Monitoring low level hepatitis B virus by a newly developed sensitive test.

We have recently developed a sensitive quantitative test for hepatitis B virus (HBV) DNA using a real-time polymerase chain reaction (HBV RTD DIRECT), which can detect HBV DNA levels as low as 100.7 copies/ml. The aim of this study was to explore the significance of viremia changes below the detection limit of the other currently developed sensitive assays, transcription-mediated amplification and hybridization protection assay (TMA-HPA) and Amplicor HBV Monitor. The subjects consisted of 11 patients with chronic liver disease type B who showed undetectable test results of HBV DNA by TMA-HPA or Amplicor HBV Monitor during the observation period. A total of 150 serial serum samples were examined for viremia level by HBV RTD DIRECT: 139 were positive and 11 were negative. HBV RTD DIRECT could detect viremia in 72 of 78 serum samples negative for HBV DNA by TMA-HPA, or in 38 of 43 serum samples negative for HBV DNA by Amplicor HBV Monitor. The HBV DNA level was gradually increased from its lowest level before the spontaneous reactivation of hepatitis or the emergence of YMDD mutant during lamivudine treatment. However, such a phenomenon was not revealed by either TMA-HPA or the Amplicor HBV Monitor test.