EDTA is an aminopolycanboxylic acid that effectively chelate calcium ions in the blood. Calcium removal of calcium removes calcium from the reaction site and prevents and terminates endogenous or exogenous coagulation, preventing blood from clotting. Compared with other anticoagulants, it has little effect on blood cell agglutination and blood cell morphology, so EDTA salts (2K, 3K, 2Na) are usually used as anticoagulants. For general hematology examination, not for blood coagulation, trace elements and PCR.