What labs should I obtain initially for a patient presenting with abdominal pain?

Initial Laboratory Evaluation for Abdominal Pain

For most patients presenting with acute abdominal pain, obtain a complete blood count (CBC), comprehensive metabolic panel, lipase, and beta-hCG (in women of childbearing age) before proceeding to imaging. 1

Essential Laboratory Tests

Core Labs to Order Initially

• Complete Blood Count (CBC): Evaluate for leukocytosis suggesting infection or inflammation 1
• Comprehensive Metabolic Panel: Assess for metabolic disorders, electrolyte abnormalities, and renal function 1
• Lipase: Screen for pancreatitis in patients with epigastric or upper abdominal pain 1
• Beta-hCG: Mandatory in all women of childbearing age before any imaging to avoid radiation exposure to a potential embryo or fetus 2, 1

Additional Labs Based on Clinical Presentation

• C-reactive protein (CRP): Superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease, though normal CRP does not exclude complications 1
• Lactate: Elevated levels suggest ischemia or sepsis, particularly critical if mesenteric ischemia is suspected, though normal levels do not exclude early ischemia 1
• Procalcitonin: Helpful for assessing inflammatory response in suspected sepsis 1
• Liver function tests: Consider when right upper quadrant pain or hepatobiliary pathology is suspected 1
• D-dimer: If mesenteric ischemia is suspected based on pain out of proportion to examination findings 1

Critical Timing Considerations

Do not delay imaging while waiting for laboratory results in patients with severe pain, hemodynamic instability, or peritoneal signs. 1 Tachycardia is the most sensitive early warning sign of surgical complications and should trigger urgent investigation even before laboratory results return 1.

Common Clinical Scenarios

Right Lower Quadrant Pain

• CBC and beta-hCG are sufficient before proceeding to imaging for suspected appendicitis 2, 3
• Ultrasonography or CT with contrast is the appropriate next step 4, 2

Right Upper Quadrant Pain

• CBC, comprehensive metabolic panel, and lipase before ultrasonography for suspected cholecystitis 3

Nonspecific or Diffuse Pain

• Full laboratory panel including CBC, metabolic panel, lipase, and lactate if patient appears ill 1
• CT abdomen and pelvis with IV contrast is typically the definitive imaging study 2

Flank Pain

• Urinalysis is essential, though over 20% of patients with confirmed urinary stones may have negative urinalysis 5
• Non-contrast CT is the imaging study of choice for suspected urolithiasis 4, 5

Key Pitfalls to Avoid

• Never proceed to CT imaging in women of reproductive age without first obtaining beta-hCG to avoid unnecessary fetal radiation exposure 2, 1
• Do not assume normal laboratory values exclude serious pathology, particularly in elderly patients who may present with atypical symptoms 1
• Do not rely solely on white blood cell count—CRP has superior diagnostic accuracy for surgical disease 1
• Normal lactate does not exclude internal herniation or early mesenteric ischemia, especially in post-bariatric surgery patients 1