How should I interpret the results of a faecal immunochemical test (FIT) in the context of colorectal cancer screening?

The faecal immunochemical test (FIT) is used in colorectal cancer screening to detect hidden blood in faeces, which may indicate colorectal cancer or advanced adenomas. A positive FIT result, defined as a faecal haemoglobin concentration of at least 10 micrograms of haemoglobin per gram of faeces, should prompt a suspected cancer pathway referral for further investigation, typically colonoscopy, to confirm or exclude colorectal cancer.

A negative FIT result does not completely exclude colorectal cancer, as no screening test is 100% effective; interval cancers can occur between screening rounds. Therefore, clinicians should not be over-reassured by a previous negative FIT result if symptoms persist or worsen.

FIT thresholds and interpretation differ between screening and symptomatic contexts, with screening programmes commonly using a cut-off around 20 micrograms haemoglobin/g faeces, but referral thresholds in symptomatic patients are lower (10 micrograms/g) to increase sensitivity.

Primary care teams should promote uptake of FIT screening, as increased participation improves early detection rates, especially in men and across all deprivation groups.