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

Abstract

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/mm³ 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 μg/mL; values outside this range were registered as 0.17 and 1.81 μg/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 μg/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 μg/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.

Keywords: calprotectin; portal hypertension; spontaneous bacterial peritonitis.