Microbiology, Test Utilization

Clostridium difficile Two-Step Algorithm Testing

Spectrum Health Regional Laboratory is preparing to switch Clostridium difficile testing methods from solely using a molecular approach to a 2-step algorithm utilizing an Enzyme Immunoassay (EIA) that detects two C. difficile-specific proteins (glutamate dehydrogenase or GDH, and A/B toxin) with indeterminant EIA specimens reflexed to PCR (see flowchart below). It is estimated that approximately 90% of patients tested will be resolved by EIA and not require reflexive PCR testing. This algorithm decreases expenses to the patient by an average of 65% as compared to current testing without sacrificing result quality. Specimens will be batched for EIA testing at a frequency to ensure that results are available within 6 hours of receipt by the laboratory so that proper contact isolation precautions may be initiated when indicated.

Clinical Indications:

•   Patient has clinically significant diarrhea (3 or more liquid stools in the last 24 hours)1.
•   There has been no laxative use in the prior 24-48 hours or other explanation for diarrhea.

Clinical Contraindications:

•   Testing should not be performed as a “test of cure”1,2. A patient can have a positive result due to the presence of persistent toxin for an extended period of time after effective treatment. Repeat testing following treatment is not indicated since a positive result does not predict likelihood of recurrence or relapse.
•   In the absence of diarrhea, a positive test result represents asymptomatic colonization and not disease. The testing of asymptomatic patients is not indicated because treatment of positive results is not indicated.


•   Testing is only performed on watery stool specimens1,2. Formed stools received for testing will be rejected.

Ordering Considerations:

•    Repeat stool testing within a period of 7 days is unnecessary for the diagnosis of C. difficile disease3-5.
•    It is not necessary to order multiple C. difficile tests simultaneously to improve sensitivity.

1. Cohen SH, Gerding DN, Johnson S, et al. Clinical practice guidelines for Clostridium difficile infection in adults: 2010 update by the Society for Healthcare Epidemiology of America (SHEA) and the Infectious Diseases Society of America (IDSA). Infect Control Hosp Epidemiol 2010;31(5):431-55.
2. Dubberke ER, Gerding DN, Classen D, et al. Strategies to prevent clostridium difficile infections in acute care hospitals. Infect Control Hosp Epidemiol 2008;29 Suppl 1:S81-92.
3. Mohan SS, McDermott BP, Parchuri S, Cunha BA. Lack of value of repeat stool testing for Clostridium difficile toxin. The American journal of medicine 2006;119(4):356 e7-8
4. Drees M, Snydman DR, O’Sullivan CE. Repeated enzyme immunoassays have limited utility in diagnosing Clostridium difficile. Eur J Clin Microbiol Infect Dis 2008;27(5):397-9.
5. Aichinger E, Schleck CD, Harmsen WS, Nyre LM, Patel R. Nonutility of repeat laboratory testing for detection of Clostridium difficile by use of PCR or enzyme immunoassay. Journal of clinical microbiology 2008;46(11):3795-7.


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