Comparison of four newly developed immunoblot assays with RIBA II for detection of HCV antibodies

ELISA, the usual screening test for HCV infection, may yield nonspecific results. Most laboratories, therefore, for corroboration perform PCR. However, a negative HCV-PCR does not prove nonspecifity of the initial ELISA test and therefore an immunoblot has to be performed. RIBA-II was used for that purpose for several years, but suffers from a high number of indeterminate results. We therefore compared RIBA II results of 75 sera with those of RIBA III, Matrix, Western Blot (Murex) and INNO-LIA tests. Of 34 sera that were positive in RIBA II, all were also positive in the four other immunoblots. Similarly, these 4 tests showed concordantly positive results in 13 of 27 RIBA II indeterminate sera. In the remaining 14 (RIBA II indeterminate) sera the four immunoblots displayed no uniform results but various combinations of positive, indeterminate and even negative results. Similar results were found with 13 RIBA II negative (ELISA positive) sera. These data may indicate less sensitivity as well as some nonspecificity of some of the immunoblots. In general, however, the four newly developed immunoblots proved to be more sensitive than RIBA II. This obviously is not caused by the inclusion of the NS₅-antigen but by improvement of the conventional antigens. Only one serum was found in which the NS₅-band was crucial for its positivity. In conclusion, for corroboration of some HCV-ELISA positive, PCR negative sera, more than one immunoblot may be necessary.