L-Homocysteine is employed as a reference for in vitro measurement of L-homocysteine in plasma or serum for diagnosis of homocystinuria. Elevated homocysteine levels in blood might also indicate cardiovascular disease.A useful reference standard for measuring L-Homocysteine levels. L-Homocysteine is employed as a reference for in vitro measurement of L-homocysteine in plasma or serum for diagnosis of homocystinuria. Elevated homocysteine levels in blood might also indicate cardiovascular disease. A useful reference standard for measuring L-Homocysteine levels.