Tweet
How Useful Is Repeat C difficile Testing?
Posted 03/11/2009
John G. Bartlett, MD
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.
Evaluation of Repeat Clostridium difficile Enzyme Immunoassay Testing
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.
Viewpoint
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.
-----------------------------------------------------------
Cardona DM, Rand KH.
Department of Pathology, Immunology, and Laboratory Medicine, P.O. Box 100275, University of Florida, College of Medicine, Gainesville, FL 32601-0275, USA.
Clostridium difficile is the leading cause of antibiotic-associated diarrhea and pseudomembranous colitis, which have significant morbidity and mortality. Accurate and timely diagnosis is critical.
Repeat enzyme immunoassay testing for C. difficile toxin has been recommended because of <100% sensitivity.
All C. difficile tests between 1 January 2006 and 31 December 2006 were retrospectively analyzed for results and testing patterns.
The Wampole C. difficile Tox A/B II enzyme immunoassay kit was used.
There were a total of 8,256 tests from 3,112 patients; 49% of tests were repeated.
Of the 3,749 initially negative patient tests, 96 were positive upon repeat testing within 10 days of the first test.
Of repeat tests, 0.9% repeated on day 0 (same day as the first test), 1.8% on day 1, 3.8% on day 2, 2.6% on day 3, 5.4% on days 4 to 6, and 10.6% on days 7 to 10 were positive.
Thirty-eight patients had a positive test within 48 h of an initial negative test, and based on chart review, 18 patients were treated empirically while 16 were treated following the new result.
None had evidence of medical complications.
Of initially positive patients, 91% were positive upon repeat testing on day 0, 75% on day 1, and 58% on day 2, to a low of 14% on days 7 to 10.
Depending on the clinical setting, these data support not repeating C. difficile tests within 2 days of a negative result and limiting repeat testing to >/=1 week of a positive result.
PMID: 18845820 [PubMed - indexed for MEDLINE]
Posted 03/11/2009
John G. Bartlett, MD
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.
Evaluation of Repeat Clostridium difficile Enzyme Immunoassay Testing
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.
Viewpoint
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.
-----------------------------------------------------------
Cardona DM, Rand KH.
Department of Pathology, Immunology, and Laboratory Medicine, P.O. Box 100275, University of Florida, College of Medicine, Gainesville, FL 32601-0275, USA.
Clostridium difficile is the leading cause of antibiotic-associated diarrhea and pseudomembranous colitis, which have significant morbidity and mortality. Accurate and timely diagnosis is critical.
Repeat enzyme immunoassay testing for C. difficile toxin has been recommended because of <100% sensitivity.
All C. difficile tests between 1 January 2006 and 31 December 2006 were retrospectively analyzed for results and testing patterns.
The Wampole C. difficile Tox A/B II enzyme immunoassay kit was used.
There were a total of 8,256 tests from 3,112 patients; 49% of tests were repeated.
Of the 3,749 initially negative patient tests, 96 were positive upon repeat testing within 10 days of the first test.
Of repeat tests, 0.9% repeated on day 0 (same day as the first test), 1.8% on day 1, 3.8% on day 2, 2.6% on day 3, 5.4% on days 4 to 6, and 10.6% on days 7 to 10 were positive.
Thirty-eight patients had a positive test within 48 h of an initial negative test, and based on chart review, 18 patients were treated empirically while 16 were treated following the new result.
None had evidence of medical complications.
Of initially positive patients, 91% were positive upon repeat testing on day 0, 75% on day 1, and 58% on day 2, to a low of 14% on days 7 to 10.
Depending on the clinical setting, these data support not repeating C. difficile tests within 2 days of a negative result and limiting repeat testing to >/=1 week of a positive result.
PMID: 18845820 [PubMed - indexed for MEDLINE]
