Institute for Clinical Immunology and Transfusion Medicine, Justus Liebig University Giessen, Germany.
Thromb Res. 2011 Apr;127(4):345-8. doi: 10.1016/j.thromres.2010.12.001. Epub 2011 Jan 12.
The in vitro demonstration of antibodies against platelet factor-4/heparin (PF4/hep) complexes is an important contribution to the diagnosis of heparin-induced thrombocytopenia (HIT). The use of PF4/hep IgG-specific immunoassays enhances the specificity of HIT-investigations without any impairment of the sensitivity. Several IgG-specific immunoassays with different origin and structure of the target antigen-complex are commercially available.
Using a retrospective cohort consisting of 459 patients suspected to have HIT, we compared the performance characteristics of two commercially available IgG-specific immunoassays, GTI- (Genetic Testing Institute) and HIA-IgG-ELISA (Hyphen Biomed Research).
PF4/hep antibodies were detected in 85 and 81 sera using GTI- and HIA-IgG-ELISA, respectively. OD values and clinical likelihood of patients who tested positive in one assay only were significantly lower than in those who tested positive in both immunoassays. Both IgG-specific assays showed high negative predictive values (100%) and similar but unsatisfactory positive predictive values, determined by a minimum clinical score of 5 and a positive HIPA result (41% and 43%, respectively). The implementation of a confirmatory step using excessive heparin increased the PPV of both assays, but results in a reduction of NPV in HIA-IgG-ELISA.
The detection of IgG antibodies alone improves the clinical usefulness of immunoassays. However, functional assays remain indispensable to avoid the overdiagnosis of HIT caused by the detection of IgG non-platelet activating antibodies. The OD value in IgG immunoassays appears to correlate with the clinical relevance of the antibodies and might be used as a predictive parameter in the assessment of HIT.
体外检测针对血小板因子 4/肝素（PF4/hep）复合物的抗体是诊断肝素诱导的血小板减少症（HIT）的重要贡献。使用 PF4/hep IgG 特异性免疫测定法增强了 HIT 研究的特异性，而不会损害敏感性。有几种 IgG 特异性免疫测定法具有不同的来源和靶抗原复合物的结构，可在商业上获得。
使用由 459 例疑似患有 HIT 的患者组成的回顾性队列，我们比较了两种市售的 IgG 特异性免疫测定法，GTI-（遗传测试研究所）和 HIA-IgG-ELISA（Hyphen Biomed Research）的性能特征。
使用 GTI-和 HIA-IgG-ELISA 分别在 85 和 81 例血清中检测到 PF4/hep 抗体。仅在一种测定中检测为阳性的患者的 OD 值和临床可能性明显低于在两种免疫测定中均为阳性的患者。两种 IgG 特异性测定法均显示出高阴性预测值（100％）和相似但不理想的阳性预测值，通过最小临床评分 5 和阳性 HIPA 结果确定（分别为 41％和 43％）。通过使用过量肝素实施确认步骤，提高了两种测定法的阳性预测值，但会降低 HIA-IgG-ELISA 的阴性预测值。
单独检测 IgG 抗体可提高免疫测定法的临床实用性。然而，功能测定法仍然不可或缺，以避免因检测非血小板激活 IgG 抗体而导致的 HIT 过度诊断。在 IgG 免疫测定中，OD 值似乎与抗体的临床相关性相关，并且可以用作评估 HIT 的预测参数。
