PTU-243 Faecal calprotectin (FC) assays: comparison of four assays with clinical correlation

Abstract

Introduction: FC is a marker of GI inflammation. Four commercial ELISA-based assays are available, two polyclonal (Calpro [“C”]), Eurospital [“E”]) and two monoclonal (Buhlmann [“B”], Immunodiagnostik [“I”]). “C” is a manual assay, rest are automated. Automation eases testing. Monoclonal assays are reportedly more accurate. Head-to-head comparison of all four assays is unexplored to the best of our knowledge. Aim Pilot study to compare the four assays to help us select one (preferably automated) that best meets our clinical needs: reliably exclude GI inflammation (new patients) and quantify inflammation (known IBD). Methods: 42 stool samples collected from January to March 2011 were tested. Patients: 18 new (mainly for diarrhoea), 24 follow-up IBD (in remission/chronic active disease/flare). Assay (n): “C” (42), “B” (36), “I” (36), “E” (35). All four assays: 29/42 (sample insufficient in rest to do all 4). Analysis: Blinded to assay details, a single investigator (MS) mapped FC values to inflammation grade (0=nil, 1=mild/possible, 2=severe/definite) based on conventional markers (CRP/imaging/endoscopy/histology) and final diagnosis. Linearity characteristics of each assay was assessed by Excel trendlines. Restricting analysis to the 29 samples tested by all four assays (giving six pairings), inter-assay concordance was determined for each inflammation grade by Kendall co-efficient. p Value <0.02 (Fisher ratio) was deemed significant. Results: All four assays showed linear characteristics with different gradients, minimum and maximum values (Figure presented) “C” had maximum gradient and highest values while “I” had the lowest levels detectable. Assays “B” and “E” had characteristics in between. Inter-assay concordance (Table presented) was statistically significant in absence of inflammation for all pairings. The highest assay concordance across all grades of inflammation was between monoclonal “I” and polyclonal “C”.