately by one of the assays in the 5% to 15% of people who are homozygous for the thermolabile variant.