ASSAY OF PLASMA HOMOCYSTEINE - LIGHT SENSITIVITY OF THE FLUORESCENT 7-BENZO-2-OXA-1,3-DIAZOLE-4-SULFONIC ACID-DERIVATIVE, AND USE OF APPROPRIATE CALIBRATORS

The recognition of homocysteine as a vascular risk factor has led to i ncreased clinical interest in assaying plasma homocysteine concentrati ons, Our aim was to improve the reliability of a widely used assay bas ed on HPLC of the fluorescent 7-benzo-2-oxa-1,3-diazole-4-sulfonic aci d (SBD) derivative, We found that SBD derivatives of homocysteine, cys teine, and N-acetylhomocysteine were highly unstable in light but esse ntially stable in the dark for several hours at either 0 degrees C or 25 degrees C. As our primary calibrator, we chose homocystine added to human serum for more consistent results than homocysteine or homocyst ine in an aqueous buffer. N-acetylcysteine was effective as an interna l recovery standard, We observed a previously unreported peak with a p rolonged elution time in some plasma samples from subjects who had ing ested methionine. Our findings suggest improvements in this and other assay procedures for plasma homocysteine.