Viral load monitoring

For HCV RNA measurement, different standardized
quantification assays, based on signal amplification [branched
DNA(bDNA) assay] and target amplification [reversetranscription
PCR (RT-PCR)] with different sensitivities are
commercially available. The development of a World Health
Organization HCV international unit (IU) standard has
contributed to a better accuracy and comparability of results
obtained by different assays. However, since standardization to
IU and the calibration of assay sensitivity are based on genotype
1a (deLeuw 2011), relative quantification results may vary
among assays. Using the WHO international standard, a VL of 2
millions copies/mL (the cut-off value predictive for therapeutic
success in early clinical trials with IFN) was found to correspond
to 800 000 IU/mL. Currently a cut-off of 400 000-800 000 IU/ml
separate low from high VL. Further studies have found that
patients with low baseline HCV RNA levels have a 15-39% better
response rate, a finding that is consistent across trials using
different formulations and dosages of IFN (Strader 2004).