Faecal calprotectin test cut-off 'should be raised'
Faecal calprotectin cut-off levels in inflammatory bowel disease should be raised in order to reduce colonoscopy and flexible sigmoidoscopy referrals, suggest UK researchers.
Researchers collected faecal calprotectin (fCal) data from 962 patients, aged 18-45 years, presenting to their GP with persistent gastrointestinal symtpoms over one year. The primary objective of the study was to assess the diagnostic performance of the fCal test in routine general practice and audit its clinical application. A secondary objective was to assess the potential impact of different cut-off values of fCal on endoscopic procedures undertaken and referrals to secondary care.
Some 71% patients had a negative (<50 mg/g) and 29% had a positive fCal. Of those, 28% tested positive and 3% of those who tested negative had an organic diagnosis. At 50 mg/g the sensitivity of the test for organic disease was 82%, and the specificity was 77%, with negative predictive value (NPV) and positive predictive value (PPV) of 98% and 28%, respectively. A cut-off increase to 150 mg/g reduced the NPV by 1% whilst increasing the PPV to 71%. The authors predict that this would reduce colonoscopy and flexible sigmoidoscopy bookings by 10% at the cost of four missed cases of inflammatory bowel disease.
What this means for GPs
The researchers note that their study ‘provides the first evidence on the use of fCal testing in primary care’ and that ‘the low prevalence of organic disease in this setting has a significant impact on test performance’. The researchers advise that their results ‘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’. The use of fCal as a point of care diagnostic test to differentiate inflammatory bowel disease from IBS is currently being reviewed by NICE.