Discussion

Immunoassays for the detection of HEV IgM and IgG antibodies are widely used because of their ease of use and comparatively low cost. The problem, however, is that the tests have different sensitivity and specificity and give qualitative, semi-quantitative or quantitative results 8,11,12,14-16. The differential performance of anti-HEV IgG assays has important implications for seroprevalence estimates 17. A WHO reference serum (NISBSC 95/584) for standardizing HEV antibody tests has been available for several years 18 and could help to improve assay comparability.
In this study, the LIAISON Murex anti-HEV IgG CLIA showed consistent results with the recom Well HEV IgG ELISA used as a reference. These assays provide quantitative results. The LIAISON Murex Anti-HEV IgG test is aligned with the WHO standard. In general, both assays appear to be suitable for seroprevalence studies. The CLIA has the advantage of being fully automated.
HEV IgM antibody test results are more heterogeneous and require detailed discussion. The highest number of HEV IgM-positive samples was found with the recom Well HEV ELISA. However, HEV RNA could not be detected in any of the 17 samples that were reactive in this test but not in the DiaSorin assay. Therefore, a post-acute infection status, persistent IgM or even a false-positive IgM detection is assumed. If therecom Well HEV IgM ELISA is used in combination with the HEV IgMrecom Line immunoblot, as recommended by the manufacturer, the number of IgM detections is reduced about almost 50% (27 out of 53 positive samples are confirmed by immunoblot). Eight of 17 samples found to be reactive in the recom Well HEV IgM ELISA were concordantly negative in the recom Line HEV IgM blot and in the Diasorin and Wantai IgM assays (supplementary material). Recently, good agreement was reported between HEV antibody tests from the latter two manufacturers9.
In four of the 53 IgM-positive sera, no corresponding IgG antibodies were detectable (quoted as isolated HEV IgM). Two of these samples were reactive in the recom Well HEV IgM ELISA, the recom Line HEV IgM immunoblot and the CLIA, while two samples were reactive only in therecom Well HEV IgM test (supplementary material). It is suspected that these two samples were false positive for HEV IgM. This finding underlines the importance of the recom Line HEV IgM immunoblot for the verification of reactive ELISA results. In general, detection of isolated HEV IgM should prompt confirmatory and follow-up testing.
The investigation of a limited number of samples with serologically suspected acute EBV/CMV infection revealed possible HEV-IgM cross-reactivity confirming the results of a previous study19. This phenomenon is most likely due to polyclonal B-cell stimulation associated with herpesvirus infection19. Therefore, patients with isolated HEV IgM should be followed up after a few weeks. If necessary, EBV and CMV serostatus should also be determined.