Performance of fecal calprotectin and serum procalcitonin for the diagnosis of spontaneous bacterial peritonitis in patients with cirrhosis: A prospective diagnostic accuracy study

Background: Spontaneous bacterial peritonitis (SBP) is a life-threatening complication in patients with cirrhosis and ascites. This study aimed to evaluate the diagnostic performance of biomarkers—calprotectin (serum, ascitic, fecal) and serum procalcitonin (PCT)—for SBP. Methods: This prospective diagnostic accuracy study, enrolled 137 consecutive patients with cirrhosis and ascites at a tertiary care center in India. Participants were categorized into SBP (n = 55) and non-SBP (n = 82) groups based on the reference standard of ascitic fluid neutrophil count. Serum, ascitic fluid, and fecal calprotectin were measured by enzyme-linked immunosorbent assay, and serum PCT was measured by electrochemiluminescence immunoassay. Diagnostic accuracy was assessed using the area under the receiver operating characteristic curve (AUROC). Mortality was assessed at 3 months. Results: Patients in the SBP group had significantly higher median levels of serum PCT (0.95 μg/L vs. 0.46 μg/L; P = 0.001) and fecal calprotectin (50.00 μg/g vs. 20.00 μg/g; P < 0.001) compared to the non-SBP group. Fecal calprotectin demonstrated excellent diagnostic accuracy for SBP with an AUROC of 0.857 (95% confidence interval [CI]: 0.785–0.929), followed by serum PCT with an AUROC of 0.662 (95% CI: 0.565–0.759). An optimal cut-off of >33 μg/g for fecal calprotectin and >0.83 μg/L for serum PCT were identified. A predictive model incorporating serum PCT and fecal calprotectin achieved an AUROC of 0.862 (95% CI: 0.792–0.932). Three-month mortality was higher in the SBP group, though not statistically significant (41.5% vs. 32.1%; P = 0.276). Conclusion: Fecal calprotectin and serum PCT are promising, readily measurable biomarkers for the diagnosis of SBP in patients with cirrhosis.