Laboratory and Imaging Workup for Suspected Diverticulitis
For non-pregnant adults with suspected diverticulitis, obtain a CT scan with IV contrast as the initial imaging modality, along with basic laboratory tests including CBC, basic metabolic panel, urinalysis, and C-reactive protein. 1
Laboratory Tests
Initial laboratory workup should include:
- Complete blood count (CBC) to assess for leukocytosis, which is commonly present in diverticulitis 2, 3
- Basic metabolic panel to evaluate renal function (important before contrast administration) and electrolyte abnormalities 2
- Urinalysis to help exclude urinary tract infection as an alternative diagnosis 2
- C-reactive protein (CRP) measurement to assess inflammatory burden 2
Important caveat: Clinical signs, symptoms, and laboratory tests alone should NOT be used to diagnose diverticulitis in elderly patients—imaging is essential regardless of leukocyte or CRP values 1. This principle applies broadly to all age groups, as laboratory findings are nonspecific.
Imaging Studies
First-Line Imaging: CT Scan
CT abdomen/pelvis with IV contrast is the gold standard initial imaging modality with sensitivity of 92-99% and specificity of 97-100% for diagnosing acute diverticulitis 1, 3.
Key advantages of CT include: 1
- Confirms diagnosis and distinguishes complicated from uncomplicated disease
- Identifies complications (perforation, abscess, fistula, obstruction, bleeding)
- Rules out alternative diagnoses
- More readily available and feasible than MRI
- Less operator-dependent than ultrasound
IV contrast is usually appropriate to characterize bowel wall abnormalities and detect complications, though CT without IV contrast may be used when contrast is contraindicated (severe renal disease or contrast allergy) 1.
Alternative Imaging When CT Unavailable or Contraindicated
If CT is unavailable or contraindicated in non-pregnant adults, obtain ultrasound (US) or MRI as alternative diagnostic modalities 1.
Ultrasound characteristics:
- Sensitivity >90% and positive predictive value >90% in meta-analyses 4
- Diagnoses diverticulitis using three criteria: short-segment colonic wall thickening, inflamed diverticulum, and noncompressible hyperechoic pericolic tissue 4
- Major limitations: accuracy diminished in obese patients and distal sigmoid diverticulitis; requires high operator expertise (minimum 500 examinations for competency); less likely to identify alternative diagnoses 4
MRI characteristics:
- Sensitivity of 94% (95% CI: 82-99%) and specificity of 88% (95% CI: 47-100%) 1
- Evidence quality is low due to limited studies and small sample sizes 1
Special Population: Pregnant Patients
For pregnant adults with suspected diverticulitis, US or MRI can be considered, though there is insufficient evidence to recommend one over the other (knowledge gap) 1. These modalities avoid radiation exposure, which is critical in pregnancy.
Clinical Pitfalls and Caveats
Do not rely on clinical examination alone: Elderly patients presenting with abdominal guarding or left lower quadrant pain should undergo imaging regardless of normal laboratory values 1. The sensitivity and specificity of clinical diagnosis without imaging is inadequate.
Proceed to CT if ultrasound is inconclusive: If US is negative despite high clinical suspicion or if complicated diverticulitis is suspected, obtain CT scan 4. Operator dependence and lower specificity of US are significant limitations.
Consider patient-specific factors: In young patients with typical presentation, contraindications to CT, or pregnancy, consider US as first-line to minimize radiation exposure 4. However, maintain a low threshold for CT if diagnosis remains uncertain.
Colonic wall thickness on CT has prognostic value: Wall thickness <9 mm predicts lower recurrence risk (19%) 5, which may inform counseling and follow-up planning.