What initial tests should be done in the Emergency Department (ED) setting for a patient presenting with diffuse abdominal pain, vomiting, and loose stools?

Initial Tests for Patients with Diffuse Abdominal Pain, Vomiting, and Loose Stools in the ED

In the Emergency Department setting, patients presenting with diffuse abdominal pain, vomiting, and loose stools should undergo laboratory testing including complete blood count, C-reactive protein, electrolytes, liver enzymes, renal function, serum albumin, and stool studies, along with abdominal CT scan with IV contrast as the primary imaging modality. 1

Laboratory Tests

Essential Initial Laboratory Panel:

• Complete blood count (CBC) - to assess for leukocytosis, anemia, thrombocytosis 1, 2
• C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) - inflammatory markers 1, 3
• Comprehensive metabolic panel:
  • Electrolytes - to identify dehydration and electrolyte imbalances 1
  • Liver enzymes - to evaluate hepatobiliary involvement 1, 2
  • Renal function tests - to assess kidney function and dehydration 1, 2
• Serum albumin and pre-albumin - to assess nutritional status and degree of inflammation 1
• Lipase - to evaluate for pancreatitis 2

Stool Studies:

• Stool cultures - to rule out infectious causes 1, 3
• Clostridioides difficile toxin test - especially important in patients with recent antibiotic use 1, 3
• Fecal calprotectin - when available, helps differentiate inflammatory from non-inflammatory causes 3

Imaging Studies

First-line Imaging:

• CT scan of abdomen and pelvis with IV contrast - highest sensitivity and specificity for detecting abscesses, obstruction, perforation, and inflammatory conditions 1
  • Does not typically require oral contrast in acute settings 1
  • Provides comprehensive assessment of multiple organ systems 1

Alternative/Adjunctive Imaging:

• Abdominal ultrasound - useful screening tool when CT is unavailable, particularly valuable for right upper quadrant pathology 1
• Plain abdominal X-ray - limited utility but may show obstruction, perforation (free air), or ileus 1

Clinical Decision Algorithm

1. Assess hemodynamic stability:

   • If unstable: Immediate resuscitation measures before proceeding

2. Order initial laboratory tests:

   • CBC, CRP/ESR, electrolytes, liver enzymes, renal function, serum albumin, lipase
   • Stool studies (cultures, C. difficile toxin)

3. Imaging selection:

   • For diffuse abdominal pain: CT abdomen/pelvis with IV contrast
   • If specific RUQ tenderness: Consider ultrasound first
   • If CT unavailable: Abdominal ultrasound as alternative

4. Special considerations:

   • For patients with IBD history: Add fecal calprotectin when available
   • For immunocompromised patients: Consider additional testing for opportunistic infections
   • For elderly patients: Lower threshold for CT imaging as clinical presentation may be atypical

Common Pitfalls to Avoid

• Relying solely on laboratory tests without imaging in patients with diffuse abdominal pain
• Delaying CT scan while waiting for laboratory results in patients with concerning clinical presentations
• Failing to consider infectious causes, especially C. difficile, in patients with diarrhea
• Overlooking extra-abdominal causes of abdominal pain (e.g., pneumonia)
• Assuming normal inflammatory markers rule out serious pathology, particularly in elderly or immunocompromised patients 1

CT imaging has been shown to change the diagnosis in 49-54% of patients with nonlocalized abdominal pain and alter management decisions in 42% of cases 1, making it a crucial diagnostic tool in the ED evaluation of these patients.