What labs should be ordered for a patient with severe abdominal pain lasting several weeks without diarrhea or vomiting?

Laboratory Tests for Severe Abdominal Pain Lasting Several Weeks

For a patient with severe abdominal pain lasting several weeks without diarrhea or vomiting, a CT angiography (CTA) should be performed without delay, along with laboratory tests including complete blood count, lactate, D-dimer, and comprehensive metabolic panel. 1

Initial Laboratory Evaluation

Essential Laboratory Tests

• Complete Blood Count (CBC): More than 90% of patients with mesenteric ischemia will have an abnormally elevated leukocyte count 1
• Serum Lactate: Elevated levels >2 mmol/L are associated with irreversible intestinal ischemia (hazard ratio: 4.1) 1
• D-dimer: No patient presenting with normal D-dimer had intestinal ischemia; D-dimer >0.9 mg/L has specificity, sensitivity, and accuracy of 82%, 60%, and 79%, respectively 1
• Comprehensive Metabolic Panel: To assess for metabolic acidosis and electrolyte abnormalities 2
• C-reactive protein (CRP): To evaluate for inflammatory conditions 2

Additional Tests Based on Clinical Suspicion

• Amylase/Lipase: Elevated amylase has been reported in roughly half of patients with acute mesenteric ischemia 1
• Liver Function Tests: To rule out hepatobiliary causes 1, 2
• Urinalysis: To exclude urinary tract causes 2
• Pregnancy test: For women of reproductive age 1

Imaging Studies

First-Line Imaging

• CT Angiography (CTA): Should be performed without delay in any patient with suspicion for mesenteric ischemia. Every 6 hours of delay in CTA doubles mortality 1
  • Should include arterial and venous phases to demonstrate thrombus in mesenteric vessels 1
  • Oral contrast is not indicated and may be harmful 1
  • Should be performed despite presence of acute kidney injury, as consequences of delayed diagnosis are more detrimental than contrast exposure 1

Plain Radiography

• Not recommended for evaluating intestinal ischemia 1
• Plain radiography has limited diagnostic value and only becomes positive when bowel infarction has developed 1
• Findings are usually nonspecific, late, and associated with high mortality 1

Clinical Considerations

Risk Factors to Assess

• Atrial fibrillation: Nearly 50% of patients with embolic acute mesenteric ischemia have atrial fibrillation 1
• History of arterial embolus: Approximately one-third of patients have prior history 1
• Cardiovascular disease: Patients with NOMI (non-occlusive mesenteric ischemia) often have history of cardiac failure 1
• Recent surgery: Increases risk for NOMI 1
• Chronic postprandial pain: Associated with mesenteric arterial thrombosis 1
• Progressive weight loss: Common in patients with mesenteric arterial thrombosis 1

Warning Signs

• Severe abdominal pain out of proportion to physical examination findings should be assumed to be acute mesenteric ischemia until disproven 1
• Lactic acidosis combined with abdominal pain, even when the patient does not appear clinically ill, should prompt consideration of early CTA 1

Diagnostic Algorithm

1. Obtain CBC, lactate, D-dimer, comprehensive metabolic panel, and CRP immediately
2. Proceed directly to CTA without delay if mesenteric ischemia is suspected
3. If CTA is not immediately available, begin with ultrasound based on pain location:
   • Right upper quadrant pain: Start with ultrasound 1
   • Lower quadrant or diffuse pain: Proceed to CT 1
4. Add specialized tests based on findings:
   • If liver enzymes abnormal: Complete liver panel
   • If suspicion for pancreatitis: Amylase/lipase
   • If suspicion for urinary tract disease: Urinalysis

Pitfalls to Avoid

• Relying solely on laboratory tests: No laboratory parameters are sufficiently accurate to conclusively identify the presence or absence of ischemic bowel 1
• Delaying imaging: Every 6 hours of delay in diagnosis doubles mortality in mesenteric ischemia 1
• Using plain radiographs: These have limited diagnostic value and should only be used to screen for bowel perforation or obstruction 1
• Misdiagnosing as acute pancreatitis: Elevated amylase occurs in about half of mesenteric ischemia cases 1

Remember that severe abdominal pain lasting several weeks without diarrhea or vomiting is concerning for potentially serious conditions including mesenteric ischemia, bowel obstruction, or malignancy, and requires prompt and thorough evaluation.