What is the appropriate work‑up and initial management for left‑sided abdominal pain?

Left-Sided Abdominal Pain: Diagnostic Work-Up and Initial Management

For adults presenting with left-sided abdominal pain, obtain a CT abdomen and pelvis with intravenous contrast as the initial imaging study, because it provides 98–99% sensitivity and 99–100% specificity for identifying the most common causes—including diverticulitis, colitis, bowel obstruction, and perforation—and directly guides management decisions. 1, 2

Initial Clinical Assessment

Key Historical Features to Elicit

• Duration of symptoms: Pain lasting >5 days predicts higher risk of complicated disease 3
• Severity: Pain score ≥8/10 at presentation indicates increased risk of progression 3
• Associated symptoms: Presence of vomiting, fever >100.4°F, inability to tolerate oral intake, or signs of sepsis (tachycardia, hypotension, altered mental status) 3, 4
• Immunocompromised status: Active chemotherapy, high-dose corticosteroids, organ transplant, or other immunosuppression 3
• Significant comorbidities: Cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes 3

Physical Examination Priorities

• Localized left lower quadrant tenderness with or without guarding suggests diverticulitis 3
• Generalized peritonitis or abdominal rigidity mandates emergent surgical consultation 3
• Vital sign abnormalities (fever, tachycardia, hypotension) indicate systemic inflammatory response or sepsis 3, 4

Diagnostic Imaging Algorithm

First-Line: CT Abdomen/Pelvis with IV Contrast

CT with intravenous contrast is the gold-standard initial test because it:

• Detects diverticulitis with near-100% accuracy 1, 2
• Identifies complications (abscess, perforation, fistula, obstruction) that alter management 1, 2
• Visualizes extraluminal air, pericolic fluid collections, and bowel wall pathology 1
• Differentiates between diverticulitis, colitis, inflammatory bowel disease, epiploic appendagitis, and malignancy 2
• Changes clinical management in 25% of cases compared to clinical assessment alone 4

Clinical diagnosis alone has poor accuracy (68% sensitivity, 98% specificity), making imaging essential for appropriate triage. 4

Alternative Imaging When CT Contraindicated

• Unenhanced CT may be used when IV contrast is contraindicated, with similar accuracy to contrast-enhanced CT in elderly patients 1, 2
• Transabdominal ultrasound can reduce unnecessary CT examinations when directed at the area of maximal pain, particularly useful for identifying diverticulitis in selected patients 1, 2
• Transvaginal ultrasound is appropriate first-line in premenopausal women when gynecologic pathology (ovarian torsion, ectopic pregnancy, tubo-ovarian abscess) is suspected 1, 2

Imaging to Avoid

• Plain abdominal radiography has no role in the initial work-up because CT is far more sensitive and specific for all relevant pathology 1, 5, 6
• MRI is not useful for initial evaluation due to lower sensitivity for extraluminal air and urinary calculi, longer acquisition time, and greater susceptibility to motion artifact 1

Laboratory Investigations

Essential Initial Labs

• Complete blood count: Assess for leukocytosis (WBC >15 × 10⁹/L predicts complicated disease) 3, 2
• C-reactive protein: CRP >140 mg/L indicates significant inflammation and higher risk of progression 3, 2

Note: CRP and WBC alone cannot discriminate urgent from non-urgent causes but help risk-stratify patients with confirmed diagnoses. 6

Initial Management Based on CT Findings

Uncomplicated Diverticulitis (No Abscess, Perforation, Fistula, or Obstruction)

Outpatient Management Criteria (All Must Be Met)

• CT-confirmed uncomplicated disease 3
• Ability to tolerate oral fluids and medications 3
• Temperature <100.4°F 3
• Pain controlled with acetaminophen alone (pain score <4/10) 3
• Absence of significant comorbidities or frailty 3
• Immunocompetent status 3
• Adequate home/social support with reliable follow-up within 7 days 3

Treatment Without Antibiotics (First-Line for Immunocompetent Patients)

Most immunocompetent patients with uncomplicated diverticulitis do NOT require antibiotics; observation with supportive care is the preferred approach. 3

Supportive care includes:

• Clear liquid diet for 2–3 days, then advance as tolerated 3
• Adequate oral hydration 3
• Acetaminophen 1 g three times daily for pain (avoid NSAIDs) 3

High-quality evidence (DIABOLO trial, n=528) demonstrates that antibiotics do not accelerate recovery, prevent complications, or reduce recurrence in uncomplicated cases. 3

Selective Antibiotic Use—Reserve for High-Risk Features

Add antibiotics when ANY of the following are present:

• Persistent fever >100.4°F or chills despite supportive care 3
• Refractory symptoms, vomiting, or inability to maintain oral hydration 3
• Symptom duration >5 days before presentation 3
• CRP >140 mg/L or WBC >15 × 10⁹/L (or rising leukocytosis) 3
• CT findings of fluid collection/abscess, extensive colonic inflammation, or pericolic extraluminal air 3
• Immunocompromised status (chemotherapy, high-dose steroids, organ transplant) 3
• Age >80 years, pregnancy, ASA physical status III–IV, or significant comorbidities/frailty 3

Outpatient oral antibiotic regimens (4–7 days for immunocompetent patients):

• First-line: Amoxicillin-clavulanate 875/125 mg twice daily 3
• Alternative: Ciprofloxacin 500 mg twice daily + Metronidazole 500 mg three times daily 3

Immunocompromised patients require 10–14 days of antibiotics, lower threshold for repeat imaging, and early surgical consultation. 3

Complicated Diverticulitis

Small Abscess (<4–5 cm)

• Hospital admission required 3
• IV antibiotics alone for 7 days: Ceftriaxone + Metronidazole OR Piperacillin-tazobactam 3

Large Abscess (≥4–5 cm)

• CT-guided percutaneous drainage PLUS IV antibiotics 3, 4
• Continue antibiotics for 4 days after successful source control in immunocompetent patients 3

Generalized Peritonitis, Free Perforation, or Sepsis

• Emergent surgical consultation for source control (Hartmann procedure or primary resection with anastomosis) 3, 4
• Immediate broad-spectrum IV antibiotics 3, 4

Bowel Obstruction from Sigmoid Diverticulitis

• Hospital admission, IV fluids, bowel rest, nasogastric decompression if needed 4
• Surgical consultation for potential stenting as bridge to surgery or emergency resection 1

Mandatory Follow-Up

• Re-evaluate within 7 days (or sooner if symptoms worsen) 3
• Repeat CT if symptoms persist beyond 5–7 days despite appropriate management 3
• Colonoscopy 6–8 weeks after symptom resolution for first episode of uncomplicated diverticulitis (if no recent high-quality colonoscopy), for complicated disease (7.9% associated cancer risk), or for patients ≥50 years needing routine screening 3, 2

Critical Pitfalls to Avoid

• Do not rely on clinical assessment alone—imaging is mandatory because clinical diagnosis misclassifies 34–68% of cases 4
• Do not prescribe routine antibiotics for uncomplicated diverticulitis without high-risk features; this adds antimicrobial resistance without clinical benefit 3
• Do not assume all patients need hospitalization—most immunocompetent patients with uncomplicated disease can be safely managed outpatient with 35–83% cost savings 3
• Do not overlook immunocompromised patients—they require immediate antibiotics (10–14 days), lower threshold for repeat imaging, and early surgical consultation 3
• Do not perform colonoscopy during acute inflammation—delay until 6–8 weeks after recovery due to high perforation risk 3
• Do not use plain radiography—it has no added value over clinical assessment and is far inferior to CT 1, 5, 6

Special Populations

Elderly Patients (>65 Years)

• Lower threshold for antibiotic treatment and hospital admission even when other criteria suggest outpatient management 3

Premenopausal Women

• Consider transvaginal ultrasound first if gynecologic pathology (ovarian torsion, ectopic pregnancy, tubo-ovarian abscess) is suspected, because these conditions present with similar left-sided pain 1

Immunocompromised Patients

• Immediate antibiotic therapy for 10–14 days 3
• Lower threshold for CT imaging, repeat imaging, and surgical consultation 3
• Corticosteroid use specifically increases risk of perforation and death 3