What diagnostic tools should be ordered for a patient presenting to the Emergency Room (ER) with symptoms of gastroenteritis?

Diagnostic Tools for Gastroenteritis in the Emergency Room

For patients presenting with symptoms of gastroenteritis in the emergency room, a comprehensive laboratory workup including complete blood count, inflammatory markers, electrolytes, liver function tests, and stool studies for infectious causes is essential, with IV contrast-enhanced CT scan recommended for suspected complications. 1

Initial Laboratory Evaluation

Essential Blood Tests

• Complete blood count (CBC) - to assess for anemia, leukocytosis (infection/inflammation), or thrombocytosis 1, 2
• Inflammatory markers:
  • C-reactive protein (CRP) - more sensitive for acute inflammation and correlates better with disease activity 1
  • Erythrocyte sedimentation rate (ESR) - useful for monitoring inflammation after the first 24 hours 1
• Metabolic panel:
  • Serum electrolytes - to assess for dehydration and electrolyte imbalances 1, 2
  • Liver enzymes - to evaluate for hepatic involvement 1, 2
  • Renal function tests - to assess kidney function and hydration status 1, 2
• Serum albumin - negative acute phase marker that decreases during inflammation 1, 2

Stool Studies

• Stool cultures - to identify bacterial pathogens 1, 3
• C. difficile toxin assay - especially important with recent antibiotic exposure 1, 4
• Multiplex PCR testing - preferred over traditional stool culture for faster results 3
• Fecal calprotectin - when available, helps distinguish inflammatory from non-inflammatory causes 1

Imaging Studies

First-Line Imaging

• IV contrast-enhanced computed tomography (CT) scan - recommended as the primary imaging modality in the emergency setting 1, 2
  • Detects complications such as intestinal perforation, strictures, bleeding, and abscesses
  • Guides decision-making for immediate surgery versus conservative management

Alternative Imaging Options

• Point-of-care ultrasonography - when CT is unavailable 1
  • Can assess for free intra-abdominal fluid, intestinal distension, or abscesses
  • Less sensitive but more readily available in some settings
• Magnetic resonance enterography (MRE) - if available 1, 2
  • Similar diagnostic accuracy to CT for assessing disease activity
  • Preferred for diagnosing strictures and differentiating fibrotic from inflammatory components
  • Reduces radiation exposure compared to CT

Endoscopic Evaluation

• Sigmoidoscopy - when available in the acute setting 1
  • Allows assessment of distal disease activity
  • Enables identification of bleeding sources
  • Permits biopsies for histological examination and CMV testing

Special Considerations

For Suspected Gastrointestinal Bleeding

• CT angiography - recommended for stable patients with signs of GI hemorrhage 1
  • Localizes bleeding site before potential angio-embolization or surgery
  • Particularly valuable when endoscopic assessment is unavailable

For Suspected Inflammatory Bowel Disease Complications

• Cross-sectional imaging (CT/MRI) - most sensitive and specific for detecting abscesses and stenosis 1
• For abscesses >3 cm - consider percutaneous drainage under radiological guidance 1, 2
• For abscesses <3 cm - may be treated with antibiotics alone with close monitoring 1, 2

Common Pitfalls to Avoid

1. Failing to test for C. difficile - particularly in patients with recent antibiotic exposure or healthcare facility contact 1, 4
2. Overlooking viral causes - viruses are the most common cause of gastroenteritis 3
3. Performing unnecessary tests in mild cases that are likely to resolve within a week 3
4. Delaying imaging in patients with severe symptoms or signs of complications 1
5. Missing CMV colitis in immunocompromised patients - requires specific testing 1

Algorithm for Diagnostic Approach

1. Assess severity:

   • Mild symptoms without red flags → basic labs only
   • Moderate to severe symptoms → comprehensive workup

2. For all patients:

   • CBC, CRP, ESR, electrolytes, liver enzymes, renal function, albumin
   • Stool studies for infectious causes

3. For patients with severe symptoms or suspected complications:

   • IV contrast-enhanced CT scan
   • Consider sigmoidoscopy if available

4. For patients with bleeding:

   • CT angiography if stable
   • Immediate surgical consultation if unstable

By following this systematic approach to diagnostic evaluation, clinicians can efficiently identify the cause of gastroenteritis and detect potential complications that may require urgent intervention.