What are the differential diagnoses for abdominal pain in an adult?

Differential Diagnosis for Abdominal Pain in Adults

Organize by Anatomic Location First

The most efficient diagnostic approach begins with pain location, as this narrows the differential immediately and directs appropriate imaging. 1, 2

Right Upper Quadrant Pain

• Acute cholecystitis is the primary consideration 1, 3
• Hepatobiliary pathology including choledocholithiasis and cholangitis 1, 3
• Hepatitis or hepatic abscess 4
• Pneumonia with referred pain 1

Right Lower Quadrant Pain

• Appendicitis is the critical diagnosis that must be excluded first 1, 2, 3
• Ectopic pregnancy in all women of reproductive age—this is mandatory to rule out 1, 2, 3
• Ovarian torsion 1
• Incarcerated inguinal or femoral hernia 1
• Inflammatory bowel disease (Crohn's disease, terminal ileitis) 1
• Nephrolithiasis 4

Left Lower Quadrant Pain

• Diverticulitis is the leading consideration, especially in older adults 1, 2
• Sigmoid volvulus, particularly with chronic constipation history 1
• Colorectal cancer (causes 60% of large bowel obstructions) 2
• Incarcerated hernia 1

Epigastric or Diffuse Pain

• Peptic ulcer disease or gastritis 1
• Acute pancreatitis 1, 2
• Small bowel obstruction (adhesions account for 55-75% of cases) 1
• Mesenteric ischemia—suspect when pain is out of proportion to physical findings 1, 2
• Perforated viscus 4
• Abdominal aortic aneurysm 5

Common Pathologies Across All Locations

Infectious/Inflammatory Causes

• Pelvic inflammatory disease 2
• Intra-abdominal abscess (hepatic, splenic, diverticular, appendiceal) 4, 2
• Spontaneous bacterial peritonitis in cirrhotic patients with ascites (PMN count >250 cells/mm³) 2
• Clostridioides difficile colitis (CT findings present in 88% of cases) 2

Obstructive Causes

• Small bowel obstruction: adhesions (55-75%), hernias (15-25%) 1, 2
• Large bowel obstruction: colorectal cancer (60%), volvulus (15-20%) 1, 2

Vascular Causes

• Mesenteric ischemia (arterial or venous thrombosis)—25% have occult blood in stool 1, 2
• Abdominal aortic aneurysm 5

Malignancy

• Colorectal cancer 1
• Lymphoma or diffuse metastatic disease 2
• Higher likelihood in elderly patients 1, 3

Gynecologic Causes (Women of Reproductive Age)

• Ectopic pregnancy (always test β-hCG before imaging) 1, 2, 3
• Ovarian torsion (MRI has 86% sensitivity, 100% specificity) 2
• Pelvic inflammatory disease (CT increases detection by 280%) 2
• Ruptured ovarian cyst 1

Urologic Causes

• Nephrolithiasis/renal colic 4
• Pyelonephritis or renal abscess (rapid MRI has 99% accuracy) 2

Critical Red Flags Requiring Immediate Surgical Consultation

Do not pursue extended diagnostic workup when these are present—consult surgery immediately: 2

• Hemodynamic instability (hypotension, tachycardia)—suggests bleeding or sepsis 1, 2
• Peritoneal signs (rigid abdomen, rebound tenderness)—indicates perforation or ischemia 1, 2
• Pain out of proportion to exam—strongly suggests mesenteric ischemia 1, 2
• Abdominal distension with vomiting—indicates bowel obstruction 1
• Fever with severe pain—suggests infection, abscess, or perforation 1
• Tachycardia alone is the most sensitive early warning sign of surgical complications 2, 3

Special Population Considerations

Elderly Patients

• Atypical presentations are common—normal labs do not exclude serious pathology 1, 2, 3
• Higher likelihood of malignancy, diverticulitis, and vascular causes 1, 3
• 15% with bacteremia are afebrile despite serious infection 2

Immunocompromised Patients

• Typical signs of abdominal sepsis may be masked 1, 2
• Delayed diagnosis carries high mortality 4
• More extensive workup necessary even with minimal findings 1

Women of Reproductive Age

• Always consider gynecologic pathology first 2, 3
• Mandatory β-hCG testing before any imaging 1, 2, 3

Post-Surgical Patients

• Adhesive small bowel obstruction (history of prior surgery has 85% sensitivity, 78% specificity) 2
• Anastomotic leak (fever + tachycardia + tachypnea predicts this) 2

Common Diagnostic Pitfalls to Avoid

• Never proceed with CT in reproductive-age women without pregnancy testing—this delays ectopic pregnancy diagnosis and causes unnecessary fetal radiation exposure 2, 3
• Do not overlook hernia orifices and surgical scars during examination—incarcerated hernias are easily missed 1
• Do not dismiss atypical presentations in elderly patients or rely on normal initial labs 1, 2
• Do not order conventional radiography routinely—it has limited diagnostic value and rarely changes management 2, 3
• Avoid over-relying on normal laboratory values early in disease progression 1

Functional Disorders (Diagnosis of Exclusion)

Once organic pathology is confidently excluded, consider functional disorders such as irritable bowel syndrome—these account for a significant proportion of chronic abdominal pain but should never be diagnosed without appropriate workup 6