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Clostridium Difficile GDH Reflex Toxin A/B by ELISA - Stool
Blood
Report in 12Hrs
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No Fasting Required
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Confirms presence of toxins A/B.
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Clostridium Difficile GDH Reflex Toxin A/B by ELISA - Stool
- Why is it done?
- Detects Clostridium difficile infection (CDI) by identifying glutamate dehydrogenase (GDH) antigen as an initial screening marker, followed by reflex testing for toxins A and B in positive samples, which are the pathogenic virulence factors responsible for disease
- Diagnose acute or chronic diarrhea in patients with recent antibiotic exposure, particularly following fluoroquinolones, cephalosporins, or clindamycin
- Evaluate patients with healthcare-associated diarrhea, hospital-acquired diarrhea, or symptoms consistent with pseudomembranous colitis
- Monitor for recurrent CDI in patients with history of C. difficile infection who present with new or worsening symptoms
- Performed during hospitalization or clinical evaluation when diarrheal symptoms develop, typically within days to weeks of antibiotic initiation
- Normal Range
- Negative Result: GDH antigen not detected; Toxin A/B not detected (when GDH positive). This is the normal or expected result indicating absence of C. difficile toxin-producing organisms
- Positive GDH/Negative Toxin: Indicates presence of C. difficile organism but no toxin production; considered colonization or asymptomatic carrier status; typically does not require treatment
- Positive GDH/Positive Toxin A and/or B: Confirmed active C. difficile infection (CDI) with toxin-producing strain; clinically significant finding requiring treatment
- Units of Measurement: Qualitative (positive/negative) or semi-quantitative optical density (OD) values depending on laboratory methodology
- Interpretation
- Two-Step Reflex Testing Algorithm: Initial screening uses GDH (glutamate dehydrogenase) ELISA to detect C. difficile antigen with high sensitivity (~95-99%); samples testing positive for GDH automatically reflex to toxin A/B testing, while negative GDH samples are reported as negative (no further testing)
- GDH Positive/Toxin Negative Interpretation: Represents asymptomatic colonization with non-toxigenic C. difficile strains or presence of toxigenic strains not currently producing toxins; typically <5% of GDH positive cases; generally does not require antimicrobial therapy unless clinically indicated
- GDH Positive/Toxin A and/or B Positive Interpretation: Definitive diagnosis of CDI; indicates toxin-producing C. difficile with toxin A, toxin B, or both present; correlates with clinical disease; warrants initiation of specific antimicrobial therapy
- Factors Affecting Results: Sample quality (inadequate or contaminated specimens may yield false negatives); timing of specimen collection relative to symptom onset; antibiotic therapy already initiated; intestinal transit time variations; presence of bile salts or other inhibitors in stool
- Clinical Significance: Positive toxin result guides antimicrobial selection (vancomycin or fidaxomicin based on severity); negative result in symptomatic patient suggests alternative diagnosis; repeat testing generally not recommended within 7 days due to continued toxin presence post-treatment; test of cure is not recommended for CDI
- Associated Organs
- Primary Organ System: Gastrointestinal tract, specifically the colon and large intestine; also affects overall intestinal microbiota and mucosal integrity
- Associated Conditions: Pseudomembranous colitis, antibiotic-associated diarrhea (AAD), healthcare-associated diarrhea (HCAD), fulminant colitis, toxic megacolon
- Diseases Diagnosed or Monitored: Clostridium difficile infection (initial episode), recurrent CDI, severe CDI, fulminant CDI with systemic toxicity
- Potential Complications of Abnormal Results: Severe dehydration and electrolyte imbalances; toxic megacolon with perforation risk; sepsis and septic shock; hemorrhage; acute kidney injury; extended hospitalization; increased mortality in elderly or immunocompromised patients; post-inflammatory irritable bowel syndrome; prolonged intestinal dysbiosis affecting subsequent antimicrobial susceptibility
- Follow-up Tests
- Additional Testing Based on Positive Results: Complete blood count (CBC) to assess for leukocytosis, anemia; comprehensive metabolic panel (CMP) for electrolyte abnormalities, renal function, liver involvement; procalcitonin or lactate to assess severity of infection and systemic inflammation
- Imaging and Procedural Investigations: Abdominal CT or KUB X-ray if severe disease, fulminant colitis, or toxic megacolon suspected; colonoscopy with biopsy for severe cases refractory to medical therapy or when diagnosis uncertain; consideration for surgical consultation if perforation or severe colitis present
- Monitoring and Follow-up Frequency: Clinical assessment during antimicrobial therapy; repeat stool testing NOT recommended within 7 days of positive result; test of cure NOT indicated for CDI; monitoring for recurrence in patients with risk factors for recurrent disease; follow-up laboratory studies (CMP, CBC) to assess response to treatment and resolution of inflammation
- Complementary Tests: Stool culture (if available) for antimicrobial susceptibility testing and strain identification; molecular testing (PCR) for toxin genes if confirmatory testing needed; ribotyping or whole genome sequencing for epidemiological investigation of outbreak situations
- Fasting Required?
- Fasting Requirement: No - fasting is not required for this stool-based test
- Patient Preparation Requirements: Collect fresh stool sample in sterile, leak-proof container; specimens should be collected during active diarrhea when toxin concentration is highest; submit sample within 2 hours of collection or refrigerate at 2-8°C if delayed transport is necessary; avoid contamination with urine or other materials
- Medications to Avoid: No medications need to be withheld; antimotility agents (loperamide, diphenoxylate) should generally be avoided as they may increase risk of complications and toxin production; antiperistaltic medications are contraindicated in suspected CDI
- Special Instructions: Minimize time between sample collection and laboratory receipt; samples should not be frozen unless absolutely necessary as toxins may degrade; notify laboratory of clinical suspicion for CDI; provide information about antibiotic exposure timing; sample collection ideally performed early in course of symptoms before treatment initiated for optimal sensitivity
How our test process works!
