Test Catalog

Test ID: CDFRP    
Clostridioides difficile Toxin, Molecular Detection, PCR, Feces

Useful For Suggests clinical disorders or settings where the test may be helpful

Rapid diagnosis of Clostridioides difficile-associated diarrhea (CDAD) and pseudomembranous colitis (PMC)

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Clostridioides difficile (formerly Clostridium difficile) is the cause of C difficile-associated diarrhea (CDAD), an antibiotic-associated diarrhea, and pseudomembranous colitis (PMC). In these disorders bacterial overgrowth of C difficile develops in the colon, typically as a consequence of antibiotic usage. Clindamycin and broad-spectrum cephalosporins have most frequently been associated with CDAD and PMC, but almost all antimicrobials may be responsible. Disease is related to production of toxin A and B. Treatment typically involves withdrawal of the associated antimicrobials and, if symptoms persist, orally administered and intraluminally active metronidazole, vancomycin, or fidaxomicin. Intravenous metronidazole may be used if an oral agent cannot be administered. In recent years, a more severe form of CDAD with increased morbidity and mortality has been recognized as being caused by an epidemic toxin-hyperproducing strain of C difficile (NAP1 strain). Many toxin-hyperproducing isolates also contain the binary toxin gene and are resistant to quinolones. This test does not differentiate between toxin-hyperproducing and nontoxin-hyperproducing strains.


Traditionally, diagnosis relied upon:

1. Clinical and epidemiologic features

2. Culture, which is labor intensive and time consuming

3. Cytotoxicity assays, which are also labor intensive and time consuming

4. Toxin detection immunoassays, which are insensitive

The described polymerase chain reaction assay detects the regulatory gene (tcdC) responsible for production of toxins A and B. This test is used for rapid diagnosis of CDAD and PMC enabling prompt treatment that may reduce hospital stays for inpatients with CDAD.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Not applicable

Interpretation Provides information to assist in interpretation of the test results

A positive polymerase chain reaction (PCR) result for the presence of the gene regulating toxin production (tcdC) indicates the presence of Clostridioides difficile and toxin A and/or B.


A negative result indicates the absence of detectable C difficile tcdC DNA, but does not rule-out C difficile infection and may occur due to inhibition of PCR, sequence variability underlying primers or probes, or the presence of C difficile DNA in quantities less than the limit of detection of the assay.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

The assay must be performed on fresh feces, fresh-frozen feces, or feces in transport medium.


The assay has not been validated as a test of cure. Since nucleic acid may persist after effective treatment, follow-up testing of a positive result is not recommended.


Interfering substances in the feces may affect the accuracy of the assay; results should always be interpreted in conjunction with clinical and epidemiologic findings.


Submission of more than one specimen for testing is not recommended.


Testing of colostomy, ileostomy, or colonoscopically collected specimens has not been validated.


Patients may asymptomatically carry Clostridioides difficile; clinical correlation is needed when deciding how to manage patients with a positive test result.


Repeat testing should not be performed on specimens collected less than 7 days apart.

Supportive Data

Results of the polymerase chain reaction (PCR) assay were compared with those of Clostridioides difficile toxin-detecting enzyme immunoassays (EIA) and culture of C difficile. Two hundred fecal specimens were studied in a blinded manner. C difficile was isolated from 49 specimens by culture and 44 of these were confirmed as containing 1 of the genes associated with toxin production (toxigenic culture). Using toxigenic culture as the "gold standard," the sensitivities and specificities, respectively, of the assays were 48% and 98% for the Premier Toxin A/B EIA (Meridian diagnostics); 48% and 99% for the ImmunoCard toxin A and B test (Meridian); 48% and 84% for the Xpect C difficile toxin A/B test (Remel); 32% and 100% for the Triage C difficile panel (for toxin A, Biosite Diagnostics); and 86% and 97% for the PCR assay. No cross-reactivity was observed in the PCR assay with a panel of 51 pathogens and normal flora, including other C species. The analytical sensitivity/limit of detection for the PCR assay was 35.8 cells/mcL in extracted fresh feces and 358 cells/mcL in extracted preserved feces.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Aichinger E, Schleck CD, Harmsen WS, Nyre LM, Patel R: Nonutility of repeat laboratory testing for detection of Clostridium difficile by use of PCR or enzyme immunoassay. J Clin Microbiol. 2008;46:3795-3797

2. Verdoorn BP, Orenstein R, Rosenblatt JE, et al: High prevalence of tcdC deletion-carrying Clostridium difficile and lack of association with disease severity. Diagn Microbiol Infect Dis. 2010;66:24-28

3. Karre T, Sloan L, Patel R, Mandrekar J, Rosenblatt J: Comparison of two commercial molecular assays to a laboratory-developed molecular assay for diagnosis of Clostridium difficile infection. J Clin Microbiol. 2011;49:725-727

4. Lawson PA, Citron DM, Tyrrell KL, Finegold SM: Reclassification of Clostridium difficile as Clostridioides difficile (Hall and O'Toole 1935) Prevot 1938. Anaerobe. 2016 Aug;40:95-99. doi: 10.1016/j.anaerobe.2016.06.008

5. Oren A, Garrity GM: List of new names and new combinations previously effectively, but not validly, published. Int J Syst Evol Microbiol. 2016 Sep;66:3761-3764. doi: 10.1099/ijsem.0.001321

Special Instructions Library of PDFs including pertinent information and forms related to the test