Injudicious use and questionable need of repeat stool ELISA (A/B) testing for the diagnosis of C. Difficile Associated Diarrhea (CDAD)

Background: There has been a significant increase in the prevalence, severity and mortality of CDAD, with an estimated 3 million new cases/year in US. Yet, the diagnosis of CDAD remains problematic. The most commonly used test is stool ELISA, but there are no clear guidelines for actual number of tests required for diagnosis, though common clinical practice presupposes three consecutive samples. Thus, we designed a study to assess physicians' ordering patterns and the diagnostic benefits of repeat second and third testing in the presence of a negative first sample.

Methods: A retrospective study of all hospitalized patients' stool ELISA (A/B), tested over 6 months (tests completed within 5 days of the first test were grouped into a single episode). Age, gender, length of stay, case mix index and results of stool ELISA were tabulated. Additionally, physicians' ordering patterns and proportion of positive stool tests relative to number of tests ordered was analyzed. A single positive ELISA result was interpreted as evidence for the clinical presence of CDAD.

Results: There was a total of 512 separate diarrhea episodes (total stool samples = 839) recorded on 343 patients, and only 112 (21.9%) of these episodes were positive for CDAD. Of positive patients, 72.3% were over 65, and 58.9% were female. Average length of stay was 31.2 days, with case mix index of 2.86. The most frequent ordering pattern was a single stool test (58.8%), followed by two tests (24.6%). Three tests were still ordered in 12.3% of cases. Of 112 positive cases, 103 (92%) were diagnosed on first test, 7 (6.3%) on second test and only 2 (1.8%) on third test.

Conclusion: This study highlights the injudicious use of stool ELISA (A/B) testing for diagnosis of CDAD and strongly suggests limiting the work up, only in those diarrhea patients who have known CDAD risk factors, to one single testing, while reserving a second repeat testing for the cases with high clinical suspicion, and avoiding the routine use of three consecutive sampling. Since C. Difficile is becoming an endemic health care problem throughout the US, resulting in a major financial burden for health care with an average cost of $48/test and an estimated overall cost of $144 million/year, it is imperative to develop clear guidelines for the use of stool ELISA (A/B) testing in the diagnostic work up of suspected CDAD so that physicians could practice evidence based medicine and become educated consumers.