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PTH-069 Is a false positive faecal calprotectin as false as you think ?
  1. L Asser1,
  2. S Nanton2,
  3. T Price2,
  4. H Holt1,
  5. MW Johnson2
  1. 1Biochemistry
  2. 2Gastroenterology, Luton and Dunstable FT University Hospital, Luton, UK

Abstract

Introduction Faecal calprotectin is a useful diagnostic assessment tool, providing accurate differentiation of organic bowel disease from functional issues. As with any test, there is a false positive rate, that is said to occur at a rate of 9% (Van Rheenen, 2010). Previous studies have defined this as a positive calprotectin where subsequent endoscopic assessment (OGD and colonoscopy) have proven normal. Such an assumption fails to take into account any assessment of the small bowel. We set out to assess the effectiveness of investigating these patients further with a small bowel capsule enteroscopy (SBCE).

Method 55 patients with raised faecal calprotectin levels (BÜHLMANN fCAL ELISA) underwent endoscopic investigations which proved normal. They were subsequently labelled as having false positive faecal calprotectin levels. We investigated these patients further with a SBCE. The results of these assessments were reviewed and an analysis was made of the median calprotectin levels and their diagnostic performance.

Results Of the 55 patients labelled with false positive faecal calprotectin results, SBCE found accountable pathology (angiodysplasia, Crohn’s disease, NSAID enteropathy, polyps, TB, malignancy) in 80%. Small bowel enteropathy (likely Crohn’s disease) was found in 36%. The sensitivity of calprotectin in this cohort was 88%, with a positive predictive value of 79%. The specificity was 40% and the area under the curve after ROC curve analysis was 0.73. Linear correlation of calprotectin against disease activity score gave an R2 value of 0.55. Median values of calprotectin in small bowel Crohn’s patients were 206 µg/g (IQR 95.5–346) as compared to 70 µg/g (IQR 30–147) in disease free ‘normal’ patients P value=0.002.

Conclusion The true false positive rate for faecal calprotectin is significantly reduced (<5%) when colonoscopy and OGD are combined with SBCE. SBCE should be automatically considered in patients with persistent raised faecal calprotectin levels, even if they have had normal endoscopic evaluation. When a higher cut off level for calprotectin is used at >200 µg/g, the specificity for small bowel Crohn’s is increased to 50%. If small bowel Crohn’s disease is left undiagnosed and untreated, then secondary complications such as stricturing, obstruction, perforation, fistula formation, malnutrition and cancer, can develop. Earlier detection and initiation of medical treatment, would be expected to improved long term outcome, reducing the need for surgical intervention. Our study has shown that faecal calprotectin can be used effectively in the early detection of small bowel Crohn’s disease.

Reference

  1. . van Rheenen PF1, Van de Vijver E, Fidler V. Faecal calprotectin for screening of patients with suspected inflammatory bowel disease: diagnostic meta-analysis.BMJ 2010 Jul;15;341:c3369

Disclosure of Interest None Declared

  • FAECAL CALPROTECTIN
  • Inflammatory Bowel Disease
  • Small bowel Crohn’s disease

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