[Diagnosis and biological surveillance of hepatitis C virus infections]

HCV-specific laboratory assays are broadly used to establish the diagnosis, to survey viral replication and to monitor anti-viral treatments. Third-generation ELISA's have an excellent sensitivity well adapted to the early diagnosis. Positive or dubious screening tests must be controlled on a second blood sample. We recommend the use of an immunoblot assay for this control. Regular survey of the immunoblot profile may facilitate the identification of recent infections and help distinguish between active or resolutive infections. PCR assays which detect HCV ARN in serum are very usefull to decide and monitor anti-viral treatments. Their cut-off is usually in the range of 100 genomes/mL. Quantitative assays to measure viral load may also rely on PCR technology or be based on the so-called "branched DNA" technology slightly less sensitive. Genotyping or serotyping of HCV is crucial to adapt specific treatment protocols to the less responsive genotypes 1a et 1b. Cloning and sequencing of HCV isolates is necessary to explore nosocomial clusters of infections or intra-familial cases.