title: Measurement of calprotectin in ascitic fluid to identify elevated polymorphonuclear cell count.
abstract: OBJECTIVE
  To evaluate the diagnostic capability of calprotectin in ascitic fluid for detecting a polymorphonuclear (PMN) cell count > 250/μL ascites.
  
  
  METHODS
  In this prospective observational study, a total of 130 ascites samples were analysed from 71 consecutive patients referred for paracentesis. Total and differential leukocyte cell counts were determined manually with a Neubauer chamber and gentian-violet stain. Calprotectin was measured in 1 mL ascetic fluid by enzyme-linked immunosorbent assay (ELISA) and a point-of-care (POC) lateral flow assay with the Quantum Blue(®) Reader (Bühlmann Laboratories). All measurements were carried out in a central laboratory by senior personnel blinded to patient history. A PMN count > 250/μL was the primary endpoint of the study. The diagnostic value of ascitic calprotectin measurement was assessed by comparing to the final diagnosis of each patient that had been adjudicated by investigators blinded to calprotectin values.
  
  
  RESULTS
  The PMN count was > 250/μL in 19 samples (14.6%) from 15 patients (21.1%) and varied widely among the study population (range 10-19 800/mL and 1-17 820/mL, respectively). Spontaneous bacterial peritonitis (SBP) was the final diagnosis in four patients (5.6%). All patients with PMN ≤ 250/μL had negative bacterial culture. PMN count was elevated in five patients with peritoneal carcinomatosis, three with lymphoma, one with neuroendocrine carcinoma, and two with secondary peritonitis due to abdominal perforation. PMN cell counts correlated with ascitic calprotectin values (Spearman's rho; r = 0.457 for ELISA, r = 0.473 for POC). A considerable range of ascitic calprotectin concentrations was detected by ELISA [median 0.43 μg/mL, interquartile range (IQR) 0.23-1.23 (range 0.10-14.93)] and POC [median 0.38 μg/mL, IQR 0.38-0.56 (range 0.38-13.31)]. Ascitic calprotectin levels were higher in samples with PMN > 250/μL, by both ELISA [median (IQR) 2.48 μg/mL (1.61-3.65) vs 0.10 μg/mL (0.10-0.36), P < 0.001] and POC [2.78 μg/mL (2.05-5.37) vs 0.38 μg/mL (0.38-0.41), P < 0.001]. The area under the receiver operating characteristics curve for identifying an elevated PMN count was 0.977 (95%CI: 0.933 to 0.995) for ELISA and 0.982 (95%CI: 0.942 to 0.997) for POC (P = 0.246 vs ELISA). Using the optimal cut-off value for ELISA (0.63 μg/mL), ascitic calprotectin had 94.8% sensitivity, 89.2% specificity, positive and negative likelihood ratios of 8.76 and 0.06 respectively, positive and negative predictive values of 60.0% and 99.0% respectively, and 90.0% overall accuracy. Using the optimal cut-off value for POC (0.51 μg/mL), the respective values were 100.0%, 84.7%, 6.53, 0.00, 52.8%, 100% and 87.7%. Correlation between ELISA and POC was excellent (r = 0.873, P < 0.001). The mean ± SD of the difference was -0.11 ± 0.48 μg/mL with limits of agreement of + 0.8 μg/mL (95%CI: 0.69 to 0.98) and -1.1 μg/mL (95%CI: -1.19 to -0.91).
  
  
  CONCLUSIONS
  Ascitic calprotectin reliably predicts PMN count > 250/μL, which may prove useful in the diagnosis of SBP, especially with a readily available bedside testing device.
authors.affiliation: Gastroenterology and Hepatology, University Hospital Basel, 4031 Basel, Switzerland. burrie@uhbs.ch
authors.forename: Emanuel
authors.initials: E
authors.lastname: Burri
authors.forename: Felix
authors.initials: F
authors.lastname: Schulte
authors.forename: Jürgen
authors.initials: J
authors.lastname: Muser
authors.forename: Rémy
authors.initials: R
authors.lastname: Meier
authors.forename: Christoph
authors.initials: C
authors.lastname: Beglinger
mesh_terms: D000328:Adult; D000368:Aged; D001202:Ascitic Fluid / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007958:Leukocyte Count; D039841:Leukocyte L1 Antigen Complex / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D009504:Neutrophils / Q000166:cytology*; D010538:Peritonitis / Q000150:complications / Q000175:diagnosis; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D015203:Reproducibility of Results
chemical_list: D039841:Leukocyte L1 Antigen Complex
keywords: Ascites; Calprotectin; Liver cirrhosis; Polymorphonuclear cells; Spontaneous bacterial peritonitis