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‘Ultrasensitive’ C. difficile assay outperforms current testing options
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Singulex’s Clarity C. diff toxins A/B assay could potentially be used as a standalone test for patients with Clostridium difficile infection, according to findings presented at the European Congress of Clinical Microbiology and Infectious Diseases.
As previously reported in pilot studies, when used in conjunction with the Singulex Clarity system, the Singulex assay can detect toxins rapidly and at 100 times lower concentrations than current immunoassays.
In a more recent analysis, Niaz Banaei, MD, associate professor in the department of pathology at Stanford University School of Medicine, and colleagues evaluated the performance of the test on stool samples from 311 patients with potential C. difficile infection (CDI). All samples had been previously tested by PCR (Xpert C. difficile, Cepheid). PCR-positive samples (n = 211) were tested again for free toxins with a rapid membrane enzyme immunoassay, or EIA (C. diff Quik Chek Complete, Techlab). EIA-negative samples (n = 110) were further tested with a cell cytotoxity neutralization assay (CCNA). Of the 110 EIA-negative samples, 31 were found to be positive with CCNA and 79 were negative, according to the study. Samples were considered CDI-negative if PCR was negative, and samples that were positive with EIA or CCNA were considered true-toxin positive.
The stool samples were then tested with the Singulex assay to compare its sensitivity and specificity against current testing options. Of the 132 samples that were positive with PCR, EIA and CCNA, 129 were found to be positive by the Singulex assay, and all PCR-negative samples were similarly found to be negative with the Singulex assay, resulting in 97.7% sensitivity and 100% specificity. The assay also detected toxins in 23% of samples that were positive with PCR but negative with EIA and CCNA. Altogether, the Singulex Clarity C. diff toxin A/B assay may lead to a more precise selection of patients who need treatment, according to the study results.
Two additional studies presented at ECCMID also supported the use of the Singulex assay. One study, which evaluated the analytical performance of the test, showed that it detected C. difficile toxins at concentrations lower than other commercially available toxin assays and had high sensitivity and specificity compared with CCNA. In the other study, which evaluated the clinical performance of the Singulex assay, it outperformed PCR, EIA and two multistep algorithms.
The company expects FDA registration for Singulex Clarity C. diff toxin A/B assay before the end of 2018.
“Most labs are currently using sensitive but not very specific C. difficile testing algorithms. This is understandable because no one wants to miss any cases of C. difficile infection,” Banaei told Infectious Disease News. “The Singulex Clarity C. diff toxins A/B assay offers both sensitive and specific C. difficile testing, eliminating the problem laboratories currently have with specificity.” – by Marley Ghizzone
References:
Banaei N, et al. Abstract P2281. Presented at: European Congress of Clinical Microbiology and Infectious Diseases; April 21-24, 2018; Madrid.
Bartolome A, et al. Abstract P2282. Presented at: European Congress of Clinical Microbiology and Infectious Diseases; April 21-24, 2018; Madrid.
Young S, et al. Abstract P2283. Presented at: European Congress of Clinical Microbiology and Infectious Diseases; April 21-24, 2018; Madrid.
Disclosures: Banaei reports research funding through a contract to Stanford University from Singulex and serves on their medical advisory board.