Total plasma homocysteine as part of the routine aminogram by ion-exchange chromatography.

Ion-exchange chromatography (IEC) with ninhydrin post-column derivatisation is the only technique available for the assay of total, (free plus bound), cysteine and homocysteine which also enables the routine measurement of all other commonly occurring amino acids. IEC assay of total cysteine and homocysteine typically involves incubating buffered plasma for 60 minutes at 37 degrees C with dithiothreitol (DTT), but these assay conditions significantly extend total analysis time and compromise other amino acid values, notably glutamine and glutamate. However, it is possible to carry out the DTT reduction in plasma virtually instantaneously and without additional buffering, thus preserving the integrity of other diagnostically important amino acids. Assay precision is adequate for cardiovascular risk assessment.