C-Reactive Protein in Small Intestinal Bacterial Overgrowth (SIBO)
C-reactive protein (CRP) is not consistently elevated in patients with small intestinal bacterial overgrowth (SIBO) and therefore is not a reliable diagnostic marker for this condition. 1
Relationship Between SIBO and Inflammatory Markers
SIBO is not associated with systemic inflammation as measured by CRP and erythrocyte sedimentation rate (ESR) in patients with Crohn's disease, despite being more prevalent in these patients (32.6%) compared to controls (12.4%) 1
In a study of Crohn's disease patients with and without SIBO, systemic inflammatory biomarkers including CRP were comparable between both groups, indicating that SIBO does not significantly contribute to systemic inflammation 1
While SIBO is associated with local intestinal inflammation (as measured by fecal calprotectin), this does not translate to elevated systemic inflammatory markers like CRP 1
Local vs. Systemic Inflammation in SIBO
Fecal calprotectin, a marker of intestinal inflammation, is significantly higher in SIBO-positive patients (median 485.8 μg/g vs. 132.7 μg/g in SIBO-negative patients), indicating that SIBO primarily causes localized intestinal inflammation 1
In cystic fibrosis patients with SIBO, fecal calprotectin levels were elevated, but this did not correlate with systemic inflammatory markers, further supporting that SIBO primarily causes localized rather than systemic inflammation 2
CRP is an acute-phase protein produced by hepatocytes upon stimulation by inflammatory cytokines, making it a general marker of inflammation rather than specific to SIBO 3
Clinical Implications
CRP testing has limited utility in diagnosing SIBO, as it lacks specificity for this condition 1, 2
In patients with hyperlipidemia and SIBO, there was no significant correlation between CRP levels and the presence of SIBO, despite SIBO being present in 78.9% of these patients compared to 40% in controls 4
The diagnostic performance of CRP for detecting intestinal inflammation has a sensitivity of 67% (95% CI, 54%-77%) and specificity of 73% (95% CI, 65%-80%), making it less reliable than fecal markers for detecting intestinal conditions 5
Other Inflammatory Markers in SIBO
Fecal calprotectin is a more sensitive marker for intestinal inflammation associated with SIBO than systemic markers like CRP 1, 2
In a study of depressive patients with SIBO, inflammatory markers included elevated intraepithelial lymphocytes (IELs) and fecal calprotectin, but CRP was not consistently elevated 6
The diagnostic accuracy of fecal calprotectin for detecting intestinal inflammation is superior to CRP, with sensitivity of 81% (95% CI, 74%-87%) and specificity of 72% (95% CI, 61%-81%) at a cutoff of 150 mg/g 5
Conclusion
SIBO primarily causes localized intestinal inflammation that may not be reflected in systemic inflammatory markers like CRP. While some patients with SIBO may have elevated CRP due to comorbid conditions or complications, CRP elevation is not a consistent or reliable finding in SIBO and should not be used as a diagnostic marker for this condition.