The LOD and linear range of the cobas HBV test

The LOD and linear range of the cobas HBV test using the cobas 4800 system in this study were similar to those provided by the manufacturer. We found a strong correlation between the results of the cobas HBV test and CAP/CTM v2.0 systems; however, 7.7% of samples yielded detectable results only with the cobas HBV test, and 3.2% of samples yielded detectable results only with CAP/CTM v2.0. In particular, 3 samples that showed negative results for HBsAg and anti-HBc Ab were detected ( < 10 IU/mL) using only the cobas HBV test. The presence of HBV DNA in these 3 samples was confirmed using sequencing (data not shown). Factors that contribute to differences in HBV DNA load include the B genotype [6], low HBV load [7], and mutations in the precore and core promotor regions, including a tyrosine-methionine-aspartate–aspartate mutation [8,9]. The detection sensitivity for HBV mutations in the precore and core promotor regions differ depending on the assay. The correlation between the two reagents in cases of HBV DNA <2000 IU/mL was worse than that for HBV DNA >2000 IU/mL in this study. Detection of low viral load is important, because the persistence of low HBV DNA levels after treatment correlates with relapse, recurrence, and drug resistance [10,11]. Moreover, the guidelines for the management of chronic hepatitis B recommend that treatment should be promptly initiated in patients with HBV DNA concentrations of >20,000 IU/mL; however, the available guidelines vary in their recommendations for patients with HBV DNA concentrations between 2000 and 20,000 IU/mL [[11], [12], [13], [14], [15]]. Furthermore, to determine the virological response on interferon/pegylated-interferon therapy or nucleos(t)ide analogues, HBV DNA levels below 2000 IU/mL are necessary [[13], [14], [15]]. Of note, hepatitis B e-antigen–negative patients with an HBV DNA concentration of <2000 IU/mL are at reduced risk for hepatocellular carcinoma [16]. The cobas HBV tests accompanied by the cobas 4800/6800/8800 systems have received the Conformité Européenne label; however, only two of the tests, the cobas HBV test combined with the cobas® 6800/8800 systems, have been approved by the United States Food and Drug Administration. The systems using the cobas HBV test and CAP/CTM v2.0 are both based on fully automated nucleic istradefylline extraction and purification followed by PCR co-amplification of the HBV template and an added internal quantitation standard and detection by the use of sequence-specific forward and reverse primers that are selected to highly conserved precore and core regions of the HBV genome [17]. However, the cobas HBV test has a broad range of quantification and a lower LOD than CAP/CTM v2.0, owing to modifications made to the various steps of the process, including to the composition of reagents, primer sequence, and detection equipment. Moreover, a major advantage of the cobas HBV test using the cobas 4800 system is its low turnaround time. In this study, the times taken to test 24 and 96 samples using the cobas HBV test were 2 h 45 min and 4 h 5 min, respectively. On the other hand, the corresponding times using CAP/CTM v2.0 were 4 h 30 min and 11 h 15 min, respectively. Lastly, the time taken to identify the barcode is reduced, owing to the incorporation of a board barcode scanner, unlike in the COBAS AmpliPrep/TaqMan system. However, the cobas 4800 system is not fully automated, and the samples need to be transferred manually from the cobas x 480 instrument to the cobas z 480 analyzer [18].
Competing interests
Ethical approval
Acknowledgements All components of the Cobas HBV test and CAP/CTM v2.0, including disposables and reagents, were provided or funded by Roche.
Introduction Chronic hepatitis B virus (HBV) infection is a major global public health issue and one of the highest risk factors for hepatitis, cirrhosis and hepatocellular carcinoma (HCC) (Schweitzer et al., 2015). Recent Global Burden of Disease estimates indicate a high morbidity and mortality attributable to chronic HBV infection, despite decreases over the past decades (Levrero and Zucman-Rossi, 2016, Vos et al., 2015). To date, various strategies have been used to treat HBV infection, but their clinical outcomes remain suboptimal (Zeisel et al., 2015). Five nucleos(t)ide analogues (NAs) (lamivudine, adefovir dipivoxil, entecavir, telbivudine, and tenofovir) acting as competitive inhibitors of the reverse transcription step of HBV DNA synthesis have been approved for the treatment of HBV infection. However, a potential limitation of NAs therapy is that drug resistance mutation could seriously reduce viral sensitivity to NAs therapy (Durantel and Zoulim, 2016). Another limitation is that it has no inhibitory effect on HBeAg or HBsAg expression and it is inefficient in promoting HBeAg/HBsAg seroconversion (Gish et al., 2015a). Increasing evidence indicates that high serum HBsAg and HBeAg levels are associated with the occurrence of HCC (Sunami et al., 2016, Liu et al., 2014, Liu et al., 2016).