What are the most sensitive stool assays for detecting Clostridium difficile (C diff) infection (CDI)?

Updated: Jul 25, 2019
  • Author: Faten N Aberra, MD, MSCE; Chief Editor: BS Anand, MD  more...
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The following are stool assays for C difficile, from the most sensitive to the least sensitive:

  • Stool culture is the most sensitive (sensitivity 90-100% and specificity 84-100%), but results are slow and may lead to delay in diagnosis if used alone

  • GDH EIA is very sensitive (sensitivity 85-100% and specificity 87-98%); this test detects the presence of GDH produced by C difficile; positive test results need to be rerun by another assay to verify

  • Real-time PCR assay may be used to detect C difficile gene toxin as an alternative “gold standard” to stool culture, with some studies demonstrating excellent sensitivity and specificity, as well as test-retest reliability [3, 44] ; in a study that used toxigenic culture as the gold standard, the sensitivity was 86%, the specificity was 97%, the positive predictive value (PPV) was 90%, and the negative predictive value (NPV) was 96%, for C difficile [3] (the PCR test is also inexpensive and has a fast turnaround time)

  • The stool cytotoxin test has a sensitivity of 70-100% and a specificity of 90-100%; the diarrheal stool is filtered and then added to cultured fibroblasts; a positive test result is the demonstration of a cytopathic effect that is neutralized by specific antiserum; however, this test result is reported only as positive or negative, it is expensive, and it requires overnight incubation and a tissue culture facility

  • EIA for detecting toxins A and B is used in most laboratories; it has moderate sensitivity (79-80%) but excellent specificity (98%); repeat testing is needed if the initial test is negative; EIA for toxin A is available, but it has come to be used less frequently because of the availability of EIA for toxins A and B

  • Latex agglutination technique can also be used to detect GDH; however, the sensitivity of this test is poor (48-59%), although the specificity is 95-96%

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