Clostridium difficile


Indications for testing

  • Severe or persistent diarrhea in patients with risk factors (predominantly previous antibiotic use); may also occur several months after antibiotic use
  • Hospitalized patients with >72 hours diarrhea (or sooner with clinical indications)

Laboratory testing

  • CDC testing recommendations
  • Initial testing
    • CBC – often demonstrates leukocytosis; if leukocytosis not present, consider testing to rule out other organisms as the cause of diarrhea
    • Culture stool for Campylobacter, Salmonella, Shigella, E. coli (Shiga toxin-producing strains)
  • Testing for presence of toxins A and B on unformed stool (multiple repeats in 24-hour period are not recommended); should not be used to monitor therapy
    • Glutamate dehydrogenase enzyme immunoassay (EIA) – initial rapid test; does not identify toxin production (only presence of clostridium), and therefore, must be followed by toxin testing (so-called two-step test)
      • Sensitivity of the two-step test depends on EIA for toxin A
    • EIA for toxins – rapid but wide variability in sensitivity
    • PCR of stool for presence of toxin B gene
      • Emerging gold standard with high sensitivity and specificity
      • Rapid platforms available
    • Cytotoxin cell test – sensitive and specific; may require 48 hours for results
      • Performance based on transport time, pretreatment of patient
      • Fallen out of favor due to variable sensitivity and extended turnaround time
    • Stool culture for C. difficile with cytotoxin cell assay
      • Reference method
  • Endoscopy – classic exam effectively demonstrates pseudomembranous colitis but is invasive, and sensitivity is low (50%) for C. difficile-associated disease (CDAD)
  • Strain typing can be done for epidemiologic purposes using a variety of methods (eg, PCR ribotyping, pulsed field gel electrophoresis) but has no proven clinical utility and is not routinely performed by clinical laboratories

Differential Diagnosis

Clinical Background

Clostridium difficile causes 15-25% of all antibiotic-associated diarrhea (AAD) and >90% of antibiotic-associated pseudomembranous colitis (PMC).


  • Incidence – 336,000 C. difficile-related hospital stays documented in 2009, representing nearly 1% of all U.S. hospital stays (AHRQ, 2012)


  • Gram-positive, spore-forming rod
  • Obligate anaerobe
  • Produces toxins – A, B and binary
    • Toxin production is necessary to produce disease
    • A and B activate cytokines
    • Binary toxin (eg, ribotype 027 [B1/NAP1], ribotype 078 [ST-11])
      • Produced by hypervirulent strain
      • Tend to be drug resistant
  • Cultured in the stools of up to 50% of healthy neonates (<1 year), 3% of healthy adults, and 35% of hospitalized patients

Risk Factors

  • Antimicrobial administration within previous 60 days – >90% of cases have this risk factor
  • Age >65 years
  • Previous history of C. difficile disease
  • Prior or current hospitalization
  • Residence in long-term care center
  • Severe underlying illness

Clinical Presentation

  • Asymptomatic carrier state
  • Mild – non-bloody diarrhea (bacterial, parasitic, viral), abdominal cramping, >3 stools/day
  • Severe – abdominal pain, severe diarrhea, fulminant disease (toxic megacolon and paralytic ileus) with fever, anorexia, nausea and malaise
  • Recurrent disease (15-25% of patients) – typically occurs within 4 weeks of completion of therapy

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Clostridium difficile toxin B gene (tcdB) by PCR 2002838
Method: Qualitative Polymerase Chain Reaction

Use for rapid and clinically relevant diagnosis; test is highly sensitive

Follow-up test for positive results for GDH or other testing for toxin-producing strain

Clostridium difficile Cytotoxin Cell Assay 0060851
Method: Cell Culture/Neutralization

Use for clinically relevant diagnosis; test is the most specific and is highly sensitive

May take up to 48 hours to get results

Clostridium difficile Culture with Reflex to Cytotoxin Cell Assay 0060140
Method: Culture/Identification

Gold standard for C. difficile testing

If C. difficile culture is positive, then C. difficile cytotoxin cell assay is added

For routine stool screening, refer to Clostridium difficile toxin B gene (tcdB) by PCR

Culture alone does not distinguish toxin-producing strains

Requires up to 72 hours for report

Additional Tests Available
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Aid in determining cause of diarrhea; leukocytosis suggests bacterial etiology

Stool Culture and E. coli Shiga-like Toxin by EIA 0060134
Method: Culture/Identification

Rule out other organisms as cause of diarrhea

Routine stool culture includes culture for Salmonella, Shigella, Campylobacter, and E. coli 0157 as well as EIA for Shiga-like toxin from E. coli

Clostridium difficile Toxins (A & B) by EIA 0065146
Method: Qualitative Enzyme Immunoassay

Use for rapid and clinically relevant diagnosis; test is less sensitive than culture or cell assay

Follow-up test for positive results for GDH or other testing for toxin-producing strain

Not preferred initial test; use toxin B gene test instead

Do not use as stand-alone diagnostic test

Clostridium difficile Cytotoxin Antibody by Neutralization 2002552
Method: Antibody Neutralization

Research use only; not for initial diagnosis of C. difficile-associated diarrhea