Immunoassay Blocking Agents: Reducing False Results

PRECISION STARTS WITH CLEAN SIGNALS

Immunoassay blockers are essential tools for reducing false results caused by non- specific binding and antibody interference— such as HAMA and rheumatoid factor (RF). Used in ELISA and lateral flow assays, blockers improve assay accuracy by increasing the signal-to-noise ratio. They are especially important across common assay types—sandwich antigen detection, antibody capture, and competitive ELISAs—where selecting high-affinity antibodies and the right blocking agents is critical to achieving high specificity and sensitivity. Since COVID, many assay developers have reported increased immunoassay interference. One likely contributor is the rise in circulating autoantibodies—especially IgM rheumatoid factor (RF)—following SARS-CoV-2 infection. Studies have shown that COVID-19, like other respiratory viral infections, can trigger lasting immune dysregulation, leading to the emergence of polyreactive antibodies with broad binding capabilities. ⎕ These antibodies, particularly IgM-RF, can bind to the Fc region of assay antibodies—especially those derived from animal sources—forming immune complexes that mimic true signal generation. The result: false positives, elevated background, and reduced assay specificity, ultimately undermining clinical confidence and diagnostic reliability. As this challenge grows, many assay developers are re- evaluating their blocking strategies and exploring new solutions to mitigate interference in increasingly complex, post-COVID sample populations.

Detection Antibody

Detector Label

Capture Antibodies

IgM RF

IMMUNE COMPLEX MIMICKING TRUE ASSAY SIGNAL

⎕ Mohan, A., et al. (2023). Navigating the Post-COVID-19 Immunological Era: Understanding Long COVID-19 and Immune Response. Life 13(11), 2121. https://doi.org/10.3390/life13112121