HBc antigen immunodetection: Formalin versus Bouin's solution fixation

Immunohistochemical detection of hepatitis B core antigen (HBcAg), a reliab le marker of hepatitis B virus (HBV) replication, is routinely performed in chronic hepatitis B on paraffin-embedded liver biopsies regardless of fixa tion technique. Due to sensitivity discrepancies observed in the HbcAg immu nodetection, we prospectively investigated the role of the type of fixative solution (formalin versus Bouin's solution) in 32 consecutive patients wit h chronic hepatitis B. Results were compared with those of serum HBV-DNA de termined by liquid hybridization. The biopsy core was divided into two part s, one immersed in 4% buffered formalin and the other in Bouin Alien's solu tion for 24 hours before paraffin embedding. HbcAg immunodetection, perform ed with a rabbit polyclonal antibody, was revealed by the streptavidin-biot in peroxidase method. Nuclear HBcAg positivity, observed in 21 cases, was s olely confined to formalin fixed material in five cases and was more intens e after formalin than after Bouin's solution fixation in the 16 other cases . Cytoplasmic HBcAg positivity, observed in 15 cases, was solely confined t o formalin fixed material in 12. Eleven cases remained negative whichever t he fixation, seven of these being also serum HBV-DNA negative. Conversely, all but three cases positive by immunohistochemistry were serum HBV-DNA pos itive, the three exceptions being serum anti-HBe positive. In conclusion, f ormalin fixation is significantly superior to Bouin's solution fixation for HBcAg immunodetection. With regard to HBV replication, the sensitivity of this detection is at least similar to that obtained with serum HBV-DNA dete rmined by liquid hybridization.