Department of Pathology, Hennepin County Medical Center, Minneapolis, Minnesota, USA.
Division of Infectious Diseases, Department of Pathology and Laboratory Medicine, University of Minnesota, Minneapolis, Minnesota, USA.
J Clin Microbiol. 2019 Oct 23;57(11). doi: 10.1128/JCM.00719-19. Print 2019 Nov.
Laboratory tests for infection (CDI) rely on the detection of free toxin or molecular detection of toxin genes. The Singulex Clarity C. diff toxins A/B assay is a rapid, automated, and ultrasensitive assay that detects toxins A and B in stool. We compared CDI assays across two prospective multicenter studies to set a cutoff for the Clarity assay and to independently validate the performance compared with that of a cell culture cytotoxicity neutralization assay (CCCNA). The cutoff was set by two sites testing fresh samples from 897 subjects with suspected CDI and then validated at four sites testing fresh samples from 1,005 subjects with suspected CDI. CCCNA testing was performed at a centralized laboratory. Samples with discrepant results between the Clarity assay and CCCNA were retested with CCCNA when the Clarity result agreed with that of at least one comparator method; toxin enzyme immunoassays (EIA), glutamate dehydrogenase (GDH) detection, and PCR were performed on all samples. The cutoff for the Clarity assay was set at 12.0 pg/ml. Compared to results with CCCNA, the Clarity assay initially had 85.2% positive agreement and 92.4% negative agreement. However, when samples with discrepant results between the Clarity assay and CCCNA in the validation study were retested by CCCNA, 13/17 (76.5%) Clarity-negative but CCCNA-positive samples (Clarity/CCCNA) became CCCNA, and 5/26 (19.2%) Clarity/CCCNA samples became CCCNA, resulting in a 96.3% positive agreement and 93.0% negative agreement between Clarity and CCCNA results. The toxin EIA had 59.8% positive agreement with CCCNA. The Clarity assay was the most sensitive free-toxin immunoassay, capable of providing CDI diagnosis in a single-step solution. A different CCCNA result was reported for 42% of retested samples, increasing the positive agreement between Clarity and CCCNA from 85.2% to 96.3% and indicating the challenges of comparing free-toxin results to CCCNA results as a reference standard.
实验室检测感染（CDI）依赖于游离毒素的检测或毒素基因的分子检测。Singulex Clarity C. diff 毒素 A/B 检测是一种快速、自动化和超灵敏的检测方法，可检测粪便中的毒素 A 和 B。我们在两项前瞻性多中心研究中比较了 CDI 检测方法，为 Clarity 检测方法设定了一个截止值，并与细胞培养细胞毒性中和检测 (CCCNA) 进行了独立验证。该截止值由两个地点通过测试 897 名疑似 CDI 患者的新鲜样本确定，然后在四个地点通过测试 1005 名疑似 CDI 患者的新鲜样本进行验证。CCCNA 测试在一个集中的实验室进行。Clarity 检测方法与 CCCNA 检测结果不一致的样本，如果 Clarity 检测结果与至少一种比较方法一致，则用 CCCNA 重新检测；对所有样本进行毒素酶免疫检测（EIA）、谷氨酸脱氢酶（GDH）检测和 PCR。Clarity 检测方法的截止值设定为 12.0pg/ml。与 CCCNA 检测结果相比，Clarity 检测方法最初具有 85.2%的阳性符合率和 92.4%的阴性符合率。然而，当验证研究中 Clarity 检测方法与 CCCNA 检测结果不一致的样本用 CCCNA 重新检测时，17 个 Clarity 阴性但 CCCNA 阳性样本（Clarity/CCCNA）中有 13 个（76.5%）成为 CCCNA，26 个 Clarity/CCCNA 样本中有 5 个（19.2%）成为 CCCNA，导致 Clarity 和 CCCNA 结果之间的阳性符合率为 96.3%，阴性符合率为 93.0%。毒素 EIA 与 CCCNA 的阳性符合率为 59.8%。Clarity 检测方法是最敏感的游离毒素免疫检测方法，能够在一步解决方案中提供 CDI 诊断。42%的重新检测样本报告了不同的 CCCNA 结果，使 Clarity 与 CCCNA 的阳性符合率从 85.2%提高到 96.3%，表明比较游离毒素结果与 CCCNA 结果作为参考标准时存在挑战。
