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, of all methods, PCR had the highest negative predictive value, and was considered the optimum rapid single test.
Molecular methods for C. difficile are based on the detection of the tcd gene. With the application of real time methodology, results can be available within 2 to 3 hours. These methods are highly sensitive and demonstrate good sensitivity, in comparison to all methods with the exception of toxigenic culture. As the methodologies and instrumentation are developed and improved, they are increasingly adaptable to the environment of a busy clinical diagnostic setting. The BD GeneOhm™ and Meridian illumigene® assays are examples of currently available molecular assays for C. difficile.