There are many types of anticoagulants, and it is especially important to choose the right anticoagulant correctly. The anticoagulant for the four items of coagulation should be 0.109 mol/L citrulline, and the anticoagulants used, EDTA, i.e., sodium ethylenediaminetetraacetic acid and sodium oxalate, are not suitable for the four items of coagulation because EDTA can inhibit or interfere with the polymerization of fibrin monomers during the formation of fibrin clots, and sodium oxalate can cause the calcium ions in the blood to form an insoluble precipitate, which will affect the observation of photoelectric endpoints during the determination of the hemagglutination instrument. observation of the photoelectric endpoint. Because of the protective effect of citrulline on coagulation factors, the International Society of Experimental Hematology ISLH recommends the use of 0.109 mol/L citrulline solution as an anticoagulant for coagulation factor assays.