Serological Interference Related to Intravenous Immunoglobulins: A Case of False Immunization Against Hepatitis B...

Intravenous immunoglobulins (IVIG) are derived from pooled plasma obtained from thousands of donors and are widely used in the treatment of inflammatory, infectious, and immunodeficiency disorders. Due to their origin, these preparations may contain antibodies directed against various infectious agents. Their administration can therefore result in passive transfer of antibodies, potentially interfering with the interpretation of certain serological tests.

We report a case of false-positive anti-HBs antibodies observed following IVIG administration in a patient with no prior history of vaccination, who was being followed for polyarteritis nodosa with resistance to first- and second-line therapies.Serological testing was performed as part of a pre-therapeutic workup prior to initiation of tocilizumab. Subsequent follow-up tests demonstrated a progressive decline in antibody titres, consistent with the clearance of passively transferred immunoglobulins.

Passive transfer of anti-HBs and anti-HBc antibodies, as well as other antibodies targeting infectious agents or autoimmune antigens following IVIG administration, has been previously described in the literature. This situation is of particular clinical relevance in patients who are candidates for immunosuppressive therapy, which may induce reactivation of certain pathogens. Misinterpretation of these results may lead either to unnecessary prophylactic treatment or to inappropriate modification or delay of essential immunosuppressive therapy. To avoid misleading results, it is recommended to perform baseline serological screening prior to IVIG initiation, to store a reference serum sample for potential retrospective analysis, and, in patients receiving high doses, to avoid IgG-based serological assays in favour of diagnostic methods such as polymerase chain reaction.

Increased awareness among clinicians and laboratory specialists is essential to prevent unnecessary investigations and delays in appropriate patient management.

False-positive serological results following intravenous immunoglobulin (IVIG) therapy, may lead to diagnostic confusion and unnecessary investigations.Internists should consider recent IVIG administration when interpreting serological tests, to avoid misdiagnosis and inappropriate management.Careful timing and interpretation of serological tests in patients receiving IVIG is essential.