What is the approach to diagnosing and managing abdominal pain?

Approach to Abdominal Pain

Initial Clinical Assessment

Begin by determining the pain location, as this directly guides your diagnostic imaging strategy and narrows the differential diagnosis. 1, 2

Vital Signs and Red Flags

• Tachycardia is the most sensitive early warning sign of surgical complications and should trigger urgent investigation even before other symptoms develop 2
• Assess for hemodynamic instability (hypotension, tachycardia) which suggests bleeding or sepsis requiring immediate intervention 2, 3
• The combination of fever, tachycardia, and tachypnea predicts serious complications including anastomotic leak, perforation, or sepsis 2
• Pain out of proportion to physical examination findings should be assumed to be acute mesenteric ischemia until disproven 2, 3
• Peritoneal signs (rigid abdomen, rebound tenderness) indicate perforation or ischemia requiring urgent surgical evaluation 2, 3

Critical History Elements

• Abrupt or instantaneous onset of severe pain suggests vascular catastrophe (aortic dissection or mesenteric ischemia) 2
• Colicky pain indicates bowel obstruction as the bowel attempts to overcome occlusion 2
• Ask specifically about the last bowel movement and passage of gas—this has 85% sensitivity and 78% specificity for predicting adhesive small bowel obstruction in patients with prior abdominal surgery 2
• Document cardiovascular disease history, as patients with cardiovascular disease presenting with acute abdominal pain should be suspected of having acute intestinal ischemia 2
• Atrial fibrillation is present in nearly 50% of patients with embolic acute mesenteric ischemia 2

Mandatory Laboratory Testing

Obtain β-hCG testing in ALL women of reproductive age before proceeding with imaging—failure to do so can delay diagnosis of ectopic pregnancy. 4, 2, 3

Initial Laboratory Panel

• Complete blood count to assess for leukocytosis indicating infection or inflammation 4, 2
• Comprehensive metabolic panel including liver function tests (ALT, AST, alkaline phosphatase, bilirubin) 4
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 4
• Serum lipase (more specific than amylase for diagnosing pancreatitis) 4
• High 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 2

Additional Testing Based on Clinical Suspicion

• Lactate and D-dimer if mesenteric ischemia is suspected, though normal levels do not exclude internal herniation or early ischemia 4, 2
• Blood cultures if fever is present and sepsis is suspected 4
• Procalcitonin for assessing inflammatory response in suspected sepsis 2

Imaging Strategy by Pain Location

Right Upper Quadrant Pain

Ultrasonography is the initial imaging study of choice for right upper quadrant pain. 1, 4, 2

• Acute cholecystitis is the primary diagnostic consideration 1, 3
• Also consider hepatobiliary pathology including choledocholithiasis and cholangitis 3

Right Lower Quadrant Pain

Computed tomography (CT) of the abdomen and pelvis with contrast is the initial imaging study of choice for right lower quadrant pain. 1, 4

• Appendicitis is the most critical diagnosis to exclude 3
• Consider ectopic pregnancy in women of reproductive age (hence mandatory β-hCG first) 3
• Consider using ultrasound as the initial imaging method for suspected acute appendicitis before proceeding to CT to minimize radiation exposure, especially in young patients 2

Left Lower Quadrant Pain

CT of the abdomen and pelvis with contrast is recommended for left lower quadrant pain. 4, 2

• Diverticulitis is a leading consideration in older adults 3
• Consider sigmoid volvulus, especially with history of chronic constipation 3

Pelvic Pain

CT of the abdomen and pelvis with contrast is the most appropriate initial imaging method for pelvic pain. 2

Non-Specific or Diffuse Abdominal Pain

CT of the abdomen and pelvis with contrast is the optimal choice, especially if there is fever or suspicion of serious illness. 2

Imaging Strategy by Suspected Condition

• Acute appendicitis: CT abdomen/pelvis with contrast 2
• Acute cholecystitis: Abdominal ultrasound 2
• Kidney stones: Non-contrast CT abdomen/pelvis 2
• Bowel obstruction: CT abdomen/pelvis with contrast 2
• Mesenteric ischemia: CT angiography of the abdomen 2

Differential Diagnosis Framework

By Location

• Right upper quadrant: Cholecystitis, choledocholithiasis, cholangitis, hepatitis 1, 3
• Right lower quadrant: Appendicitis (15.9-28.1% of surgical cases), ectopic pregnancy, ovarian torsion 2, 3
• Left lower quadrant: Diverticulitis, sigmoid volvulus 3
• Epigastric: Peptic ulcer disease, gastritis, pancreatitis 3

By Mechanism

• Obstruction: Adhesions (55-75% of small bowel obstructions), hernias (15-25%), colorectal cancer (60% of large bowel obstructions), volvulus (15-20%) 3
• Vascular: Mesenteric ischemia (arterial or venous thrombosis), aortic dissection 2, 3
• Inflammatory/Infectious: Appendicitis, cholecystitis, diverticulitis, pancreatitis, pelvic inflammatory disease 3

Special Population Considerations

Women of Reproductive Age

• Always consider gynecologic conditions: ectopic pregnancy, ovarian torsion, pelvic inflammatory disease 2, 3
• Mandatory β-hCG testing before imaging 4, 2, 3

Elderly Patients

• Higher likelihood of malignancy, diverticulitis, and vascular causes 2
• Symptoms may be atypical and require more thorough evaluation even if laboratory tests are normal 2
• Do not dismiss atypical presentations—elderly patients often lack classic peritoneal signs despite having established ischemia 2, 3

Post-Bariatric Surgery Patients

• Tachycardia is the most critical warning sign in this population 2
• Classic peritoneal signs are often absent 2
• Consider internal herniation even with normal lactate 2

Critical Pitfalls to Avoid

• Conventional radiography has limited diagnostic value in most patients with abdominal pain and should not be routinely ordered 1, 4, 2
• Failing to obtain pregnancy testing in women of reproductive age before imaging can lead to delayed diagnosis of pregnancy-related conditions 4, 3
• Overlooking hernia orifices and surgical scars during examination can miss incarcerated hernias 3
• Over-relying on normal laboratory values early in disease—normal lactate does not exclude early ischemia 2, 3
• The absence of peritonitis on examination does not exclude bowel ischemia—patients with sigmoid volvulus often lack peritoneal signs despite having established ischemia 2

When Functional Disorder is Suspected

• Consider functional disorders (e.g., irritable bowel syndrome) only after organic pathology has been confidently excluded 5
• Once a diagnosis of functional pain is established, repetitive testing is not recommended 5
• Refer for psychological support (cognitive therapy) associated with available pharmacological therapeutic options 5