High proportion of false positive reactions among donors with anti‐HCV antibodies in a low prevalence area

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Abstract
Among 39, 656 voluntary blood donors in Okinawa Prefecture, Japan, 115 (0.29%) were repeatedly reactive for antibody to hepatitis C virus (anti‐HCV) by second generation (2nd‐gen) passive hemagglutination assay (PHA). Positive serum samples were tested for anti‐HCV using three different enzyme immunosorbent assays (ELISAs; Abbott 2nd EIA, UBI‐HCV‐EIA, JCC‐2) and for HCV‐RNA by the polymerase chain reaction (PCR).The 115 2nd‐gen PHA‐positive sera were divided into three groups according to the agglutination titers; >210 (high titer group), 27−29 (median), 25−26 (low). All but one serum (44/45) in the high PHA titer group reacted in each of the three second screening ELISAs. Furthermore, 43 (97.7%) of the 44 sera contained HCV‐RNA by PCR. In the median titer group, 11 of the 13 samples tested were positive by each of the three ELSIAs, and 4 (36.4%) of the 11 showed reaction by PCR. On the other hand, all of the 38 sera tested in the low titer group were negative for HCV‐RNA by PCR, and 24 of the 38 were also negative by each of the three ELISAs.Most of the low titer positive reactions in the 2nd‐gen agglutination assay seemed to be false positive. In Okinawa Prefecture, the prevalence of anti‐HCV among blood donors is much lower than in the rest of Japan (0.29% vs. 1.11%). Moreover, a significant proportion of these sera were low titer by the PHA assay. The difference in the genuine anti‐HCV‐positive rate, or the prevalence of HCV carriage between Okinawa Prefecture and the rest of Japan may therefore be even greater than is presently assumed.