Diagnostic Accuracy of Point-of-Care Fecal Calprotectin and Immunochemical Occult Blood Tests for Diagnosis of Organic Bowel Disease in Primary Care: The Cost-Effectiveness of a Decision Rule for Abdominal Complaints in Primary Care (CEDAR) Study

BACKGROUND: Fecal biomarker tests that differentiate between organic bowel disease (OBD) and non-OBD in primary care patients with persistent lower-abdomen complaints could reduce the number of unnecessary referrals for endoscopy. We quantified the accuracy of fecal calprotectin and immunochemical occult blood (iFOBT) point-of-care (POC) tests and a calprotectin ELISA in primary care patients with suspected OBD. METHODS: We performed biomarker tests on fecal samples from 386 patients with lower-abdomen complaints suggestive for OBD. Endoscopic and histological diagnosis served as reference. RESULTS: OBD was diagnosed in 99 patients (prevalence 25.9%); 19 had adenocarcinoma, 53 adenoma, and 27 inflammatory bowel disease. Sensitivity for OBD was 0.64 (95% CI 0.54-0.72) for calprotectin POC, 0.56 (0.46-0.66) for iFOBT POC, and 0.74 (0.65-0.82) for calprotectin ELISA; specificities were 0.53 (0.48-0.59), 0.83 (0.78-0.87), and 0.47 (0.41-0.53), respectively. Negative predictive values (NPVs) were 0.81 (0.74-0.86), 0.85 (0.80-0.88), and 0.84 (0.78-0.89); positive predictive values (PPVs) varied from 0.32 (0.26-0.39) and 0.33 (0.27-0.39) (calprotectin tests) to 0.53 (0.44-0.63) (iFOBT POC). Combining the 2 POC tests improved sensitivity [0.79 (0.69-0.86)] and NPV [0.87 (0.81-0.91)] but lowered specificity [0.49 (0.44-0.55)] and PPV [0.35 (0.29-0.42)]. When adenomas ≤1 cm were considered non-OBD, the NPV of all tests improved to >0.90 [combined POC tests, 0.97 (0.93-0.99)]. CONCLUSIONS: Diagnostic accuracy of the tests alone or combined was insufficient when all adenomas were considered OBD. When only adenomas >1 cm were considered OBD, all tests could rule out OBD to a reasonable extent, particularly the combined POC tests. The tests were less useful for inclusion of OBD.