Fecal calprotectin testing for inflammatory bowel disease in patients presenting with lower gastrointestinal symptoms: a retrospective primary care cohort study in the United Kingdom

BACKGROUND: Fecal calprotectin (FC) can help to differentiate inflammatory bowel disease (IBD) from other causes of lower gastrointestinal (GI) symptoms. This study aimed to study FC testing in primary care, associated factors, subsequent secondary care referrals and IBD diagnoses. METHODS: A retrospective cohort study was conducted using primary care data in England. Adults aged 18-60 with lower GI symptoms between 2015 and 2023 were included. FC testing 30 days before to 3 months after a recorded lower GI symptom was examined. A random-effects logistic regression model explored patient-level factors associated with FC testing. Referral pathways and diagnostic outcomes among patients with FC testing were examined. RESULTS: Of 830 936 symptomatic patients, 34 944 (4.2%) had FC testing. FC testing increased from 1.6% of symptomatic patients in 2015 to 7.7% in 2023 (P = .001). Factors negatively associated with FC testing included female sex (adjusted odds ratio [aOR], 0.80; 95% CI, 0.78-0.82), lower socioeconomic status (aOR, 0.90; 95% CI, 0.86-0.95), smoking (aOR, 0.86; 95% CI,, 0.83-0.89) and obesity (aOR, 0.92; 95% CI, 0.89-0.95). Among patients referred to gastroenterology, 23.7% with FC >250µg/g were diagnosed with IBD, but only 4.1% with FC 100-250µg/g. Among patients with rectal bleeding and FC 100-250µg/g, 9% had IBD. Despite normal FC results (<100µg/g), 25.2% of symptomatic patients were still referred to secondary care, of whom 0.5% were diagnosed with IBD and 1% with colorectal cancer. CONCLUSION: FC can effectively triage primary care patients with suspected IBD. Despite negative FC results, a significant proportion of patients were still referred to secondary care, with very few diagnosed with IBD.