Differential diagnosis of acute HBsAg positive hepatitis using IgM anti-HBc by a rapid, fully automated microparticle enzyme immunoassay.

Background/aims: We determined the diagnostic significance of IgM anti-HBc by a rapid, fully automated microparticle enzyme immunoassay (IMx CORE-M) in acute HBsAg positive hepatitis.

Methods: We studied prospectively for at least 6 months 100 patients with acute self-limited hepatitis B (group A) and 40 patients with acute hepatitis superimposed on histologically confirmed chronic hepatitis B (group B). On admission, all patients in group A were positive and those in group B were negative for IgM anti-HBc by a commercially available enzyme immunoassay.

Results: Based on the assay criteria, the rates of IMx CORE-M (> 1.2) positive serum samples on admission, 4, 12 and 24 weeks later were: in group A: 100%, 95%, 72%, 44% and in group B: 20%, 27.5%, 17.5%, and 15%, respectively. Misclassification was observed in 20-27.5% of the acute on chronic hepatitis B cases. However, the mean IMx CORE-M index value was found to be significantly higher in group A during the whole follow-up. In particular, on admission the mean IMx CORE-M index value was 2.504 +/- 0.435 (range: 1.508-3.482) in group A and 0.747 +/- 0.346 (range: 0.062-1.384) in group B (p < 0.001). Discriminant function analysis showed that the cutoff level between the two groups for IMxCORE-M index on admission was 1.5. Four to 12 weeks from admission, in the group with acute on chronic hepatitis B cases, 13 patients with HDV and/or HCV superinfection had significantly lower IMx-CORE M index values compared with 27 patients with acute hepatitis due to exacerbation of chronic hepatitis B.

Conclusions: IMx CORE-M appears to be an accurate diagnostic test to differentiate acute from acute on chronic HBsAg positive hepatitis, but the cut-off level seems to be higher (1.5 instead of 1.2).