Performance of TechLab C. DIFF QUIK CHEK™ and TechLab C. DIFFICILE TOX A/B II™ for the detection of Clostridium difficile in stool samples

Two membrane-bound enzyme immunoassays by TechLab, Blacksburg, VA, were evaluated and compared with the Triage® Micro C. difficile Panel (Biosite Diagnostics, San Diego, CA), with culture, and with cytotoxic assay. The TechLab panels were C. DIFF QUIK CHEK™ (QC-GDH) and C. DIFFICILE TOX A/B II™ (QC-toxinA/B), which detect glutamate dehydrogenase (GDH) and Clostridium difficile toxins A and B, respectively. The Triage Panel detects GDH (TR-GDH) and toxin A (TR-toxinA).MethodsStool samples were inoculated onto CCFA plates (Q-Labs, Quebec, Canada) after alcohol shock, and suspected colonies were identified by the MicroScreen C. difficile latex slide agglutination test (Microgen Bioproducts, Surrey, UK). TR-GDH, TR-toxinA, QC-GDH, and QC-toxinA/B tests were performed according to the manufacturers' instructions on all the samples. Samples positive for GDH or culture but negative for TR-toxinA and QC-toxinA/B were further tested by cytotoxin assay (CTA). CTA was also performed on samples that caused blackening of the Triage® Micro C. difficile Panel.ResultsA total of 313 of 401 stool samples were negative for GDH and toxins (78%). Eighty-eight samples were positive either for GDH or culture or both. Thirteen of these could not be evaluated for C. difficile-associated diarrhea (CDAD) because CTA test was not performed. Toxin/s was detected at least by one method in 46 (11.8%) of 388 samples that were positive for culture or GDH and were considered diagnostic of CDAD. The QC-GDH was more sensitive than culture and TR-GDH for the detection of C. difficile. However, in 18GDH-positive samples positive for either of the Triage or TechLab immunoassays, the culture remained negative. Ten (2%) results of the Triage immunoassays could not be evaluated because of discoloration of the panels. QC-GDH (93.5%) was more sensitive for detecting the presence of toxin-producing C. difficile than TR-GDH (79.5%). TR-toxinA was more specific for detecting the presence of toxin-producing C. difficile than QC-toxinA/B (100% and 96.9%, respectively).ConclusionsThe GDH tests had a faster turnaround time than the traditional culture methods. QC-GDH was most sensitive for the detection C. difficile-positive stools and was easy to use.