The presence of rheumatoid factor in sera from anti-HCV positive blood donors interferes with the detection of HCV-specific IgM. Trent HCV Study Group.

BACKGROUND/AIMS: IgM anti-HCV has been reported as a useful marker of disease activity and of likely response to interferon therapy in patients with chronic hepatitis C virus infection. Sera from patients with hepatitis C virus infection may contain rheumatoid factor. This study was designed to investigate the possible effect of rheumatoid factor in an IgM anti-HCV assay.

METHODS

Sera from 75 blood donors with chronic hepatitis C virus infection were tested for the presence of IgM anti-HCV using a core-derived peptide as antigen, before and after removal of IgG. These sera and appropriate control sera were also tested for the presence of rheumatoid factor.

RESULTS

Removal of IgG prior to IgM testing resulted in a significant loss of reactivity in the IgM anti-HCV assay in 30/41 sera that were positive in this assay when tested untreated. Seventy per cent of anti-HCV positive sera were also positive for rheumatoid factor.

CONCLUSIONS

Rheumatoid factor causes significant false positive reactivity in IgM anti-HCV detection assays. The results of assays that do not account for this interference should be viewed with caution.