Figure 1. Roche system.

Mechanism of biotin interference in Roche immunoassays. The Roche sandwich immunoassay employs a biotinylated antibody to the analyte (thyroid-stimulating hormone, TSH in this example); therefore, excess free biotin displaces antigen-antibody complexes (Ab-Ag), which leads to less ruthenium (Ru2+)-conjugated antibody binding to the solid phase and false depression of analyte measurement. The Roche competitive immunoassay utilizes a complex of biotinylated analyte (thyroxine [T4] in this example) and microparticles with recombinant T4 (rT4) that displace the sample analyte being measured from an antibody-conjugate with Ru2+. Excess free biotin also displaces Ab-Ag complex from the solid phase, producing false elevations in sample analyte measurements.