FIT screening yield falls after the first round, then settles at a lower but persistent level
Long-term adherence to organised faecal immunochemical test screening tells a familiar but clinically important story: the first contact with screening identifies the largest burden of occult disease, while later rounds operate in a population that has already shed much of its highest-risk neoplasia. In this biennial colorectal cancer programme, investigators followed 2.81 million invitees across seven rounds and separated them into adherence patterns ranging from consistent participation to never screened. The distribution alone is striking. Nearly half of invitees, 46.2%, never completed a round, while 29.2% participated consistently and smaller fractions fell into frequent, occasional, or infrequent attendance categories.
The first round was the most productive by every measured endpoint. FIT positivity reached 5.8% in the all-invitee population and 4.4% in the adherent cohort. Positive predictive value for colorectal cancer was 5.1% and 3.3%, respectively, while PPV for high-risk precursors reached 20.4% and 13.1%. Detection rates mirrored those numbers, at 2.65 and 1.30 cancers per 1000 participants. In later rounds, the curve flattened. Beyond three rounds, positivity, PPV, and detection stabilized at lower levels, reflecting a screened population that had already undergone lesion removal and a gradual enrichment for lower-risk individuals who remained under surveillance.
The biological logic is straightforward. Once advanced adenomas and early cancers are removed through colonoscopy follow-up, the remaining cohort is less likely to harbor occult bleeding lesions detectable by FIT. A second force is selection: people who continue returning for screening are not the same as those who never respond, and their risk profile shifts over time as the highest-yield lesions are drained from the pool. Screening efficiency therefore falls, but it does not vanish.
The adherent cohort still generated clinically meaningful cancer detection
Among participants who completed 66% to 100% of offered rounds, the first round still delivered the highest yield. After that initial sweep, later rounds became more stable, but not trivial. By the seventh round, CRC PPV in the adherent cohort ranged from 1.6% to 2.2% at a median age of 62 to 65 years, compared with 6.6% in first-time screeners aged 62 to 63 years. The absolute drop is large, yet the remaining yield is still clinically relevant in a population that had already been screened repeatedly.
This is the practical lesson for programme design. Repeated normal FITs do not reduce risk to zero, and the persistence of measurable cancer detection argues against stopping surveillance simply because several biennial tests have been negative. The data support a lower-yield steady state rather than a flat line at zero. In screening medicine, that difference matters at the population level because modest per-round yields can still translate into substantial case detection when millions of people are invited.
A high colonoscopy completion rate after positive FIT strengthens the interpretation. Follow-up colonoscopy was completed in 87.3% of positive cases, which means the screening programme was able to convert biochemical signal into diagnostic action for most participants. Without that downstream step, positivity rates would be difficult to interpret clinically; with it, FIT becomes a functioning triage tool that filters a large population toward definitive evaluation. The high completion rate also reduces the chance that the observed stabilization in PPV and detection simply reflects missed diagnoses after positive tests.
Longitudinal screening strategy should preserve re-entry, not weaken it
The study used joinpoint and multivariable logistic regression to track trends across rounds and compare all invitees, an adherent cohort, and first-ever screeners of comparable age from 2010 to 2023. That design matters because age alone does not explain the pattern. The comparison with same-age first-time screeners shows that later-round participants are not merely older versions of the original cohort; they are a biologically selected group with prior lesion clearance and ongoing surveillance, which lowers pretest probability. Even so, the detection signal remained clinically meaningful.
For programme planners, the message is direct. An organised biennial FIT screening system should expect the strongest yield in the first round and lower rates afterward, but lower does not mean negligible. Repeated invitation remains justified because some cancers and high-risk precursors will still surface in adherent participants. A policy of early cessation after several normal tests would be difficult to defend from these data alone, especially given that the most informative benchmark is not whether later rounds match the first, but whether they continue to find actionable disease. They do.
The pattern also has bedside implications. Patients often interpret a sequence of negative stool tests as a reason to step away from screening entirely. These data argue for the opposite counseling approach: negative FITs are reassuring, but they are not a reason to abandon a structured program while eligibility remains. The screening pathway works best when patients understand that risk falls over time because the system is finding and removing lesions, not because the colon has become biologically inert.
One caution sits inside the apparent stability. Lower positivity and PPV in later rounds are expected, but they also mean clinicians must avoid over-reading a negative test as a clean bill of health. FIT remains a blood-based detector of bleeding lesions, not a direct visual exam, so interval disease can still emerge between rounds or remain below the threshold of detection. The evidence here supports continuing biennial screening rather than truncating it after a string of normal results, particularly in populations where participation can be maintained and colonoscopy follow-up is available.