Autozyme Calcium is single reagent system for determination of calcium based on colorimetric method using o-Cresolphthalein Complexone. Autozyme Calcium has one step reconstitution. It involves mixing CPC and Diluent reagent. Calcium can be determined in 5 minutes. Autozyme Calcium has minimum reagent waste since working solution can be prepared according to the need. Interference of Mg and Fe is negligible. Lipemic samples do not require any specific treatment. Calcium forms a purple color complex with cresol phthalein complexone in alkaline medium. This complex absorbs light at 575 (570 – 580) nm. The intensity of the color is directly proportional to the calcium concentration in the specimen.