What are the diagnostic criteria for a diverticulitis flare in an adult patient with a history of diverticulitis or diverticulosis?

Determining a Diverticulitis Flare

Begin with a targeted clinical assessment focusing on left lower quadrant pain, fever, and leukocytosis, but recognize this classic triad is present in only 25% of cases—clinical diagnosis alone is unreliable with misdiagnosis rates of 34-68%, so obtain CT abdomen and pelvis with IV contrast when diagnostic uncertainty exists. 1, 2

Clinical Assessment

The initial evaluation should focus on specific diagnostic features:

• Left lower quadrant pain or tenderness is the primary symptom, though it may be accompanied by abdominal distention or rigidity 3, 4
• Fever is part of the classic triad but is not always present 2, 3
• Nausea, vomiting, anorexia, constipation, or diarrhea may accompany the pain 5, 4
• Dysuria can occur due to bladder irritation from adjacent inflammation 4

High-Accuracy Clinical Prediction Rule

When all three of the following criteria are present, the diagnosis has 97% accuracy (though this combination occurs in only 24% of patients): 2

• Left lower quadrant tenderness on examination
• CRP >50 mg/L
• Absence of vomiting

Laboratory Testing

Order the following tests immediately:

• Complete blood count with differential to assess for leukocytosis and left shift >75% suggesting bacterial infection 2, 3, 4
• C-reactive protein (CRP): levels >50 mg/L support the diagnosis, while CRP >170 mg/L predicts severe diverticulitis with 87.5% sensitivity and 91.1% specificity 2, 3, 4
• Basic metabolic panel to assess for metabolic derangements and elevated lactate suggesting sepsis 2, 4
• Urinalysis to exclude urinary tract pathology 3, 4

Imaging Strategy

When to Image

CT abdomen and pelvis with IV contrast is the preferred diagnostic test and should be obtained when: 1, 2

• Diagnostic uncertainty remains after clinical assessment (which will be most patients given the 34-68% misdiagnosis rate with clinical exam alone) 1, 2
• No prior history of diverticulitis exists 1
• Signs or symptoms suggest alternative diagnoses (cancer, gynecologic causes, inflammatory bowel disease, renal pathology) 1
• Predictors of complicated disease are present: symptom duration >5 days before presentation, signs of perforation, bleeding, obstruction, or abscess 1

CT Diagnostic Performance

• Sensitivity and specificity of 98-100% for diagnosing acute diverticulitis 1, 5, 6
• Detects complications including abscess, perforation, fistula, and obstruction 1
• Identifies alternative diagnoses in up to 49% of cases with nonlocalized abdominal pain 1

Key CT Findings

Uncomplicated diverticulitis: 2, 7

• Colonic wall thickening with pericolonic fat stranding
• Inflamed diverticulum visible

Complicated diverticulitis: 2, 7

• Abscess formation (measure size carefully as <4 cm vs ≥4 cm determines drainage strategy)
• Extraluminal gas or intra-abdominal fluid indicating perforation
• Fistula or obstruction

When Imaging May Be Deferred

For patients with documented prior diverticulitis presenting with typical recurrent symptoms: 8

Imaging may be unnecessary if ALL of the following are present:

• Mild symptoms without fever
• No signs of peritonitis (no guarding, rebound tenderness, or absent bowel sounds)
• Ability to tolerate oral intake
• Immunocompetent status
• No severe presentation or hemodynamic instability

However, obtain CT immediately if any of these develop: 8

• Fever or severe/progressively worsening pain
• Inability to tolerate oral intake
• Signs of peritonitis
• Persistent symptoms beyond 2-3 days despite conservative management
• Immunocompromised status
• Multiple prior recurrences

Alternative Imaging Modalities

• Ultrasound with graded compression can be considered when CT is contraindicated, but is operator-dependent and limited in obese patients 1
• MRI can be considered when ultrasound is inconclusive (obese patients, severe pain, extensive bowel gas) with sensitivity 86-94% and specificity 88-92% 1
• For premenopausal women, consider pelvic/transvaginal ultrasound first if gynecologic pathology is suspected 2

Critical Red Flags Requiring Emergency Evaluation

Immediate emergency department evaluation is warranted for: 2

• Signs of peritonitis: diffuse tenderness, guarding, rebound tenderness, absent bowel sounds
• Signs of sepsis or shock: toxic appearance, confusion, rapid breathing, tachycardia
• Complete obstruction: inability to pass gas or stool with abdominal distension
• Bloody stools suggesting diverticular bleeding
• Progressively worsening pain over several days

Important Pitfalls to Avoid

• Do not rely on the classic triad alone—it is present in only 25% of cases 2
• Do not perform colonoscopy during acute flare—this can worsen perforation risk 3, 4, 6
• Consider colon cancer in the differential, especially if CT shows pericolonic lymphadenopathy >1 cm or a luminal mass 2
• Do not assume recurrent symptoms are always diverticulitis—obtain CT if atypical features, treatment failure, or immunocompromise are present 8