Repeated enzyme immunoassays have limited utility in diagnosing Clostridium difficile

Abstract

Many clinical laboratories use enzyme immunoassays (EIA) to diagnose Clostridium difficile-associated disease (CDAD). Clinicians frequently order three EIAs to "rule out" CDAD. We performed a retrospective cohort study to determine the clinical utility of repeating EIA testing to diagnose CDAD. We reviewed all EIAs performed by our laboratory during 2005, determined the total number of tests per patient and per testing episode, and calculated the relative negative predictive value (NPV) of one EIA compared to > or =2 EIAs. The laboratory performed 2,938 EIAs, of which 253 (8.6%) tests were positive. Most patients (85%) were diagnosed by the first EIA performed. Of >1,000 testing episodes that included > or =2 EIAs within 7 days, only 15 patients had a positive second or third test after negative initial testing. The relative NPV of the first EIA was 97.4%. These data suggest that using newer generation EIAs, repeated testing is of limited benefit in diagnosing CDAD.

European Society of Clinical Microbiology and Infectious Diseases (ESCMID): Data review and recommendations for diagnosing Clostridium difficile-infection (CDI)

“…and Drees et al. [55,56]. However, in an epidemic setting, NPVs of these tests will be significantly lower due to the higher prevalence of disease.…”

Overcoming barriers to effective recognition and diagnosis of Clostridium difficile infection

“…When a positive test result is obtained on initial testing, it can only be reported as provisionally positive, and further testing must be performed with, for example, a toxin detection test [1,11]. Another potential benefit of a two‐step approach to CDI diagnosis is that it discourages the submission of multiple faecal samples for repeat testing, which studies have shown can lead to a significant increase in the number of false‐positive test results, as well as being highly wasteful of resources [16,17].…”

Enzyme immunoassay for Clostridium Difficile Infection: Once, Twice or Thrice? Is the Falling Incidence of Clostridium Difficile an Artefact?

“…However, recent papers [7,[11][12][13][14][15][16] have suggested that repeat testing should be avoided. Drees et al [12] investigated the three sample rule using EIA testing. They reported that 85% of patients were diagnosed on the first test and attributed the improvement of the Aronnson et al results [20] to newer generation EIAs.…”

“…Thus, many clinicians order repeat stool sample testing following a negative result, in an attempt to increase the diagnostic yield. Frequently, up to three EIAs are ordered to 'rule out' CDI [12]. Previous guidelines did not specify the optimal number of tests in the diagnostic workup of CDI [11,13].…”

“…However, recent published data has questioned the merit of a policy of repeat stool testing for CDI [7,[11][12][13][14][15][16]. The latest guidance from the Department of Health state that EIAs alone are insufficient for the diagnosis of CDI [4].…”