Molecular detection moves C. difficile testing forward

Download C.diff Infographic Traditional methods for identification of Clostridium difficile (C.difficile) include toxigenic culture, which is labor intensive and slow, and enzyme immunoassays (EIA), which have limited sensitivity. Algorithms have been developed using combinations of EIA testing to overcome shortcomings of individual assays.1 However, these algorithms may introduce delays in reporting results to physicians, which adversely impacts patient management. 

Molecular technologies (including nucleic acid amplification tests [NAAT]) offer better sensitivity and turnaround time in identifying toxigenic C. difficile when compared to several other approaches (glutamate dehydrogenase [GDH] assay, toxin A and B immunoassay, cell culture cytotoxicity neutralization assay), either alone or in combination.1 

In recent years, the frequency and severity of C. difficile-associated disease has continued to increase, prompting a need for rapid and reliable C. difficile testing, particularly in vulnerable elderly populations. By rapidly detecting C. difficile in patient stool samples, the cobas Cdiff Test* combines high assay sensitivity with rapid turnaround time and a minimum number of pre-analytic steps, to facilitate earlier intervention of patients suffering from C. difficile-associated disease.

The cobas Cdiff Test provides answers that help stop the threat of infection

The cobas Cdiff Test delivers sensitivity and specificity that Roche real-time polymerase chain reaction (PCR) can provide.

cobas cdiff test sensitivity and specificity

In a study of 682 samples, the cobas Cdiff Test demonstrated superior performance compared to direct culture cytotoxicity testing. 3

The performance that clinical confidence demands

The cobas Cdiff Test delivers sensitivity and specificity that Roche real-time polymerase chain reaction (PCR) can provide.

The cobas Cdiff Test: 

  • Selectively detects a specific C. difficile toxin gene directly from uniformed stool samples using real-time PCR technology
  • Detects a broad array of toxinotypes and ribotypes
  • Generates robust results automatically, using patented, state-of-the-art algorithms
  • Lower inhibition eliminates the need for repeat testing
  • Adds to the expanded test menu on the cobas® 4800 System, which also includes MRSA/SA testing

Provides confidence in results 

When compared to the combination of direct culture and enrichment culture, the cobas Cdiff Test demonstrated the following sensitivity, specificity, positive predictive values, and negative predictive values:

Combined Direct and Enrichment Culture 3
Sensitivity 92.9%
Specificity 98.7%
Positive Predictive Value 94.9%
Negative Predictive Value 98.2%

* Performance comparison in a study of 683 samples

Direct Culture* 3
Positive Percentage Agreement 97.3%
Negative Percentage Agreement 94.9%

Reduce hands-on time with a flexible, automated workflow

Accuracy delivered efficiently 

The cobas Cdiff Test requires only 3 simple steps for sample prep, minimizing sample handling. 3

cobas cdiff test sample preparation

Less hands-on time means more walk-away time 

The cobas Cdiff Test requires up to 70% less hands-on time than competitor platforms.

Total Hands-on Time2

Cdiff Hands-on Time

Run mixed batch assayscobas-4800-system-mixed-batch-testing-screen.png

The cobas 4800 System offers flexibility with parallel sample processing capabilities. cobas Cdiff Test samples can be run with different tests and sample types in one run. 

Run mixed batch assays of: 

  • Stool (cobas Cdiff Test) 
  • Nasal (cobas® MRSA/SA Test) 
  • Anogenital lesions (cobas® HSV 1 and 2 Test)
In addition to parallel sample processing, the cobas 4800 System offers an expanding test menu. 

cobas Cdiff Assay Performance and Specifications 3
Sample Type Unformed stool specimen
Sample Processing Simple handling, automated processing on the cobas 4800 System 
Target Region  C. difficile Toxin B (tcdB)
Contamination Control  AmpErase Enzyme
Internal Control Yes
Analytical Sensitivity  100% (31 toxinotypes detected) 
Analytical Specificity  100% (no cross reactivity across 98 bacteria, virus, fungi)
Clinical Sensitivity* 92.9%
Clinical Specificity*  98.7%
Limit of Detection  225 CFU/mL
Workflow  Mixed batch capability; optimized sample loading
*Compared with direct culture cytotoxicity test

Intended Use:
The cobas Cdiff Test on the cobas 4800 System is an automated, qualitative in vitro diagnostic test, that utilizes real-time polymerase chain reaction (PCR), for the direct detection of the toxin B (tcdB) gene of toxigenic Clostridium difficile in unformed (liquid or soft) stool specimens obtained from patients suspected of having C. difficile infection (CDI). The cobas Cdiff Test is intended for use as an aid in the diagnosis of CDI in humans in conjunction with clinical and epidemiological risk factors.



  1. Surawicz et al. Guidelines for diagnosis, treatment, and prevention of Clostridium difficile infections. Am J Gastroenterol. 2013 Apr;108(4):478-98.
  2. Argent Microbiology Workflow Study 2014. Roche data on file.
  3. cobas® Cdiff Test [package insert]. Indianapolis, IN: Roche Diagnostics; 2016.