Case 10: Diagnostic Testing

Here are the initial lab results:

Stool testing reveals the following: 

Polymerase chain reaction (PCR) for Clostridium difficile:  Positive
Enzyme immunoassay for Clostridium difficile toxin:  Positive

How would you interpret these tests?
Active Clostridium difficile infection
The ACG and IDSA guidelines recommend a two-step algorithm for the diagnosis of Clostridium difficile (C difficile) diarrhea. PCR tests detect the presence of the gene encoding toxin, confirming the presence of a toxigenic strain. They cannot confirm if toxin is being produced infected individuals. Glutamate dehydrogenase (GDH) is an enzyme produced in large amounts by both toxigenic and nontoxigenic strains of C. difficile and other clostridial species. The test detecting GDH antigen is extremely sensitive and functions well as a screening tool, with a high negative predictive value. Hence GDH based tests must be confirmed by a PCR test. Eventually, both of the above tests should be followed by an enzyme immunoassay (EIA) to detect the presence of toxin A and B which then confirms active C. difficile infection.
Colonization with Clostridium difficile
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Presence of non-toxigenic strains of Clostridium difficile
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Diagnostic imaging:
Given the abdominal pain, a CT Abdomen and Pelvis with intravenous contrast was obtained for our patient.


CT was notable for diffuse, moderate to severe wall thickening of the colon with moderate distention of the transverse colon measuring up to 6.69 cm.

Patient was diagnosed with C. diff diarrhea. How would you classify the severity of infection?
Mild to Moderate
As per IDSA and SHEA classification, mild to moderate disease is defined as WBC <15,000 cells/mm3 and serum creatinine <1.5 times the premorbid levels.
While our patient does meet features of severity, he has additional concerning features as well. As per ACG classification, infections are considered severe if serum albumin <3g/dl, WBC count >15,000 and abdominal tenderness is present on exam. IDSA and SHEA define severe infections as WBC >15,000 cells/mm3 and serum creatinine >1.5 times the premorbid levels
Severe and Complicated / Fulminant
Given the added features of hypotension, megacolon and serum lactate >2.2 mmol/l, this patient’s infection would be defined as severe and complicated.

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