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UFH Clinical HIT

FIGURE 2 Ratio of antibody binding to PF4/polysaccharide complexes compared to PF4 alone by fluid-phase EIA. Results of fluid-phase EIA testing for sera from 15 patients who formed anti-PF4/ heparin IgG antibodies (detected using solid-phase EIA) while receiving enoxaparin (n = 6, closed circles) or fondaparinux (n = 9, open circles). The data are expressed as ratios of binding to PF4 in the presence of polysaccharide (UFH, 0.6 IU/mL, LMWH 0.5 anti-Xa U/mL, danaparoid 0.1 anti-Xa U/mL, and fondaparinux, 0.1, 0.4, 1.2, and 10.0 mg/mL) over the baseline (buffer). Horizontal bars indicate medians. Asterisks indicate the four samples that tested positive (in the presence of UFH) in the platelet activation assay. For comparison, results are also shown for 15 patients with clinical HIT. Statistically significant increases in reactivity (null hypothesis, mean ratio of OD [presence of drug]/OD [presence of buffer] = 1) for the 15 sera obtained from patients in the orthopedic trials were observed for UFH (p = 0.0032), LMWH (p = 0.0004), danaparoid (p = 0.0016), but not with fondaparinux at any concentration (p>0.05). Whereas 14 of 15 sera from patients in the orthopedic trials exhibited more than twofold greater reactivity than baseline against PF4/LMWH, none reacted similarly against PF4/fondaparinux (p = 0.0002 by McNemar's test, two-tailed). Abbreviations: EIA, enzyme-linked immunoassay; HIT, heparin-induced thrombocytopenia; LMWH, low molecular weight heparin; UFH, unfractionated heparin. Source: From Warkentin etal., 2005.

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