Significance of IgM anti‐hepatitis D virus (HDV) in chronic HDV infection

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Abstract
Intrahepatic hepatitis D virus (HDV) antigen (HDAg) and serum HDV RNA are excellent markers of active HDV replication but the relation of IgM anti‐HDV to HDV replication and histological activity is less certain. To further elucidate the significance of serum IgM anti‐HDV, 90 paired sera and liver biopsies from 64 patients sero‐positive for total antibody to HDV were analysed for IgM anti‐HDV, intrahepatic HDAg expression, and histological inflammatory activity. IgM anti‐HDV was strongly associated with intrahepatic HDAg expression with a sensitivity of 94.1% but the assay lacked specificity since 14 out of 22 cases negative for intrahepatic HDAg were also positive for IgM anti‐HDV. In 20 patients in whom follow‐up biopsies and paired sera were available, two patients lost intrahepatic HDAg but paired serum remained IgM anti‐HDV positive. Although the presence of serum IgM anti‐HDV correlated significantly with a higher histological inflammatory activity (P = 0.001), there was a considerable overlap with the group seronegative for IgM anti‐HDV, again indicating a poor specificity. This lack of specificity of IgM anti‐HDV for both HDV replication and histological activity indicates that this assay provides no additional information over and above assay for total antibody to HDV.