Table 5.

Clinical decision support for interpretation of Clostridium difficile EIA results

Result Combination	Interpretation and Comment
Antigen positive, toxin positive	Interpretation: Positive for toxigenic C difficile. Comment: These results are consistent with C difficile infection. Detection of both antigen and toxin are expected when C difficile infection is present.
Antigen positive, toxin negative	Interpretation: C difficile present but toxin not detected. Comment: This pattern is most consistent with C difficile colonization (occurs in 20% of hospitalized patients). There is no indication to treat C difficile colonization and anti–C difficile antibiotics do not prevent subsequent infection. Antimicrobial therapy and proton pump inhibitors should be avoided. Consideration should be given to medication causes of diarrhea, such as laxatives, stool softeners, colchicine, metformin, HIV protease inhibitors, antibiotics, or certain chemotherapy agents, among others. Enteral feeds are also a common cause of diarrhea. If symptoms and signs are consistent with colitis and risk factors are present for C difficile (eg, recent antibiotic exposure), additional testing using C difficile PCR may be performed, but testing requires prior authorization by the AS team.
Antigen negative, toxin positive	Interpretation: Undetermined. Comment: Toxin positivity should not occur without antigen positivity. Consider repeat testing if clinically indicated.
Antigen negative, toxin negative	Interpretation: Negative for toxigenic C difficile. Comment: There is no evidence of C difficile infection. Consider other causes of diarrhea. Consideration should be given to medication causes of diarrhea, such as laxatives, stool softeners, colchicine, metformin, HIV protease inhibitors, antibiotics, or certain chemotherapy agents, among others. Enteral feeds are also a common cause of diarrhea.

Abbreviation: HIV, human immunodeficiency virus.