Procalcitonin and C-reactive protein in the diagnosis of spontaneous bacterial peritonitis

Spontaneous bacterial peritonitis (SBP) is a serious complication of cirrhosis and is associated with high morbidity and mortality. Rapid institution of appropriate antibiotics is central to the improved patient outcome. Correctly obtaining ascites fluid for analysis has several technical and logistic limitations resulting in overuse of empiric antibiotics when patients are admitted to the hospital with suspected SBP. Procalcitonin and C-reactive protein (CRP) are non-invasive markers of infection. We conducted a study to illustrate the role of these markers in making the diagnosis of SBP in patients with cirrhosis.

A total of 45 patients were enrolled in this prospective cohort study, 14 (31.1%) of which were found to have SBP. Ascitic fluid neutrophils, serum procalcitonin and CRP levels were measured prior to initiation of antibiotics and these parameters were compared between the two groups. Area under receiver operator characteristic (AUROC) curves were used to assess the diagnostic accuracy of procalcitonin and CRP in this population. We defined neutrocytic SBP group as a combination of patients who had classic SBP (positive ascitic culture and >250 neutrophils/mm³) and culture-negative neutrocytic ascites.

Serum procalcitonin (2.81±2.59 vs. 0.43±0.48 ng/mL; P=0.0032), serum CRP (60.30±44.48 vs. 22.2±23.28; P=0.0055) and ascitic fluid neutrophil levels (49.23±30.90 vs. 16.7±20.39; P=0.0064) were significantly higher in SBP group than non-SBP group. AUROC for procalcitonin (cut-off >2.0 ng/mL) was 0.75 (95% CI, 0.61-0.88), CRP (cut-off >3.0 mg/L) was 0.55 (95% CI, 0.43-0.68) and for procalcitonin combined with CRP was 0.76 (95% CI, 0.61-0.90) for diagnosing all-cause SBP. In a subgroup analysis of patients with neutrocytic SBP, AUROC for procalcitonin was 0.88 (95% CI, 0.74-1.00), CRP was 0.62 (95% CI, 0.45-0.79) and for procalcitonin combined with CRP was 0.93 (95% CI, 0.81-1.00). Addition of CRP to procalcitonin did not significantly change the AUROC for diagnosis of SBP.

Serum procalcitonin could be used as an adjunctive non-invasive biomarker in diagnosing SBP with a high degree of accuracy in cirrhotic patients. Addition of CRP does not seem to significantly increase the diagnostic accuracy of procalcitonin.