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.

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

Method Name
A short description of the method used to perform the test

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

NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.


Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test

C. difficile Toxin PCR, F

Lists additional common names for a test, as an aid in searching

Antibiotic Associated Diarrhea

Antibiotic Associated Pseudomembraneous Colitis

C. difficile Toxin

C. difficile, Stool

Clostridium difficile, Feces

C. diff

C diff


C difficile Toxin

C difficile, Stool

Clostridioides difficile


Clostridium difficile, Stool

Clostridioides (Clostridium) difficile

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

Specimen Type
Describes the specimen type validated for testing


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
Defines the optimal specimen required to perform the test and the preferred volume to complete testing

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

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


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)

Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the Testing Laboratory

1 mL

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

Feces in gel transport medium
ECOFIX preservative
Formalin or polyvinyl acetate (PVA) fixative
Preserved feces received frozen

Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

Specimen Type Temperature Time Special Container
Fecal Varies 7 days

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

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.

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

Method Description
Describes how the test is performed and provides a method-specific reference

This method employs a target-specific detection system including polymerase chain reaction (PCR) primers, as well as fluorescent resonance energy transfer (FRET) hybridization probes targeting tcdC. The LightCycler instrument amplifies and monitors target nucleic acid sequences by fluorescence during PCR cycling. This is an automated PCR system that can rapidly detect amplified product development. The detection of amplified products is based on the FRET principle. For FRET product detection, a hybridization probe with a donor fluorophore, fluorescein, on the 3' end is excited by an external light source, which emits light that is absorbed by a second hybridization probe with an acceptor fluorophore, LC-Red 640, at the 5' end. The acceptor fluorophore then emits light of a different wavelength that is measured with a signal that is proportional to the amount of specific PCR product. The process is completed in a closed tube system.(Sloan LM, Duresko BJ, Gustafson DR, Rosenblatt JE: Comparison of real-time PCR for detection of the tcdC gene with four toxin immunoassays and culture in diagnosis of Clostridium difficile infection. J Clin Microbiol. 2008;46:1996-2001)

PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information


Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday through Sunday

Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

1 to 2 days

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

7 days

Performing Laboratory Location
Indicates the location of the laboratory that performs the test


Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.

  • Authorized users can sign in to Test Prices for detailed fee information.
  • Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
  • Prospective clients should contact their Regional Manager. For assistance, contact Customer Service.

Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.

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
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.

CPT codes are provided by the performing laboratory.


LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.

Test Id Test Order Name Order LOINC Value
CDFRP C. difficile Toxin PCR, F 54067-4
Result Id Test Result Name Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
SRC52 Specimen Source 31208-2
83124 Result 54067-4

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports