Diagnostic Approach to Lower Abdominal Pain

Immediate Diagnostic Considerations

The American College of Radiology rates CT abdomen/pelvis with IV contrast as 8/9 (usually appropriate) for evaluating lower abdominal pain, providing critical advantages in detecting complications and alternative diagnoses 3, 1
CT abdomen and pelvis with IV contrast is the most accurate diagnostic test with 98% diagnostic accuracy, guiding subsequent management decisions 1
Clinical assessment alone is insufficient, with misdiagnosis rates ranging from 34-68% without imaging 1

Check vital signs for shock indicators (hypotension, tachycardia, altered mental status) suggesting perforation, ruptured aneurysm, or mesenteric ischemia 2
Evaluate pain characteristics, as pain out of proportion to physical exam findings is the hallmark of mesenteric ischemia, which carries 30-90% mortality 2
Assess for peritonitis, as diffuse tenderness, guarding, rebound tenderness, or absent bowel sounds indicate possible perforation requiring emergent surgery 1
Document fever and leukocytosis, as the classic triad of left lower quadrant pain, fever, and leukocytosis suggests diverticulitis, though present in only 25% of cases 1

Do not rely on clinical assessment alone, as misdiagnosis rates range from 34-68% without imaging 1
Be aware of common causes of lower abdominal pain, including diverticulitis, appendicitis, small bowel obstruction, urolithiasis, and colitis/inflammatory bowel disease 1, 5, 4, 6

For uncomplicated diverticulitis, conservative management without antibiotics is appropriate for immunocompetent patients, with outpatient management and follow-up in 2-3 days 1, 2
For complicated diverticulitis with small abscess (<3-4 cm), antibiotic therapy alone for 7 days is recommended, with admission for IV antibiotics if unable to tolerate oral intake 1, 2
For complicated diverticulitis with large abscess (>3-4 cm), percutaneous drainage plus antibiotics for 4 days is recommended, with interventional radiology consultation for CT-guided drainage 1, 2

Immediate surgical consultation is required for signs of peritonitis, free air on CT, complete bowel obstruction, hemodynamic instability, or clinical deterioration despite medical management 1, 2, 6

If IV contrast is contraindicated, CT without contrast is acceptable but less accurate for detecting abscesses, with a rating of 6/9 by the American College of Radiology 6, 1
Ultrasound may be considered if renal colic is strongly suspected, but it is operator-dependent and less comprehensive, and cannot reliably exclude surgical pathology 3, 6, 2
Routine colonoscopy after CT-confirmed uncomplicated diverticulitis is not indicated, except for age-appropriate colon cancer screening, abnormal pericolonic lymph nodes, luminal mass visualized, or uncertain diagnosis 1, 3, 2