Accuracy of calprotectin using the Quantum Blue Reader for the diagnosis of spontaneous bacterial peritonitis in liver cirrhosis

Aim We aimed to evaluate the accuracy of the dosage of calprotectin in ascitic fluid (AF) using the Quantum Blue assay, for the prompt diagnosis of spontaneous bacterial peritonitis (SBP). Methods We prospectively collected 236 AF samples from 119 cirrhotic patients hospitalized in two French centers between May 2016 and May 2017. Bloody and chylous/cloudy AF, and secondary peritonitis were excluded. SBP was diagnosed if neutrophils in AF were >250/mm(3) using standard cytology. The Quantum Blue Reader selectively measured the calprotectin antigen (MRP8/14) in 12 min within the measurable range from 0.18 to 1.80 mu g/mL; values outside this range were registered as 0.17 and 1.81 mu g/mL. Results A total of 36 AF were considered as SBP (15.2%). SBP had higher median levels of calprotectin than non-SBP (1.81 vs. 0.25 mu g/mL, P < 0.001). Calprotectin levels were positively correlated with neutrophils in AF (r = 0.57, P < 0.001) and C-reactive protein (r = 0.43, P < 0.001), but not with the Child-Pugh and Model for End-Stage Liver Disease scores. The optimal threshold of calprotectin to diagnose SBP was set at 1.51 mu g/mL (80th percentile of calprotectin), yielding sensitivity, specificity, and positive and negative predictive values of 86.1%, 92.0%, 65.9%, and 97.3%, respectively. Only one asymptomatic patient with SBP had a low calprotectin level, but a high serum C-reactive protein level that strongly suggested an ongoing infection. We also showed that intraclass correlation coefficients for inter- and intra-observer agreement were excellent, with 0.95 and 0.89, respectively. Conclusions The dosage of calprotectin in AF using the Quantum Blue assay is a rapid and reliable method of ruling out SBP in hospitalized cirrhotic patients.