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.