Initial Laboratory Tests for Suspected Acute Diverticulitis
For patients with suspected acute diverticulitis, obtain a complete blood count (CBC) with white blood cell count, C-reactive protein (CRP), basic metabolic panel, and urinalysis as your initial laboratory workup. 1, 2, 3
Core Laboratory Panel
Essential Tests
Complete Blood Count (CBC): Leukocytosis (WBC >15 × 10⁹ cells/L) indicates increased risk of complicated disease and may guide decisions about hospitalization and antibiotic therapy 1, 4, 2
C-Reactive Protein (CRP): This is the single most important laboratory marker for risk stratification in acute diverticulitis 1
- CRP <140-150 mg/L suggests probable uncomplicated disease 5, 6
- CRP 150-175 mg/L represents a threshold of increased risk for complicated diverticulitis 1
- CRP >173 mg/L predicts severe disease with 90.9% sensitivity and 90.9% specificity 1, 4
- CRP >224 mg/L is strongly associated with complicated diverticulitis requiring intervention 1
Basic Metabolic Panel: Assess for electrolyte abnormalities, renal function (especially before contrast CT), and evaluate for dehydration or sepsis 2, 3
Urinalysis: Helps exclude urinary tract infection or urolithiasis as alternative diagnoses, and may show sterile pyuria if the inflamed colon is adjacent to the bladder 2, 3
Critical Timing Considerations
A major pitfall: CRP values may not be elevated within the first 6-8 hours of symptom onset, reaching peak levels at 48 hours. 1, 4, 6 Therefore, a low or normal CRP in very early presentation does NOT exclude acute diverticulitis or its complications. If clinical suspicion is high despite normal inflammatory markers, proceed directly to CT imaging rather than relying on laboratory values alone. 6
Risk Stratification Using Laboratory Values
The laboratory results guide your next steps:
Low-risk profile (outpatient management candidate): WBC normal or mildly elevated, CRP <140 mg/L, normal renal function, patient afebrile and tolerating oral intake 5, 4
Intermediate-risk profile (consider hospitalization): WBC >15 × 10⁹ cells/L, CRP 140-175 mg/L, or any laboratory abnormality suggesting systemic inflammation 1, 5
High-risk profile (hospitalization required): CRP >175 mg/L, significant leukocytosis, elevated creatinine, or any laboratory evidence of organ dysfunction 1, 4
Additional Laboratory Markers
While the 2020 World Society of Emergency Surgery guidelines note that neutrophil-to-lymphocyte ratio, serum creatinine, and serum glucose were associated with severe disease in multivariate analysis, only CRP was an independent predictor of complicated diverticulitis (Hinchey >Ib). 1, 6 Therefore, these additional markers add limited value beyond the core panel.
Common Pitfalls to Avoid
Do not rely solely on clinical examination and laboratory values to diagnose diverticulitis—the positive predictive value of clinical diagnosis alone is only 65%, compared to 95% with CT imaging 1
Do not assume normal inflammatory markers exclude complicated disease, especially in immunocompromised patients, elderly patients, or those presenting within the first 6-8 hours of symptom onset 1, 6
Do not use CRP as a predictor of severity if concomitant conditions exist that may affect baseline CRP levels (e.g., chronic inflammatory conditions, recent surgery, other infections) 1
Do not delay CT imaging in patients with high clinical suspicion based solely on waiting for CRP to rise—if the patient appears ill, has peritoneal signs, or has risk factors (age >80, immunosuppression, symptoms >5 days), proceed directly to imaging 1, 6