Effect of Long-Term Adherence on FIT Positivity, PPV, and Detection in Population-Based CRC Scre

07 Apr 20264 min read0 viewsJournal Feed

GIST

Background Long-term adherence and results with faecal immunochemical test (FIT)-based colorectal cancer (CRC) screening are poorly characterised. Objective To characterise adherence and results through seven rounds in an organised biennial FIT-based CRC screening programme.

Design We determined per-round FIT-completion, FIT-positivity, CRC and high-risk-CRC precursor positive predictive values (PPVs) and CRC detection/1000-FIT-participants for all invitees versus an adherent cohort (entry 50 - 51 years; 66 - 100% rounds completed) versus comparable-age first-ever screenings from 2010 to 2023. Joinpoint and multivariable logistic regression analyses identified trends.

Results Adherence was consistent, frequent, occasional, infrequent and never (defined as 100%, 66 - 99%, 33 - 65%, 1 - 32%, 0% of rounds offered) in 29.2%, 8.6%, 11.5%, 4.5% and 46.2% of 2.81 million individuals, respectively. In both the all-invitee population and the adherent cohort, the first round yielded the highest FIT positivity (5.8%, 4.4%), PPVs for CRC (5.1%, 3.3%) and high-risk precursors (20.4%, 13.1%), and CRC detection rates (2.65, 1.30 per 1000 participants), respectively.

Clinical Editorial

Summary

Adherence patterns and baseline signal across repeated FIT rounds: a population-wide view

Context and design

This study assesses long-term adherence and test metrics across seven biennial FIT rounds in an organized colorectal cancer screening program, comparing all invitees with an adherent cohort (entry at ages 50–51; 66–100% of rounds completed) and a comparator of first-ever screenings at the same ages from 2010–2023.
Analytical approaches included joinpoint and multivariable logistic regression to identify trends over time.

Cohort structure and adherence spectrum

Adherence categories were defined by the proportion of rounds offered: 100% (consistent), 66–99% (frequent), 33–65% (occasional), 1–32% (infrequent), and 0% (never).
Within the population studied (2.81 million individuals), distribution spanned 29.2% in the highest adherence bracket, 8.6% in the frequent category, 11.5% in occasional, 4.5% in infrequent, and 46.2% in never-adherent groups.

Key per-round signals and age-specific comparisons

The initial screening round consistently produced the highest FIT positivity rate, the highest positive predictive values (PPVs) for CRC and high-risk precursors, and the greatest CRC detection rate per 1,000 participants in both the overall invitee population and the adherent cohort.
In subsequent rounds beyond the third, outcome measures declined and stabilized at levels markedly lower than those observed in first-time screeners of the same age cohort.
Specific contrasts illustrate substantial attenuation by the seventh round: CRC-PPV ranged at 1.6–2.2% in the seventh round (median age 62–65) versus 6.6% for new screeners aged 62–63, with corresponding reductions in other metrics such as detection rates.

Colonoscopy follow-through and practical implications

Among those with a positive FIT, colonoscopy completion was high at 87.3%, indicating sustained downstream evaluation in the program.

Context, limitations, and interpretation

The findings suggest that initial screening yields the strongest signal for positivity, PPV, and detection, with a gradual stabilization to lower levels after multiple rounds, likely reflecting prior neoplasia removal and a progressively lower-risk population.