Els van de Vijver

70 Table 3: Accuracy measures for four diagnostic strategies to predict inflammatory bowel disease. Diagnostic strategy Sens Spec Number per 100 patients (IBD prevalence 11%) TP TN FP FN 1. Symptoms only 72.7% 67.3% 8 60 29 3 2. Symptoms + blood markers 100% 68.4% 11 61 28 0 3. Symptoms + calprotectin 100% 90.1% 11 80 9 0 4. Symptoms + blood markers + calprotectin 100% 96.5% 11 86 3 0 Abbreviations: Sens, sensitivity; Spec, specificity; TP, true positives; TN, true negatives; FP, false positives; FN, false negatives Regardless of whether strategy 2, 3 or 4 was used, all IBD-affected patients were correctly exposed to endoscopy. Strategy 2, 3 and 4 correctly advised against referring 61%, 80% and 86% of patients for endoscopy, respectively. The pre-test probability of IBD in the study cohort was 11%; a positive result of strategy 4 produced a post-test probability of IBD of 78% [95% CI: 60-87%]. The probability of IBD, if strategy 4 was negative, was reduced to 0% [95% CI 0-4%]. Decision curve analysis In the decision curve analysis, strategy 4 (symptoms + blood markers + calprotectin) had the greatest net benefit for predicting IBD across the range of risk thresholds up to 70% ( figure 3 ). Chapter 4 70