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False negative immunoblot result during long period before seroconversion in a hepatitis C virus infected intravenous drug user

In our case an HCV third-generation EIA screening test gave a borderline reactive result but a confirmatory immunoblot tests did not show any visible reaction. In a second sample, taken two months later, a significant increase in the HCV EIA S/CO ratio was observed but both immunoblots remained negative. The difference in the test sensitivity observed in this case between EIA and immunoblot could be explained by lower sensitivity of some immunoblot assays and could be an explanation for the “ delayed seroconversion” . An additional explanation for the difference in sensitivity between the EIA and the immunoblots observed in this study could possibly be related to HCV genotype 3a which is typically grouped in Switzerland in the IDU community and has to be further elucidated. This case shows that false negative HCV immunoblot results after reactive screening results are possible. Following the CDC Laboratory algorithm for antibody to hepatitis C virus (anti-HCV) testing and result reporting, interpreting false negative immunoblot as true negative can lead to missing an active HCV infection in some individuals who have weak or restricted virus-specific antibody responses, such as intravenous drug users. Therefore we suggest that such persons cannot be considered uninfected solely on the basis of a negative immunoblot result. To avoid missing an active HCV infection in IDUs, a negative immunoblot result should be followed by nucleic acid amplification testing (NAT). This approach would optimize early HCV diagnosis in terms of opportunities for earlier treatment, source identification and introduction of preventive measures.

false negative immunoblot; hepatitis C virus; injecting drug user

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