Intravenous immunoglobulin infusion contributes to a high incidence of false reactive screen results for human T-lymphotropic virus br

Intravenous immunoglobulin (IVIg) has been increasingly used to treat immunodeficiencies and inflammatory disor-ders. However, IVIg has also been shown to affect a wide range of laboratory testing, including human T-lympho-tropic virus (HTLV) screening. Our laboratory frequently observes false reactive HTLV screens from patients receiving IVIg infusions, however the extent of IVIg contribution to the false reactivity has not been extensively investigated. The objective of this study was to explore the prevalence of HTLV-1/2 infection in patients from the Sydney metropolitan area and evaluate the positive pre-dictive value for HTLV screening test in sera from patients with or without IVIg infusions.HTLV screening test results from sera of 3843 patients referred to Central Sydney Immunology Laboratory be-tween June 2006 and May 2021 were retrospectively analysed. Among 72 (1.9%) sera reactive on screening enzyme-linked immunosorbent assay (ELISA), 62 (86.1%) were from patients receiving IVIg infusions, including 60 collected post-IVIg and two collected pre-IVIg infusions. Only two (3.3%) of the 60 post-IVIg sera were positive on confirmatory western blot. In contrast, in non-IVIg sera, five (50.0%) from the 10 screen-reactive sera were positive on western blot. If positive western blot is used as the reference for determining 'true' HTLV infection, we found the positive predictive value of HTLV screening ELISA in sera collected post-IVIg (3.3%) is considerably lower than that in non-IVIg and pre-IVIg sera (41.7%). The vast ma-jority of false reactive screen results (89.2%) in our study cohort were from sera collected post-IVIg infusion.Our study suggests that the high incidence of falsely reactive results in HTLV screening ELISA could be attrib-uted to IVIg infusion. Hence, collection of sera from pa-tients on IVIg should be avoided and screen-reactive results should be interpreted with greater caution, partic-ularly for patients from non-endemic areas.

Automated summary

This study found that intravenous immunoglobulin (IVIg) infusion could lead to falsely reactive results in human T-lymphotropic virus (HTLV) screening ELISA. Among the screened sera, the vast majority of false reactive results were from patients receiving IVIg infusions. The positive predictive value of HTLV screening ELISA in sera collected post-IVIg was considerably lower than that in non-IVIg and pre-IVIg sera.