Anti‐hepatitis C virus (HCV) screening at a Canadian Red Cross center: significance of a positive c100 HCV enzyme‐linked immunosorbent assay

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Abstract
The c100 hepatitis C virus (HCV) enzyme‐linked immunosorbent assay (ELISA) has been used to screen blood donors to prevent transfusion‐ associated non‐A, non‐B hepatitis. This test is not specific, and only about 25 percent of c100 HCV ELISA‐positive blood samples appear to transmit hepatitis C. However, the intensity of the ELISA (sample/cutoff ratio [S/C], greater than 2) could identify a subpopulation of donors that are at high risk for transmitting hepatitis. Blood samples from 20,186 volunteer blood donors at a Canadian Red Cross blood transfusion center were screened for antibodies to HCV using the c100 HCV ELISA. Fifty‐nine (0.3%) of these donors were repeatably reactive on ELISA. When their samples were tested with the c100 recombinant immunoblot assay (RIBA) and second‐ generation RIBA (RIBA‐2), 26 (44%) and 31 (52%) samples, respectively, were found to be positive. Thirty‐three of the 59 ELISA‐reactive donors had an S/C greater than 2. Of these 33 donors, 30 (91%) had elevated alanine aminotransferase (ALT), 27 (82%) were RIBA‐2 positive, and 22 (67%) had risk factors for hepatitis. In contrast, of the 26 ELISA‐ reactive donors with S/C less than 2, only 7 (27%) had elevated ALT, and 4 (15%) were RIBA‐2 positive and also had high risk factors for hepatitis. Thus, while the HCV ELISA may lack specificity, its intensity can serve to identify a subgroup of donors that are at high risk for transmitting hepatitis.