Yes, intravenous immunoglobulin therapy may cause false positives on antibody-based tests. This is because immune response to IV IgG therapy is highly variable and there is no absolute/definitive clinical guidelines for Ig levels to return to baseline after infusion.
To avoid false positive results, providers using IV Ig treatment for patients should test Total Immunoglobulins before ordering antibody-based tests.
In determining when to test Total Immunoglobulins after IV IgG treatment, a simple explanation would be to test Total Immunoglobulins right before the person is due for their next IV IgG infusion.
Another option would be to wait approximately six weeks. In a narrative review of false interpretation of diagnostic serology tests for patients treated with IV IgG, Bright et al. (2015) conclude that "IgG antibody tests within six weeks of IgG administration are generally unhelpful and sometimes dangerously misleading."
