Effective Monday, May 21, 2012, C. difficile testing on stool in the UIHC Microbiology Laboratory will be performed only once every 7 days for any one patient.  All C. difficile testing is now performed with the Xpert C. difficile/Epi PCR assay.  This assay is highly sensitive with a very high negative predictive value1.  Thus, testing multiple samples from consecutive days to rule out toxigenic C. difficile, as was common practice with toxin enzyme immunoassay (EIA) assays, is not recommended when using PCR.  It is also generally recommended that C. difficile PCR be performed only for patients with ≥3 liquid stools within a 24 hour period.  Further, only stool samples that take the shape of the container (i.e., are liquid and not formed) will be accepted for this testing.

Stool samples from previously negative patients received inside the 7 day window will automatically be rejected by the laboratory information system.  Also, please recall that repeat testing after a positive result will not be performed until after at least a 10 day period. “Tests of cure” are not recommended for management of C. difficile disease, as cure is defined as cessation of symptoms and the PCR can remain positive for long periods following treatment.

If you have any questions, please consult the Laboratory Services Handbook or contact Stacey Klutts, M.D., Ph.D., Medical Director of the Clinical Microbiology Laboratory, at 356-2990; Pager 1966.

1. Detection of toxigenic Clostridium difficile: comparison of the cell culture neutralization, Xpert C. difficile, Xpert C. difficile/Epi, and Illumigene C. difficile assays.  J Clin Microbiol. 2012 Apr;50(4):1331-5.