Laboratory Testing for Suspected Diverticulitis
For patients presenting with symptoms suggestive of diverticulitis, order a complete blood count (CBC), C-reactive protein (CRP), basic metabolic panel (BMP), and urinalysis as your initial laboratory workup. 1, 2, 3
Essential Laboratory Tests
Complete Blood Count (CBC)
- White blood cell count (WBC) is the most commonly elevated marker in acute diverticulitis 1, 4
- Leukocytosis is present in approximately 90% of patients with acute diverticulitis 5
- WBC >15 × 10⁹ cells/L indicates increased risk for complicated disease and is a criterion for antibiotic therapy 1, 6
- Leukocytosis helps distinguish patients who may require hospitalization versus outpatient management 1, 7
C-Reactive Protein (CRP)
- CRP is the single most valuable laboratory marker for predicting disease severity in diverticulitis 1, 8
- CRP >140-150 mg/L significantly increases the likelihood of complicated diverticulitis and is an indication for antibiotic therapy 1, 6
- CRP >170-175 mg/L has 87.5% sensitivity and 91.1% specificity for distinguishing severe from mild diverticulitis 1, 8
- CRP >224 mg/L is strongly associated with complicated diverticulitis requiring drainage or surgery 1
Basic Metabolic Panel (BMP)
- Assess for electrolyte abnormalities, particularly in patients with vomiting or poor oral intake 2, 3
- Evaluate renal function, especially important when considering antibiotic selection and dosing 7
- Identify patients with chronic kidney disease who may be at higher risk for complications 6
Urinalysis
- Helps exclude urinary tract infection or nephrolithiasis as alternative diagnoses 2, 3
- May show sterile pyuria if inflamed colon is adjacent to the bladder 2
- Essential when considering colovesical fistula as a complication 1
Critical Timing Considerations
Be aware that CRP has a 6-8 hour delay from disease onset and peaks at 48 hours, meaning patients with early presentation may have normal CRP despite significant disease 8. In these cases:
- Do not rely solely on initial CRP values to exclude complicated diverticulitis 8
- Patients with symptoms lasting >5 days, severe pain (≥8/10), persistent vomiting, or inability to tolerate oral fluids should proceed directly to CT imaging regardless of laboratory values 1, 8
- Immunocompromised patients should be considered for CT imaging even with completely normal inflammatory markers 8
Risk Stratification Based on Laboratory Results
High-Risk Features Requiring Antibiotics and Possible Hospitalization:
- WBC >15 × 10⁹ cells/L 1, 6
- CRP >140 mg/L 1, 6
- Increasing leukocytosis on serial measurements 1, 7
- Persistent fever with elevated inflammatory markers 1, 6
Low-Risk Features Suggesting Uncomplicated Disease:
- CRP <140-150 mg/L suggests probable uncomplicated disease (though does not rule out complications) 8
- Normal or mildly elevated WBC in immunocompetent patients without systemic symptoms 1, 6
Common Pitfalls to Avoid
- Do not assume normal inflammatory markers exclude diverticulitis or its complications, especially in early presentation (<8 hours from symptom onset) or in immunocompromised patients 8
- Do not delay CT imaging in patients with high clinical suspicion based solely on waiting for CRP to rise 8
- Do not use laboratory values alone to make the diagnosis—clinical suspicion of diverticulitis based on symptoms alone is correct in only 40-65% of cases, and CT confirmation is needed in most patients 1, 4
- Do not forget to consider alternative diagnoses such as appendicitis (especially with right-sided symptoms), urinary tract infection, nephrolithiasis, or inflammatory bowel disease 2, 5