Diagnostic accuracy and clinical application of faecal calprotectin in adult patients presenting with gastrointestinal symptoms in primary care.

Objective: Assessment of faecal calprotectin (fCal) test performance in primary care within an irritable bowel syndrome (IBS) diagnostic pathway.

Methods: Study based on consecutively collected fCal data from 962 patients, aged 18-45, presenting to their general practitioner (GP) with persistent gastrointestinal symptoms.

Results: Six hundred and eighty six (71%) patients had a negative (<50 μg/g) and 276 (29%) had a positive fCal. 28% (77/276) of the patients testing positive and 3% (17/686) of those testing negative had an organic diagnosis. At 50 μg/g the sensitivity of the test for organic disease was 82%, (95% confidence interval [CI] 73-89) and the specificity was 77% (95% CI 74-80), with negative predictive value (NPV) and positive predictive value (PPV) of 98% and 28%, respectively. A cut-off increase to 150 μg/g reduces the NPV by 1% whilst increasing the PPV to 71%. This would reduce colonoscopy and flexible sigmoidoscopy bookings by 10% at the cost of four missed cases of inflammatory bowel disease.

Conclusions: This study provides the first evidence on the use of fCal testing in primary care. The low prevalence of organic disease in this setting has a significant impact on test performance. This suggests a need for change in cut-off value, to improve PPV whilst accepting a reduction in test sensitivity, if it is to be used as part of the pathway for management of patients with suspected IBS.