Homocysteine (Hcy) reagent is a reagent used for quantitative detection of total Hcy in human serum and plasma in vitro. This detection reagent helps in the diagnosis and treatment of patients suspected of hyperhomocysteinemia and homocysteinuria. At present, Hcy has become a recognized biomarker of cardiovascular disease both domestically and internationally. Reaction principle: First, Hcy in the combined or polymerized state (oxidized Hcy) is reduced to free Hcy. Then, free Hcy and serine form cysteine under the action of cysteine sulfide synthase (CBS), and the formed cysteine sulfide forms Hcy, pyruvate, and ammonia under the action of cysteine sulfide lyase (CBL). Pyruvate reacts with NADH (coenzyme) under the action of lactate dehydrogenase (LDH), and the rate of NADH conversion to NAD+conversion at 340nm per minute is directly positively correlated with the concentration of Hcy.