A 2009 evaluation and comparison of a variety of commercially available toxin detection assays, glutamate dehydrogenase (GDH) assays, the cytotoxin assay, cytotoxigenic culture, and real-time PCR for the C. difficile tcdB gene revealed that ALL methods demonstrated a relatively low positive predictive value, which compromised the utility of a single test for laboratory diagnosis of C. difficile. However, PCR had the highest negative predictive value of all methods and was considered the optimum rapid single test.
Molecular methods for C. difficile are based on detecting the tcd gene. The patient sample used in testing is non-formed stool. With real-time methodology, results can be available within 2 to 3 hours. These methods are susceptible and demonstrate good sensitivity compared to all methods except toxigenic culture. As the methodologies and instrumentation are developed and improved, they are increasingly adaptable to the busy clinical diagnostic setting environment. The BD GeneOhm™, Meridian illumigene®, ROCHE cobas®, and Cepheid Xpert® assays are just a handful of examples using currently available molecular assays for C. difficile. The C. difficile molecular assays, developed by several manufacturers, may be run on molecular platforms of different sizes (large and small).
