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A pattern of 5‐1‐1 and c100‐3 only on hepatitis C virus (HCV) recombinant immunoblot assay does not reflect HCV infection in blood donors

Current criteria for a reactive (positive) interpretation on hepatitis C virus (HCV) recombinant immunoblot assay (RIBA) require > or = 1+ reactivity to at least two of the four HCV antigens present in the assay. Given that 5‐1‐1 is a subcomponent of c100‐3, there is concern that donor samples reacting only with these two antigens (and not with c22‐3 or c33c) could be incorrectly classified as positive on the basis of limited reactivity to only one HCV gene product. It is determined that 0.23 to 0.44 percent of HCV enzyme immunoassay‐repeatably reactive donor sera demonstrate a pattern of 5‐1‐1 and c100‐3 only on RIBA. Evaluation of six such donor sera using peptide enzyme immunoassays spanning the c100‐3 antigen showed highly restricted reactivity to the 5‐1‐1 N‐terminal region of c100‐3, in contrast to broad 5‐1‐1 and c100‐ 3 C‐terminal peptide reactivity observed in the majority of donor sera with other positive RIBA patterns. HCV polymerase chain reaction and follow‐up serologic evaluations of four of these donors indicated the absence of viremia or evolving seroconversion in all cases. It is concluded that, in the blood donor setting, a pattern of only 5‐1‐1 and c100‐3 reactivity is typically not indicative of HCV infection. To avoid overinterpretation, it is recommended that RIBA grading criteria be revised to require reactivity to two or more HCV‐encoded gene products.