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Different sensitivity of chemiluminescent immunoassay for the detection of HBsAg

Abstract number: p649

Rodella  A., Terlenghi  L., Cariani  E., Manca  N.

Background and aims: 

Sensitivity is the fundamental analytical requisite of assays for the surface antigen (HBsAg) of hepatitis B virus (HBV), since the determination of HBsAg is carried out both for blood donation screening and for screening and diagnosis of the general population; assay specificity is also important in low-prevalence settings. We aimed to investigate the diagnostic accuracy of two automated chemiluminescent immunoassays for HBsAg (Abbott Architect and Ortho Vitros) on selected repository specimens.

Materials and methods: 

We selected 94 serum samples who gave a repeat reactivity by our routine screening assay for HBsAg (Abbott AxSYM HBsAg) and that were classified as true or false positives according to the result of a confirmatory neutralization assay and/or by serological or clinical criteria. All specimens were assayed under code by Architect and Vitros HBsAg in a different lab and the results were reported to our Center.

Results: 

The samples were divided into two groups: (a) 30 false positives by AxSYM, all negative by Vitros and 28 (93.3%) negative by Architect; (b) 64 true positives (57 neutralized, 3 viremic, 4 positive for other markers and with a history of HBV infection). The Architect assay gave a positive result on 63 specimens, the only negative being a patient clearing HBsAg after an acute infection. In contrast, the Vitros assay was positive only in 34 cases, grayzone negative in 4 and negative in 26. Interestingly, 7 of the samples negative by Vitros showed a strong reactivity by Architect, [sample/cutoff (S/CO) ratios from 100 to >5000], and three showed also a strong reactivity for anti-HBs (>240 mUI/mL), suggesting the possible presence of surface antigens escape mutations.

Conclusions: 

The assay for HBsAg on the Architect analyser was accurate in the discrimination of true from false positives, whereas the Vitros assay gave a surprisingly high rate of false negatives. In 19 cases this was probably due to a lower analytical sensitivity, but for the remaining seven specimens, showing a strong positivity for HBsAg by both AxSYM and Architect HBsAg, the negativity by Vitros may be related to its limited capability to recognize HBsAg mutants, as reported in the literature. In our opinion, it is urgent to clarify the prevalence and clinical impact of surface antigen variants in the current epidemiological setting in Italy as well as in the other countries in which anti-hepatitis B vaccination policies are established.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Subject:
Location: Oxford, UK
Presentation type:
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