Laboratory Tests for Abdominal Pain
All patients presenting with abdominal pain require a complete blood count, comprehensive metabolic panel, urinalysis, serum lipase, and mandatory pregnancy testing in women of reproductive age. 1
Core Laboratory Panel
The initial laboratory workup should include:
- Complete blood count (CBC) to assess for leukocytosis indicating infection or inflammation 1, 2
- Comprehensive metabolic panel (CMP) including liver function tests (ALT, AST, alkaline phosphatase, bilirubin) to evaluate hepatobiliary pathology and organ function 1
- Urinalysis to detect urinary tract infection or nephrolithiasis 1
- Serum lipase (more specific than amylase) for pancreatitis evaluation 1
- Beta-human chorionic gonadotropin (β-hCG) testing is mandatory in all women of reproductive age before any imaging to rule out ectopic pregnancy and other pregnancy-related conditions 1, 2, 3
Additional Tests Based on Clinical Suspicion
When specific conditions are suspected, add:
- Lactate and D-dimer if mesenteric ischemia is suspected, though these lack specificity and normal levels do not exclude early ischemia 1, 2
- Blood cultures in patients with fever and abdominal pain, especially if sepsis is suspected 1
- C-reactive protein (CRP) has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease, though normal CRP does not exclude complications 2, 3
- Procalcitonin for assessing inflammatory response in suspected sepsis 2
Critical Pitfalls to Avoid
- Never proceed with imaging in women of reproductive age without pregnancy testing first - failing to obtain β-hCG can lead to delayed diagnosis of ectopic pregnancy 1, 2, 3
- Do not over-rely on normal laboratory values early in disease - many tests are nonspecific and may be normal despite serious infection, especially in elderly patients 2, 3
- Conventional radiography (plain X-rays) should not be routinely ordered - they have limited diagnostic value in most patients with abdominal pain 1, 2
Special Population Considerations
Elderly patients may present with atypical symptoms and normal laboratory tests despite serious pathology including malignancy, diverticulitis, or vascular causes - maintain high clinical suspicion even with reassuring labs 2, 3
Immunocompromised patients require more extensive workup as they may have masked signs of abdominal sepsis with delayed diagnosis and high mortality 2
Post-bariatric surgery patients often present with atypical symptoms - tachycardia is the most critical warning sign, and classic peritoneal signs are frequently absent 2, 3
Red Flag Laboratory Findings
- Elevated lactate suggests ischemia or sepsis, though normal levels do not exclude internal herniation or early ischemia 2, 3
- Leukocytosis with fever and tachycardia predicts serious complications including anastomotic leak, perforation, or sepsis 2, 3
- Elevated pancreatic enzymes - consider using elevated cutoff levels to improve diagnostic accuracy for pancreatitis 1