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HelpTest Code CDNAT C difficile Toxin,Nucleic Acid/with reflex
Useful For
Specimens that test positive for Clostridioides difficile Nucleic Acid Test will automatically reflex to GDH and toxin A/B Enzyme Immunoassay (EIA).
Clostridioides difficile is the leading infectious cause of nosocomial (hospital-acquired) acute diarrhea and significantly contributes to the overall number of nosocomial diarrhea cases. It is recommended that all hospitalized patients over the age of two who present with acute diarrhea?especially those with a new onset of more than three unformed stools within a 24-hour period and a recent history of antibiotic use?undergo testing for C. difficile.
The possibility of asymptomatic colonization by both toxigenic and nontoxigenic strains of C. difficile complicates the diagnosis, and improper testing can result in overdiagnosis. A multistep approach to laboratory testing is recommended for diagnosing C. difficile infection.
This diagnostic process follows a two-step algorithm. The first step involves a PCR test for C. difficile Toxin B. If the result is positive, it is automatically followed by an enzyme immunoassay that detects the C. difficile antigen, glutamate dehydrogenase (GDH), as well as toxins A and B.
This assay should only be used to test patients exhibiting signs and symptoms of a toxigenic C. difficile infection; it should not be used to screen asymptomatic individuals. According to the 2017 IDSA and SHEA guidelines, no more than one specimen should be submitted within a 7-day period during the same episode of diarrhea.
Testing stool samples for C. difficile in patients under 2 years of age is not recommended, as there is a high rate of asymptomatic carriage of toxigenic C. difficile in this age group. A positive test for the C. difficile toxin gene in infants does not definitively indicate C. difficile disease; it is important to investigate other potential causes of diarrhea. (Clinical Practice Guidelines for Clostridium difficile Infection in Adults and Children: 2017 Update by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA), Clinical Infectious Diseases, Volume 66, Issue 7, 1 April 2018, Pages e1?e48).
Additionally, C. difficile can also cause community-associated diarrhea in outpatient settings. For more information, please refer to the Guidelinesfor Diarrheal Pathogen Testing
Synonyms/Keywords
C. difficile Toxin PCR, Clostridioides difficile Toxins A and B, CTOX, C diff, CDNAT
Specimen Requirements
| Fasting Required | Specimen Type | Preferred Container/Tube | Acceptable Container/Tube | Specimen Volume | Specimen Minimum Volume (allows for 1 repeat) |
Pediatric Minimum Volume (no repeat) |
|---|---|---|---|---|---|---|
| No | Feces | Leak-proof container | 2.0 mL | 1.0 mL | 100 uL |
Collection/Processing Instructions
Fresh, unpreserved, unformed (i.e. takes the shape of the container at room temperature) feces in leak-proof container.
For more information on Specimen Collection Media/Swab, see Specimen Transport Pictorial.
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Feces | Refrigerated | < 48 hours |
Rejection Criteria
| Formed fecal specimens |
|---|
| More than one specimen within 7 days |
| Specimens >48 hours old |
| Specimens that are stored or transported frozen |
| Specimens transported in Cary-Blair or C & S transport medium |
| Stool collected on wooden tongue depressor |
| Specimens contaminated with urine |
| Samples collected from patients <2 years of age |
Test Information
Clostridiodes difficile infection is a toxin-mediated disease and the majority of C. diff strains produce two toxins including Toxin A, an enterotoxin, and Toxin B, a cytotoxin; however, strains have been isolated that are Toxin A-/B+. Toxin A+/B- strains have been reported but the incidence of these variants appears to be extremely rare. Although both Toxin A+/B+ and Toxin A-/B+ strains circulate in the population, strains that are Toxin A+/B+ are currently dominant.
Interpretive comments will generate based on C. difficile Nucleic Amplified test, GDH and toxin A/B combinations based on testing results.
| PCR | GDH | Toxin A/B | Comment |
| Positive | Positive | Positive | Positive for Clostridioides difficile infection (CDI). |
| Positive | Positive | Negative | A PCR-Positive sample that is GDH-positive and toxin A/B negative by enzyme immunoassay (EIA) may indicate true Clostridioides difficile infection (CDI). Correlation with clinical symptoms is advised. |
| Positive | Negative | Negative | A PCR-Positive sample with no GDH or toxin A/B detected by enzyme immunoassay (EIA) may indicate colonization. However, if clinical symptoms are consistent with Clostridioides difficile infection (CDI), treat according to guidelines. |
| Negative | N/A | N/A | Negative for Clostridioides difficile infection (CDI). |
Reference Range Information
All Performing Sites: Negative
Marshfield Labs Performing Department
Marshfield Labs Molecular Pathology
Performing Information
| Performing Location | Day(s) Test Performed | Analytical Time | Methodology/Instrumentation |
|---|---|---|---|
| Marshfield | Monday through Sunday | 24 hours | Nucleic Acid Test (PCR based) |
CPT Codes
| CPT | Modifier (if needed) |
Quantity | Description | Comments |
|---|---|---|---|---|
| 87493 | Infectious agent antigen detection test by PCR test |
|
||
| 87449 | GDH antigen detection | As needed |
||
| 87324 | Detection of C. difficile toxin | As needed |
Outreach CPT Codes
| CPT | Modifier (if needed) |
Quantity | Description | Comments |
|---|---|---|---|---|
| 87493 | Infectious agent antigen detection test by PCR test |
|
||
| 87449 | GDH antigen detection | As needed | ||
| 87324 | Detection of C. difficile toxin | As needed |
Ordering Applications
| Ordering Application | Description |
|---|---|
| Cerner | Clostridium difficle Toxin, NAT (CDNAT) |