Background Blood loss from the gastrointestinal (GI) tract is the most common cause of iron deficiency anaemia (IDA) in adult men and postmenopausal women. Gastroduodenal endoscopy (GDE) and colonoscopy are frequently recommended, despite uncertainty regarding the coexistence of lesions in the upper and lower GI tract. The faecal immunochemical test (FIT) measures the concentration of faecal haemoglobin (f-Hb) originating only from the colon or rectum. We aimed to assess whether the FIT was able to select the best endoscopic procedure for detecting the cause of IDA. Methods A prospective study of 120 men and postmenopausal women referred for a diagnostic study of IDA were evaluated with an FIT, GDE and colonoscopy. The endoscopic finding of a significant upper lesion (SUL) or a significant bowel lesion (SBL) was considered to be the cause of the IDA. Results The diagnoses were 35.0% SUL and 20.0% SBL, including 13.3% GI cancer. In the multivariate analysis, the concentration of blood haemoglobin (b-Hb) <9 g/dL (OR: 2.60; 95% CI 1.13-6.00; p = 0.025) and non-steroidal anti-inflammatory drugs NSAIDs (2.56; 1.13-5.88; p = 0.024) were associated with an SUL. Age (0.93; 0.88-0.99; p = 0.042) and f-Hb ≥ 15 μg Hb/g faeces (38.53; 8.60-172.50; p < 0.001) were associated with an SBL. A "FIT plus gastroscopy" strategy, in which colonoscopy is performed only when f-Hb ≥15 μg Hb/g faeces, would be able to detect 92.4% of lesions and be 100% accurate in the detection of cancer while avoiding 71.6% of colonoscopies. Conclusions The FIT is an accurate method for selecting the best endoscopy study for the evaluation of IDA. An FIT-based strategy is more cost-effective than the current bidirectional endoscopy-based strategy and could improve endoscopic resource allocation.
Keywords: accuracy; endoscopy; faecal immunochemical test; iron deficiency anaemia.