Abstract: Objective To investigate the influencing factors of grey-zone results in anti-hepatitis C virus（HCV） antibody determination by chemiluminescence microparticle immunoassay（CMIA）. Methods Totally，183 patients in the grey-zone（S/CO value was 1.0-5.0）（grey-zone group） were enrolled for anti-HCV antibody determination by CMIA. There were 33 cases of malignant tumors，16 cases of hepatitis B，16 cases of cholecystitis，13 cases of gallstones，13 cases of benign tumors，11 cases of liver cirrhosis，9 cases of bile duct stones，9 cases of cholangitis and 63 cases of other diseases. Totally，33 healthy subjects with negative results of anti-HCV antibody（S/CO value <1.0） were enrolled as control group. Reverse transcription-polymerase chain reaction（RT-PCR） was used to determine HCV RNA. The clinical data of all the patients and the laboratory determination results of all the subjects were collected，and the anti-HCV antibody determination results by enzyme-linked immunosorbent assay（ELISA） and electrochemiluminescence immunoassay were recorded. Multiple linear regression analysis was used to investigate the influencing factors of anti-HCV antibody determination results. Results The results of HCV RNA determination in grey-zone group were negative. The consistency of CMIA and electrochemiluminescence immunoassay with RT-PCR was 100.00%，and the consistency of ELISA with RT-PCR was 97.81%. The results of multiple linear regression analysis showed that the S/CO value of anti-HCV antibody determined by CMIA could be increased by benign tumors（t=2.080，P=0.039） and be decreased by osmolality（t=-2.238，P=0.027）. The other indicators had no effect on the determination of anti-HCV antibody by CMIA（P>0.05）. There was no statistical significance in serum osmolality between grey-zone group and control group（P>0.05）. Conclusions When using CMIA to determine the samples from patients with a history of benign tumors，the S/CO value may increase，resulting in grey-zone results.

Key words: Hepatitis C virus, Chemiluminescence microparticle immunoassay, Antibody, Grey-zone