Laboratory Issues

The major laboratory issue in HBV DNA quantitation is the widely divergent results obtained with the different assays. To address interassay differences, the World Health Organization (WHO) developed an international standard for HBV DNA, designated 97/746.22 The WHO standard is a lyophilized plasma specimen that has been analyzed by several laboratories using different nucleic acid tests and has an assigned potency of 106 international units (IU)/ml. In the future, all new assays for HBV DNA should be calibrated against the WHO standard and the results reported in IU/ml. In the interim, laboratories should be aware of the substantial interassay differences in quantitative results.

The lack of FDA-cleared test kits for HBV DNA places increased burden on laboratories to verify the test performance characteristics. Unfortunately, there are no formal proficiency surveys for HBV nucleic acid tests, although control and reference materials are available from several companies.

Serum and plasma, with EDTA or citrate dextrose as an anticoagulant, are acceptable specimens for most nucleic acid tests for HBV. In the absence of stability data, samples for nucleic acid testing should be processed to separate blood cells from the plasma or serum within 6 hours of collection and either tested within 24 hours or stored at -70°C. In one study HBV DNA was stable in separated serum samples for at least 5 days when specimens were stored at

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