FIT Testing in Iron Deficiency Anemia: A Retrospective Analysis

In low-risk populations, the faecal immunochemical FIT test is excellent at excluding colonic malignancy, with a negative predictive value (NPV) of 99.8%. However, effectiveness in a high-risk iron deficiency anaemia (IDA) population is unclear. This has significant resource implications for health care services worldwide. This study aims to establish the NPV of FIT for colorectal cancer in patients with IDA.

Single-centre retrospective study. Over 12 months, paired cases of FIT <10 µg Hb/g faeces and IDA were identified. Those not completing colonoscopy or CT pneumocolon were excluded. The prevalence of cancer, low-risk and high-risk polyps, defined by British Society of Gastroenterology (BSG) guidelines, was established, and the NPV was calculated.

One thousand twenty-three cases were identified, of which 451 had undergone complete colonic investigation. Mean age was 68 (SD: 11.8). 286/451 (63%) were female. 381/451 had undergone colonoscopy, 78/451 CT pneumocolon with 404/451 also having gastroscopy (OGD). 8/451 (1.8%) had a colonic malignancy. 11/404 (2.7%) had an upper GI malignancy and 14/451 (3.1%) a cancer outside the GI tract. The NPV for colorectal cancer was 98.2% (95% CI: 96.9-99.5). In 24/451 (5.3%) advanced polyps were found, NPV 94.7% (95% CI: 92.6%-96.8%). In 118/451 (26%) low-risk polyps were found, NPV 73.8% (95% CI: 69.8%-77.9%).

The NPV of FIT in IDA appears lower than reported in low-risk symptomatic populations, and it is unclear if this is adequate to negate the need for colonoscopy. Prospective multicentre studies are needed to evaluate this fully.