How should I assess and manage a patient with abdominal pain, including red‑flag identification, diagnostic work‑up, and initial treatment?

Assessment and Management of Abdominal Pain

Immediate Red Flag Identification

Begin by assessing for life-threatening conditions that require immediate surgical consultation: hemodynamic instability (tachycardia, hypotension, tachypnea), pain out of proportion to physical findings, and peritoneal signs. 1, 2

Critical Red Flags Requiring Urgent Action

• Tachycardia alone is the most sensitive early warning sign of surgical complications and should trigger urgent investigation even before other symptoms develop 1, 2, 3
• Pain out of proportion to physical examination findings must be assumed to be acute mesenteric ischemia until proven otherwise and requires immediate surgical consultation 1, 2, 3
• The combination of fever, tachycardia, and tachypnea predicts serious complications including anastomotic leak, perforation, or sepsis 2, 3
• Peritoneal signs (rigid abdomen, rebound tenderness, guarding) indicate perforation or ischemia and require urgent surgical evaluation 1
• Abrupt or instantaneous onset of severe pain suggests vascular catastrophe, particularly aortic dissection or mesenteric ischemia 2

Focused History Taking

Pain Characteristics

• Document the primary location of pain first, as this guides both differential diagnosis and imaging selection 1, 2, 4
• Abrupt onset suggests vascular events; gradual onset suggests inflammatory processes 1
• Colicky pain indicates bowel obstruction as the bowel attempts to overcome occlusion 2
• Ripping, tearing, or stabbing quality suggests aortic dissection 2

Associated Symptoms

• Ask specifically about the last bowel movement and passage of gas (85% sensitivity, 78% specificity for adhesive small bowel obstruction in patients with prior surgery) 2
• Vomiting occurs earlier and more prominently in small bowel obstruction versus large bowel obstruction 2
• The triad of abdominal pain, constipation, and vomiting suggests sigmoid volvulus 2
• Approximately 25% of acute mesenteric ischemia patients have occult blood in stool 2

Critical Past Medical History

• Any prior laparotomy makes adhesive obstruction the leading diagnosis (55-75% of small bowel obstructions) 2
• Atrial fibrillation is present in nearly 50% of patients with embolic acute mesenteric ischemia 2
• Cardiovascular disease with acute abdominal pain should raise suspicion for acute intestinal ischemia 2
• Oral contraceptives and estrogen use predispose to mesenteric venous thrombosis 2

Physical Examination Priorities

• Assess vital signs immediately for fever, tachycardia, hypotension, or tachypnea 2
• Examine all hernia orifices and surgical scars, as overlooking these can miss incarcerated hernias 1
• Asymmetric gaseous distention with emptiness of the left iliac fossa is pathognomonic for sigmoid volvulus 2
• Critical pitfall: The absence of peritonitis on examination does not exclude bowel ischemia—patients with sigmoid volvulus often lack peritoneal signs despite established ischemia due to chronic distension masking the examination 2, 3

Laboratory Evaluation

Mandatory Initial Tests

• Beta-hCG testing is mandatory in all women of reproductive age before any imaging to avoid missing ectopic pregnancy 1, 2, 3
• Complete blood count to evaluate for leukocytosis suggesting infection or inflammation 1, 2, 3
• C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease, though normal CRP does not exclude complications 1, 2, 3

Additional Tests Based on Clinical Suspicion

• Metabolic panel, liver function tests, amylase, and lipase to evaluate for metabolic disorders, liver disease, and pancreatitis 2
• Elevated lactate suggests ischemia or sepsis, but normal lactate does not exclude internal herniation or early ischemia 2, 3
• D-dimer if mesenteric ischemia is suspected 2
• Procalcitonin is helpful for assessing inflammatory response in suspected sepsis 2

Critical Laboratory Pitfall

• Over-relying on normal laboratory values early in disease can lead to missed diagnoses, especially in elderly patients where many laboratory tests may be normal despite serious infection 1, 2, 3

Imaging Strategy by Pain Location

Right Upper Quadrant Pain

• Ultrasound is the initial imaging modality of choice for suspected acute cholecystitis and hepatobiliary pathologies 1, 2, 3

Right Lower Quadrant Pain

• Abdominal ultrasound is the most appropriate initial imaging method 2, 3
• CT of the abdomen and pelvis with contrast is the initial imaging modality of choice for suspected appendicitis 1, 2

Left Lower Quadrant Pain

• CT of the abdomen and pelvis with contrast is recommended, especially for suspected diverticulitis 2, 3

Pelvic Pain

• CT of the abdomen and pelvis with contrast is the most appropriate initial imaging method 2, 3

Nonlocalized or Diffuse Abdominal Pain

• CT of the abdomen and pelvis with IV contrast is the optimal initial imaging choice for acute nonlocalized abdominal pain, particularly when fever is present or serious pathology is suspected 2, 3

Suspected Kidney Stones

• Non-contrast CT of the abdomen and pelvis 2, 3

Suspected Mesenteric Ischemia

• CT angiography of the abdomen 2

Imaging Considerations

• Conventional radiography has limited diagnostic value in most patients with abdominal pain and should not be routinely ordered 2
• Avoid overuse of CT scans to minimize ionizing radiation exposure, especially in young patients 2

Special Population Considerations

Elderly Patients

• Elderly patients have a higher likelihood of malignancy, diverticulitis, and vascular causes 2, 3
• Symptoms may be atypical and require more thorough evaluation even if laboratory tests are normal 2, 3

Women of Reproductive Age

• Consider gynecologic conditions such as ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease 2

Post-Bariatric Surgery Patients

• Tachycardia is the most critical warning sign in this population 2
• Classic peritoneal signs are often absent, and internal herniation should be considered even with normal lactate 2, 3

Immunocompromised Patients

• May have masked signs of abdominal sepsis, and diagnosis may be delayed, resulting in high mortality 2

Differential Diagnosis by Location

Right Lower Quadrant

• Appendicitis is the most critical diagnosis to exclude (15.9-28.1% of surgical cases) 1, 2

Left Lower Quadrant

• Diverticulitis is the leading consideration in older adults 1

General Considerations

• Bowel obstruction accounts for 15% of acute abdominal pain admissions 2
• Small bowel obstruction is most commonly caused by adhesions, hernias, and neoplasms 2
• Large bowel obstruction is most commonly caused by cancer, volvulus, and diverticular disease 2

Clinical Decision-Making for Imaging

Not every patient with possible appendicitis needs abdominal imaging. 5

• Patients with very low clinical suspicion may be discharged with minimal or no testing 5
• Patients with high clinical suspicion may be referred to a surgeon with minimal or no testing 5
• If the clinical presentation warrants, notify a surgical consultant as early as clinically indicated 5

Initial Treatment Approach

Hemodynamically Unstable Patients

• Hemodynamic instability suggests bleeding or sepsis and requires immediate resuscitation 1
• Prioritize life-threatening conditions requiring expeditious management to avoid morbidity and mortality 6, 7

Stable Patients with Red Flags

• Severe pain out of proportion to physical findings requires immediate surgical consultation for presumed mesenteric ischemia 1, 2, 3
• Peritoneal signs require urgent surgical evaluation 1