What is the recommended systematic approach to assess and treat abdominal pain, including red‑flag identification, history, physical examination, investigations, and initial management?

Systematic Approach to Abdominal Pain Assessment and Management

Immediate Red Flag Identification

Tachycardia is the single most sensitive early warning sign of surgical complications and demands urgent investigation even before other symptoms develop. 1, 2

Critical red flags requiring immediate surgical consultation include: 1, 2

• Pain out of proportion to physical examination findings (assume acute mesenteric ischemia until proven otherwise) 1, 2
• Peritoneal signs: rigid abdomen, rebound tenderness, or guarding indicating perforation or ischemia 1, 3
• Hemodynamic instability (hypotension, persistent tachycardia) suggesting bleeding or sepsis 4, 1
• The triad of fever, tachycardia, and tachypnea predicting anastomotic leak, perforation, or sepsis 1, 2
• Abrupt or instantaneous onset of severe pain suggesting vascular catastrophe (aortic dissection or mesenteric ischemia) 1

Focused History Taking

Location-based approach: 1, 5

• Right lower quadrant → appendicitis
• Right upper quadrant → cholecystitis
• Left lower quadrant → diverticulitis
• Epigastric → gastritis, peptic ulcer, pancreatitis
• Periumbilical migrating to RLQ → appendicitis
• Diffuse/nonlocalized → requires broader CT evaluation

Critical historical elements: 1

• Colicky pain indicates bowel obstruction as bowel attempts to overcome occlusion
• Vomiting before pain makes appendicitis unlikely 4
• Last bowel movement and passage of gas has 85% sensitivity and 78% specificity for adhesive small bowel obstruction in patients with prior abdominal surgery 1
• Ripping, tearing, stabbing quality suggests aortic dissection 1

High-risk patient factors: 4, 1

• Atrial fibrillation present in nearly 50% of embolic acute mesenteric ischemia
• Cardiovascular disease with acute abdominal pain → suspect acute intestinal ischemia
• Prior laparotomy makes adhesive obstruction the leading diagnosis (55-75% of small bowel obstructions)
• Elderly, institutionalized patients on psychotropic medications → classic for sigmoid volvulus

Physical Examination Priorities

Critical examination findings: 4, 1

• Positive psoas sign, fever, or migratory pain to RLQ increases likelihood of appendicitis 4
• Asymmetric gaseous distention with emptiness of left iliac fossa is pathognomonic for sigmoid volvulus 1
• Empty rectum on digital examination is classic for sigmoid volvulus 1

Important caveat: The absence of peritonitis does NOT exclude bowel ischemia—patients with sigmoid volvulus often lack peritoneal signs despite established ischemia due to chronic distension masking the examination. 1, 2

Mandatory Laboratory Testing

Essential initial tests: 1, 3, 2

• Beta-hCG in ALL women of reproductive age before any imaging 1, 2
• Complete blood count (evaluate for leukocytosis) 1, 3
• C-reactive protein has superior sensitivity and specificity compared to WBC count for ruling in surgical disease 1, 2
• Metabolic panel 1, 3

Additional tests based on clinical suspicion: 1

• Elevated lactate suggests ischemia or sepsis (but normal lactate does NOT exclude internal herniation or early ischemia) 1, 2
• Procalcitonin for suspected sepsis 1
• Lipase for epigastric pain suggesting pancreatitis 3
• Urinalysis 3

Imaging Algorithm by Pain Location

Right upper quadrant: Ultrasound for suspected cholecystitis 1, 2, 5

Right lower quadrant: 1, 2

• Ultrasound is the most appropriate initial imaging (especially in pediatric patients to avoid radiation) 1, 3
• If ultrasound inconclusive with high clinical suspicion → CT abdomen/pelvis with contrast (sensitivity >95% for appendicitis) 3

Left lower quadrant: CT abdomen/pelvis with contrast for suspected diverticulitis 1, 2

Pelvic pain: CT abdomen/pelvis with contrast 1, 2

Nonlocalized/diffuse abdominal pain with fever or serious pathology suspected: CT abdomen/pelvis with IV contrast is the optimal initial imaging choice 1, 2

Suspected kidney stones: Non-contrast CT abdomen/pelvis 1, 2

Suspected mesenteric ischemia: CT angiography of the abdomen 1

Suspected bowel obstruction: CT abdomen/pelvis with contrast 1

Important imaging principles: 4, 1

• Conventional radiography has limited diagnostic value and should NOT be routinely ordered 1
• Step-up approach: perform CT after inconclusive or negative ultrasound 4
• MRI has 94% sensitivity and 96% specificity for acute appendicitis (useful in pregnant patients when ultrasound inconclusive) 4

Special Population Considerations

Elderly patients: 1, 2

• Higher likelihood of malignancy, diverticulitis, and vascular causes
• May present with atypical symptoms and normal laboratory tests despite serious infection
• Do NOT over-rely on normal laboratory values early in disease 1, 2

Post-bariatric surgery patients: 1, 2

• Often present with atypical symptoms
• Classic peritoneal signs frequently absent
• Consider internal herniation even with normal lactate

Women of childbearing age: 1, 5

• Consider ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease

Immunocompromised patients: 1

• May have masked signs of abdominal sepsis
• Diagnosis may be delayed with high mortality rate

Initial Management Framework

Immediate surgical consultation indicated for: 3, 2

• Hemodynamic instability
• Peritoneal signs
• Suspected perforation, volvulus, or bowel ischemia

Hospital admission indicated for: 3

• Severe pain
• Inability to tolerate oral intake
• Suspected surgical conditions
• Unclear diagnosis requiring observation

Diagnostic laparoscopy: 4

• When imaging unhelpful, diagnostic laparoscopy may identify causative pathology
• Accuracy very high with definitive diagnosis rates between 86-100%

Critical Pitfalls to Avoid

• Never dismiss tachycardia as the only abnormal vital sign—it demands urgent investigation 1, 2
• Normal lactate does NOT exclude bowel ischemia or internal herniation 1, 2
• Absence of peritoneal signs does NOT exclude bowel ischemia 1, 2
• Normal laboratory tests in elderly patients do NOT exclude serious infection 1, 2
• Avoid overuse of CT scans in young patients to minimize radiation exposure 1
• Do NOT routinely order plain radiographs—they have limited diagnostic value 1, 2