What laboratory tests should be ordered for a patient with suspected intestinal obstruction?

Laboratory Tests for Suspected Intestinal Obstruction

For patients with suspected intestinal obstruction, order a complete blood count, serum lactate, comprehensive metabolic panel (including electrolytes, BUN/creatinine), and C-reactive protein as the minimum essential laboratory workup. 1, 2

Core Laboratory Panel

The following tests should be obtained immediately in all patients with suspected intestinal obstruction:

Essential Tests

• Complete blood count (CBC) with differential to assess for leukocytosis (WBC >10,000/mm³), which suggests peritonitis, though sensitivity and specificity are relatively low 1, 2
• Serum lactate is critical for detecting bowel ischemia, which carries up to 25% mortality if present and mandates immediate surgical exploration 2, 3
• Comprehensive metabolic panel including electrolytes (sodium, potassium, chloride, bicarbonate) as abnormalities are common due to vomiting and third-spacing 1, 2
• BUN/creatinine to assess for acute kidney injury from dehydration, which is nearly universal in intestinal obstruction 1, 2
• C-reactive protein (CRP) with values >75 mg/L suggesting peritonitis, though with limited sensitivity and specificity 1, 2

Additional Inflammatory Markers

• Erythrocyte sedimentation rate (ESR) can be obtained, though CRP is more sensitive for acute abdominal pain evaluation 1

Critical Interpretation Points

Signs of Bowel Ischemia or Strangulation

Elevated lactate combined with leukocytosis and metabolic acidosis indicates probable bowel ischemia and mandates immediate surgical exploration. 2

• Metabolic acidosis (low serum bicarbonate and arterial pH) suggests advanced ischemia 3
• Elevated amylase may indicate complications 3
• These laboratory findings should prompt urgent surgical consultation even before imaging is complete 2

Electrolyte Abnormalities

• Hypokalemia is frequently found and requires correction before any surgical intervention 1
• Hyponatremia and hypochloremia are common from vomiting and fluid losses 2
• Correction of electrolyte abnormalities is essential during initial resuscitation 1, 4

Important Caveats and Pitfalls

Limitations of Laboratory Testing

• Laboratory tests alone cannot exclude strangulation or ischemia—physical examination has only 48% sensitivity for detecting strangulation even in experienced hands 1, 2
• Normal laboratory values do not rule out bowel ischemia; clinical suspicion and imaging findings must guide management 2, 5
• CRP and WBC have relatively low sensitivity and specificity for peritonitis, so clinical judgment remains paramount 1, 2

Additional Considerations for Specific Contexts

• For patients with inflammatory bowel disease (IBD) presenting with suspected obstruction, also obtain serum albumin/pre-albumin to assess nutritional status and degree of inflammation 1
• Fecal calprotectin should be obtained when possible in IBD patients to assess disease activity 1
• Blood and stool cultures, plus Clostridium difficile toxin testing are mandatory in IBD patients to exclude infectious causes 1

Preoperative Laboratory Work

• Type and screen (or crossmatch if high suspicion for bowel resection) should be obtained for patients definitively going to surgery 2
• Coagulation studies (PT/INR, PTT) if the patient has liver disease, is anticoagulated, or has bleeding risk factors 2

Clinical Algorithm

1. Immediate laboratory panel: CBC, lactate, comprehensive metabolic panel, CRP 1, 2
2. Assess for ischemia: If lactate elevated with leukocytosis and metabolic acidosis → immediate surgical consultation 2
3. Correct electrolyte abnormalities: Particularly hypokalemia during initial fluid resuscitation 1
4. Additional testing based on context: Albumin, fecal calprotectin, and infectious workup for IBD patients 1
5. Preoperative preparation: Type and screen, coagulation studies if indicated 2

Remember that laboratory abnormalities lag behind clinical deterioration in bowel ischemia, so maintain a high index of suspicion and proceed with imaging (CT with IV contrast) when clinical presentation suggests obstruction, regardless of initial laboratory results. 1, 2, 3