Abstract: Objective　To investigate the influence factors of determining serum mitochondrial aspartate aminotransferase（m-AST） by immune suppression method.   Methods　The determinations of m-AST and aspartate aminotransferase（AST） in a control group（48 cases with AST≤50 U/L） and a hepatitis group（60 patients with hepatitis） were performed by immune suppression method and enzyme hydrolysis method respectively，and then the m-AST/AST ratios were calculated. The deficiency of cytosolic aspartate aminotransferase（c-AST） antibody in the immune suppression method reagents was confirmed through the complementary c-AST antibody test. Results　In the control group，the m-AST value by immune suppression method was significantly higher than that by enzyme hydrolysis method（P＜0.01），while in the hepatitis group，the m-AST value by immune suppression method was significantly lower than that by enzyme hydrolysis method（P＜0.01）. By the immune suppression method，the m-AST/AST ratio had no significant difference between the control group and the hepatitis group（P=0.094）. By the enzyme hydrolysis method，the m-AST/AST ratio in the hepatitis group was significantly higher than that in the control group（P＜0.01）. The correlation of m-AST and AST in the hepatitis group（r=0.969） was higher than that in the control group by immune suppression method（r=0.878），while by the enzyme hydrolysis method，the correlation in the hepatitis group（r=0.856） was lower than thatin the control group（r=0.902）. In the complementary c-AST antibody test of immune suppression method，the values of m-AST decreased with the increase of c-AST antibody being added. Conclusions　If the c-AST antibody is not enough in the immune suppression method reagents，c-AST could notbe inhibited completely，which would cause the decline of the specificity of m-AST test. Using the m-AST/AST ratio，the severity of the liver disease can be analyzed. The antibody concentration of m-AST reagent，the antibody stabilizers and so on should be standardized in order to contribute to the quality control work and improve the clinical application significance of m-AST.

Key words: Aspartate aminotransferase, Mitochondrial isoenzyme, Immune suppression method, Enzyme hydrolysis method, Antibody