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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Clostridium difficile toxin B PCR, NAP1 if positive


CPT Code(s): 87493; if indicated, add CPT 87493 for NAP1 reflex testing

Methodology: PCR

Clinical Significance: Detects Clostridium difficile toxin B (tcdB) and if positive detects binary toxin and tcdC deletion of hypervirulent, epidemic 027/NAP1/B1 strain in stool.

Days Performed: Daily.

Turnaround Time: Stat: Not available stat.
Routine: 4 hours.

Specimen Requirements

Specimen: Liquid or unformed stool. No swabs.

Collection Container: Preferred: Sterile container

Collection Volume: Preferred: 2 mL
Pediatrics: 2 mL

Sample Analyzed: Liquid or unformed stool

Specimen Transport: Transport specimen to UWHC Microbiology Laboratory (B4/231) within 24 hours of collection; refrigerate if delay.

Unacceptable Criteria: LIMIT: One specimen every 7 days. Formed stool is unacceptable.
Test of cure samples should not be submitted. Cure should be based on clinical response to therapy.

Stability: Ambient: 24 hours
Refrigerated: 5 days
Frozen: Not acceptable


Expected Results:


Test Limitations:

Potential interfering substances are Vagisil™ cream and zinc oxide paste.


Results of this assay are not affected by blood, barium sulfate, metronidazole, or vancomycin present in stool specimens.

Additional Information:

Testing not available 9pm to 7am.


Reserve testing for patients with 3 or more unformed stools in 1 or more days.


Negative predictive value is greater than 97%.


Positive tests occur in patients colonized by C. difficile without colitis. Reserve treatment for those with clinical colitis.


Performance characteristics have not been established for patients under the age of two.  Positive test results for C. difficile do not correlate well with disease in patients <2 years old.  Interpret tests on those under the age of two with caution.


C. difficile positive patients should be placed in enhanced contact precautions for the duration of hospitalization.


The C. difficile epidemic strain, described here as NAP1, is toxinotype III and has been associated with worse disease severity, i.e., it is hypervirulent.  The epidemic strain of C. difficile is REA (restriction endonuclease) group BI, pulse field gel electrophoresis (PFGE) type NAP1, and PCR robitype 027.  The strain also contains an 18 bp tcdC deletion and produces binary toxin.  The assay used to test this specimen detects the tcdC deletion and the binary toxin.  Because the assay does not use REA, PFGE or PCR ribotyping for detection of 027/NAP1/BI, results are considered presumptive.


Non-027/NAP1/BI isolates representing toxinotype XIV and occasionally toxinotypes IV, V and X may be reported as NAP1 positive using this assay.

Clostridium C difficile C diff  Cdiff CDPCR NAP1

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