Abstract: Objective:To analyze the reasons for unreliable outcome resulting from the plasmas with high D-dimer(D-D) concentration diluted to 8 times,and explore the optimal dilution of the plasmas for D-D test.Methods:The D-D standard curve was derived from the six concentration levels of D-D standard plasma by a customary way.The standards and the patient plasma were diluted to 2 times,4 times and 8 times in a coagulation analyzer or by manual,and then they were analyzed in a calibrated analyzer;The results in the analyzer and by manual were statistically compared.Results:The standard curve of D-D was similar to the letter S.The D-D concentration when the plasma was diluted to 8 times in the analyzer was decreased significantly(P0.01),compared with that when diluted to 2 times by manual.However,there was not statistical difference between the plasma and its dilution to 2 times or between the same dilutions in both modes(P0.05).Conclusions:The higher the dilution is,the more obvious the difference will be.Therefore,the plasma with high D-D concentration should be diluted as less times as it can be determined in order to assure the reliability of D-D value.