Automated quantitative analysis of hepatitis B virus DNA by using the cobas Amplicor HBV Monitor test

A highly sensitive method of quantitative analysis of hepatitis B virus (HB V) DNA in serum, the Cobas Amplicor HBV Monitor (Cobas-AM) test, was evalua ted. Following a manual extraction of viral DNA, amplification, colorimetri c detection, and quantitative determination are all automatically performed in the Cobas analyzer. Serially diluted samples with known HBV DNA concent rations were analyzed blindly. All samples with a virus concentration of 40 0 copies/ml and 83% of samples with a virus concentration of 100 copies/ml could be detected. A linear correlation between input HBV DNA and measured HBV DNA was seen in the range from 100 to 10(5) copies/ml. The mean coeffic ient of variation was 29.6% for all input levels and 18.9% for HBV DNA conc entrations above 400 copies/ml. Samples with an HBV DNA level above 10(9) c opies/ml could be reproducibly measured after predilution to 10(-4) or 10(- 6) in negative serum; however, the level was underestimated if target DNA a fter dilution was still above the linear range of the assay. Quantitative r esults of the Cobas-AM test were interchangeable with measurements by the m anual microwell plate version of Amplicor HBV Monitor (MWP-AM); the mean ra tio for log Cobas-AM results/log MWP-AM results was 0.97 (standard error of the mean, 0.007) when serum samples from 153 chronic carriers were analyze d. The test should be of value for clinical assessment of chronic carriers and for monitoring the response to antiviral treatment. A limitation is the relatively narrow linear range of the assay, requiring predilution of high -titer (mainly hepatitis B e-antigen-positive) samples.