Figure 5  .

Receiver operating characteristic analysis of the ability of calprotectin, C reactive protein (CRP), and erythrocyte sedimentation rate (ESR) to discriminate between patients with Crohn's disease and the irritable bowel syndrome. The unbroken line ("no discrimination") indicates values that have no discriminatory value. Note that on the vertical axis, the scale is from no (0) to complete (1 or 100%) sensitivity. The horizontal axis is a reciprocal scale (1−specificity). The optimum performance of a test is determined either as the highest sum of the specificity and sensitivity or at an acceptable level of sensitivity for the given disease. A cut off value of 30 mg/l for faecal calprotectin gives 100% sensitivity and 97% specificity for discriminating between patients with Crohn's disease and the irritable bowel syndrome.