Laboratory Technical Bulletin
Topic: Clostridium difficile Toxin Gene Detection by DNA amplification
Test Name
Test Code
Method
Changes
Specimen
Test Schedule
C. difficile Toxin Gene
CDIFF
DNA Amplification
This assay replaces the Clostridium difficile Toxin A+B enzyme immunoassay test.
Formed stool specimens are not acceptable unless ileus is present.
Specimens collected within 7 days of a previous specimen will be rejected.
Raw stool or stool preserved in Cary-Blair-based transport medium. Transport
refrigerated (2-8 °C).
Monday through Sunday
Introduction: Because of their low sensitivity, enzyme immunoassay (EIA) tests are no longer recommended for
detection of C. difficile toxin in stool specimens.1 Recent reports indicate that molecular assays like the polymerase
chain reaction (PCR) provide sensitivities and specificities comparable to toxigenic culture, the current "gold
standard", and provide significantly shorter turnaround times.2 We compared the illumigene™ C. difficile
(Meridian Bioscience Inc., Cincinnati, OH) loop-mediated isothermal amplification (LAMP) technology with our
current EIA method (Premier™ Toxins A&B; Meridian Bioscience Inc., Cincinnati, OH) in order to evaluate the
LAMP assay for possible use in our laboratory. The LAMP assay detects the pathogenicity locus (PaLoc) found in
all toxigenic C. difficile strains. The EIA detects toxins A and B.
We tested 95 non-formed raw stool specimens from hospitalized patients by the EIA and LAMP methods.
Discrepant results were resolved by a PCR method that detects the tcdC regulatory gene. We obtained the
following results compared to PCR:
Test
Sensitivity Specificity
Current EIA test
64%
98%
New LAMP test
100%
100%
We concluded that the LAMP assay is superior to our current EIA method, provides similar TATs to the EIA, and
increases sensitivity and specificity.
Result Reporting: Results are reported as: Positive, Negative, or Inhibitory with recollection recommended.
References:
1.
Clinical Practice Guidelines for Clostridium difficile Infection in Adults: 2010 Update by the Society for Healthcare
Epidemiology of America (SHEA) and the Infectious Diseases Society of America (IDSA); Infection Control and Hospital
Epidemiology May 2010, vol. 31, no. 5
2.
Rapid and Sensitive Loop-Mediated Isothermal Amplification 1 (LAMP) Test for Clostridium difficile Diagnosis
Challenges Cytotoxin B Cell Test and Culture as Gold Standard ; Tnorén, * I Alriksson, Josefin Andersson, Thomas
Åkerlund, and Magnus Unemo . J. Clin. Microbiol. Vol. 49, No. 2 p. 710-711.
Additional Information: Contact Donald Piper, Chief Medical Technologist, Microbiology, NorDx, at (207) 396-7816 or by
email at piperd@mmc.org, or Monica Ianosi-Irimie, M.D., Ph.D., Laboratory Director, NorDx, at (207) 396-7809 or by email
at ianosm@mmc.org