What is the appropriate work-up for a patient presenting to the emergency room (ER) with abdominal pain, without any specific demographic or past medical history?

Emergency Department Work-Up for Acute Abdominal Pain

For undifferentiated acute abdominal pain in the ER, obtain a focused history and physical examination to localize pain and identify red flags, followed by CT abdomen/pelvis with IV contrast as the primary imaging modality for nonlocalized or concerning presentations, as this changes diagnosis in 49-54% of cases and alters management in 42% of patients. 1

Initial Assessment: Red Flags Requiring Immediate Action

Identify life-threatening conditions first:

• Hemodynamic instability (tachycardia, hypotension, tachypnea) suggests bleeding or sepsis requiring immediate resuscitation 2, 3
• Pain out of proportion to physical findings is the hallmark of mesenteric ischemia (30-90% mortality) and demands immediate CT angiography 2, 4, 3
• Peritoneal signs (rigid abdomen, rebound tenderness, guarding) indicate perforation or ischemia requiring surgical consultation 2, 4, 3
• Abrupt onset severe pain suggests vascular catastrophe (aortic dissection, ruptured AAA) with >50% mortality 2, 4, 3

Essential Laboratory Testing

Order these tests immediately:

• Complete blood count to evaluate leukocytosis 2, 3
• Metabolic panel, liver function tests, amylase, lipase 2
• Lactate level - elevation suggests ischemia or sepsis 2
• Beta-hCG in ALL women of reproductive age before any imaging to avoid missing ectopic pregnancy 2, 3
• C-reactive protein has superior sensitivity/specificity compared to WBC for surgical disease 3

Critical caveat: Laboratory values may be normal despite serious infection, especially in elderly and immunocompromised patients 1, 4

Imaging Strategy Based on Pain Location

Right Upper Quadrant Pain

• Ultrasonography is the initial imaging of choice for suspected cholecystitis and hepatobiliary disease 1, 3

Right or Left Lower Quadrant Pain

• CT abdomen/pelvis with IV contrast is recommended 1, 3
• CT has >95% sensitivity for appendicitis and diverticulitis 2
• Alters diagnosis in 49% and changes management in 42% of cases 1, 2

Nonlocalized or Unclear Abdominal Pain

• CT abdomen/pelvis with IV contrast is the preferred initial imaging 1, 2, 4
• Increases diagnostic certainty from 70.5% to 92.2% 1
• Scan the entire abdomen and pelvis - limiting coverage based on symptoms misses pathology in 67% of abnormal cases 1

Suspected Mesenteric Ischemia or Vascular Catastrophe

• CT angiography is the gold standard 2, 4
• Plain radiographs are useless - findings appear late after infarction has occurred 4

Common Diagnostic Pitfalls to Avoid

• Never skip beta-hCG testing in women of reproductive age before imaging - delays ectopic pregnancy diagnosis 2, 3
• Don't rely on normal labs early in disease - elderly patients especially may have normal values despite serious infection 1, 4
• Examine all hernia orifices and surgical scars - easily missed incarcerated hernias 3
• Don't repeat CT indiscriminately - diagnostic yield drops from 22% on initial scan to 5.9% on fourth or greater CT 1
• Avoid CT in patients with abdominal pain plus diarrhea unless other concerning features present - changes management in only 11% versus 53% with pain alone 1

Key Differential Diagnoses by Frequency

Most common causes accounting for two-thirds of presentations: 1

• Non-specific abdominal pain (one-third of cases)
• Acute appendicitis (one-third of cases) - most common in ages 10-30 2, 4
• Other documented pathology (one-third): cholecystitis, small bowel obstruction, pancreatitis, renal colic, perforated ulcer, cancer, diverticulitis 1

Life-threatening causes requiring immediate recognition: 2, 4

• Mesenteric ischemia (30-90% mortality)
• Ruptured AAA (>50% mortality)
• Perforated viscus
• Aortic dissection

Special Populations

Elderly patients:

• May present with atypical symptoms 1
• Require more extensive evaluation even with normal labs 2
• Laboratory tests often nonspecific despite serious infection 1, 4

Immunocompromised/neutropenic patients:

• Typical signs of sepsis may be masked 1
• High mortality rate 1
• Low threshold for imaging 1

Patients with obvious peritonitis:

• Do not delay surgery for imaging 2
• Immediate surgical consultation takes priority 2