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

Reporting Name

C. difficile Toxin PCR, F

Useful For

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

Clinical Information

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.


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.

Report Available

1 to 2 days

Day(s) Performed

Monday through Sunday

Clinical Reference

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

Method Name

Real-Time Polymerase Chain Reaction (PCR) using Fluorescent Resonance Energy Transfer (FRET)

Specimen Type


Ordering Guidance

This test is validated for formed feces, although testing formed feces for Clostridioides difficile is generally not clinically indicated.

Shipping Instructions

See Infectious Specimen Shipping Guidelines in Special Instructions for shipping information.

Necessary Information

Specimen source is required.

Specimen Required

The high sensitivity of amplification by polymerase chain reaction requires the specimen to be processed in an environment in which contamination of the specimen by Clostridioides difficile toxin DNA is unlikely.


Submit only 1 of the following specimens:



Specimen Type: Preserved feces

Supplies: Culture and Sensitivity Stool Transport Vial (T058))

Container/Tube: Commercially available transport system specific for recovery of enteric pathogens from fecal specimens (15 mL of nonnutritive transport medium containing phenol red as a pH indicator, either Cary-Blair or Para-Pak C and S)

Specimen Volume: Representative portion of feces; 5 mL

Collection Instructions:

1. Collect fresh fecal specimen and submit in container with transport medium.

2. Place feces in preservative within 2 hours of collection.

Specimen Stability Information: Ambient (preferred) <7 days/Refrigerated <7 days



Specimen Type: Unpreserved feces


Stool container, Small (Random), 4 oz Random (T288)

Stool Collection Kit, Random (T635)

Container/Tube: Fecal container

Specimen Volume: Representative portion of feces

Collection Instructions: Collect fresh fecal specimen and submit representative sample in fecal container.

Specimen Stability Information: Refrigerated (preferred) <7 days/Frozen <7 days

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Fecal Varies 7 days

Reference Values

Not applicable

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
CDFRP C. difficile Toxin PCR, F 54067-4


Result ID Test Result Name Result LOINC Value
SRC52 Specimen Source 31208-2
83124 Result 54067-4

Testing Algorithm

See Laboratory Testing for Infectious Causes of Diarrhea in Special Instructions.


If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

-Microbiology Test Request (T244)

-Gastroenterology and Hepatology Client Test Request (T728)

Mayo Clinic Laboratories | Microbiology and Infectious Disease Catalog Additional Information:

mml-giinfections, mml-idsurveillance