Eriksson Susann, Ilva Tuomo, Becker Charlotte, Lund Juha, Porela Pekka, Pulkki Kari, Voipio-Pulkki Liisa-Maria, Pettersson Kim
Department of Biotechnology, University of Turku, Turku, Finland.
Clin Chem. 2005 May;51(5):848-55. doi: 10.1373/clinchem.2004.040089. Epub 2005 Feb 17.
We recently provided evidence that circulating autoantibodies against cardiac troponin I (cTnI) or the troponin complex cause negative interference in cTnI immunoassays. By comparing three cTnI immunoassays, we further explored the phenomenon of circulating autoantibodies and their consequences in patient samples.
We developed a cTnI immunoassay with a novel assay design using three antibodies, two of which bind epitopes outside the stable, central part of cTnI. Samples from 541 chest pain patients were measured with the new cTnI assay and with a first-generation cTnI assay (Innotrac Aio cTnI) using a conventional midfragment assay design. Using another sample cohort, we also compared the new assay with a second-generation cTnI assay (Access AccuTnI).
The analytical detection limit of the new cTnI assay was 0.012 microg/L, and the lowest concentration giving a total imprecision (CV) of 10% was 0.060 microg/L. The mean difference (95% limits of agreement) between the new cTnI and Aio cTnI assays was larger in admission samples (21.0%; -107.8% to 149.7%) than in samples taken 6-12 h (12.8%; -61.5% to 87.2%) and 24 h after admission (3.0%; -71.3% to 77.4%; P <0.001). With the lowest concentrations giving 10% CV (0.22 microg/L for Aio cTnI) used as cutoffs, 14.3% (n = 76) of admission samples were positive only with the new assay, whereas 13.5% (n = 72) were positive with both assays. Of samples taken at 6-12 and 24 h, 10.2% (n = 31) and 8.3% (n = 29) were positive only with the new assay. ROC curve analysis of admission samples showed a significantly higher area under the curve for the new cTnI assay (0.940) than for the Aio cTnI assay (0.846; P <0.001). The new cTnI assay gave generally lower results than the AccuTnI assay; the mean (95% limits of agreement) differences were -58.9% (-151.8% to 34.0%) in admission samples. In samples with severe interference from autoantibodies, median ratios between the new assay and AccuTnI were higher than in samples with no apparent troponin autoantibodies (0.875 vs 0.481; P<0.001).
The new cTnI assay, which is based on a novel antibody combination different from the conventional midfragment antibody approach, offers improved detection of cTnI in samples containing troponin autoantibodies.
我们最近提供的证据表明，循环抗心肌肌钙蛋白I（cTnI）自身抗体或肌钙蛋白复合物会对cTnI免疫测定产生负干扰。通过比较三种cTnI免疫测定方法，我们进一步探讨了循环自身抗体现象及其在患者样本中的影响。
我们开发了一种采用新型测定设计的cTnI免疫测定方法，使用三种抗体，其中两种抗体结合cTnI稳定中心部分之外的表位。采用新型cTnI测定方法和采用传统中段片段测定设计的第一代cTnI测定方法（Innotrac Aio cTnI）对541例胸痛患者的样本进行检测。使用另一组样本队列，我们还将新型测定方法与第二代cTnI测定方法（Access AccuTnI）进行了比较。
新型cTnI测定方法的分析检测限为0.012μg/L，总不精密度（CV）为10%时的最低浓度为0.060μg/L。新型cTnI测定方法与Aio cTnI测定方法之间的平均差异（95%一致性界限）在入院样本中（21.0%；-107.8%至149.7%）大于入院后6 - 12小时样本中（12.8%；-61.5%至87.2%）和入院后24小时样本中（3.0%；-71.3%至77.4%；P<0.001）。以总不精密度为10%时的最低浓度（Aio cTnI为0.22μg/L）作为临界值，14.3%（n = 76）的入院样本仅在新型测定方法中呈阳性，而13.5%（n = 72）的样本在两种测定方法中均呈阳性。在入院后6 - 12小时和24小时采集的样本中，分别有10.2%（n = 31）和8.3%（n = 29）仅在新型测定方法中呈阳性。入院样本的ROC曲线分析显示，新型cTnI测定方法的曲线下面积（0.940）显著高于Aio cTnI测定方法（0.846；P<0.001）。新型cTnI测定方法的结果通常低于AccuTnI测定方法；入院样本中的平均差异（95%一致性界限）为-58.9%（-151.8%至34.0%）。在受到自身抗体严重干扰的样本中，新型测定方法与AccuTnI的中位数比值高于无明显肌钙蛋白自身抗体的样本（0.87vs0.481；P<0.001）。
基于与传统中段片段抗体方法不同的新型抗体组合的新型cTnI测定方法，在检测含有肌钙蛋白自身抗体的样本中的cTnI时具有更好的性能。
