How Useful Is Repeat C difficile Testing?

John G. Bartlett, MD


March 11, 2009

Evaluation of Repeat

This retrospective study was designed to determine the potential value of repeat enzyme immunoassay (EIA) testing for Clostridium difficile, subsequent to multiple prior reports that have shown problems with sensitivity using this assay.

Cardona DM, Rand KH
J Clin Microbiol. 2008;46:3686-3689

Article Summary

This study was a retrospective review based on outcome of the Wampole C difficile Tox A/B II EIA performed from January 1 to December 31, 2006. During this time, investigators evaluated 8256 tests on 3112 patients; 49% of the tests had been repeated. For initially negative tests, the results with retesting at various intervals after the first negative test are shown in the Table .

These results indicate that only 0.9% of the repeat tests on the same day were positive. The yield increased to 1.8% to 3.8% at 2 days and subsequently increased to 10.6% on days 7 to 10.

The authors of this report concluded that, regardless of the sensitivity of a single EIA, repeat testing for C difficile toxin has a low yield.


These data are clinically relevant because many studies have shown the EIA, which is the test used for diagnosis of C difficile infection in about 95% of US hospitals, is relatively insensitive. The policy established by the analysis of these results at the University of Florida is to allow no more than 1 test every other day, or 48 hours apart. The researchers also pointed out that there was little point in repeating a positive test because specificity with this assay is excellent when done in the context of antibiotic-associated diarrhea. They also noted that since the institution of this policy, the number of tests per month has decreased by 50% at a cost savings of $40,000 per year.



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