Cross Reactivity Using Antigen Assays

Although it is theoretically possible to perform a solid-phase EIA to assess cross-reactivity (Amiral et al., 1995), this is complicated because the antigen has to be coated as a complex to the solid phase. This problem has been overcome in a fluid-phase EIA described by Newman and colleagues (1998). Because this assay detects binding to a defined quantity of labeled PF4-containing antigen, the assay is able to determine in vitro cross-reactivity more accurately than the solid-phase EIA. These investigators observed an in vitro cross-reactivity rate of 88% for LMWH; about half the HIT samples reacted weakly against danaparoid in their study. The fluid-phase EIA has also been used to show that the antithrombin-binding pentasaccharide, fondaparinux, does not cross-react with HIT-IgG antibodies (Warkentin et al., 2005b).

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