Adenoma and advanced adenoma detection in a county-level medical alliance colorectal cancer screening program in Eastern China: a 5-year repeated cross-sectional analysis

Background County-level medical alliances deliver much of China’s organised colorectal cancer (CRC) screening, yet repeated annual colonoscopy yields are seldom reported. We describe five years of outcomes from one county hospital and examine whether adenoma detection changed over time. Methods We analysed 1003 colonoscopies recorded by the screening programme in 2021–2025 at a county-level hospital serving 126 villages and residential communities. Records could not be linked to individuals, so the study is a repeated cross-sectional analysis of successive annual samples. Adenoma detection rate (ADR) was the proportion of colonoscopies with a non-advanced or advanced adenoma, and advanced adenoma detection rate (AADR) the proportion with an advanced adenoma (≥10 mm, villous or tubulovillous histology, high-grade dysplasia, or ≥ 3 synchronous adenomas, under the programme’s operational definition); CRC was excluded from both, and a CRC-inclusive program yield definition was analysed in parallel. Logistic regression adjusted for age group, sex and year; annual rates were standardised to the pooled age–sex distribution. Results ADR was 43.6% (437/1003) and AADR 22.0% (221/1003); CRC was detected in 1.0% (10/1003). ADR showed no significant heterogeneity across years (χ² P = 0.617). AADR was 24.8% in 2021 and 17.1% in 2025 (adjusted OR for 2025 versus 2021, 0.54; 95% CI 0.34–0.87; P = 0.011), and the age–sex standardised AADR fell from 24.3 to 15.0%. Male sex (adjusted OR 2.14 for ADR, 2.02 for AADR) and age ≥ 70 years (2.13, 3.07) were associated with detection. In 2025, adjusted ADR differed between endoscopists ( P < 0.001) but AADR did not ( P = 0.27). The adjusted 2025 AADR estimate was similar with 2020 records included and under CRC-inclusive definitions; the conventional three-criterion AADR could not be reconstructed from the aggregated outcome field. Conclusions Advanced adenoma detection was lower in the final year, but it is confined to one calendar year and the data cannot distinguish changes in participant or referral mix, endoscopy quality, operator effects, classification changes, or chance; it is best treated as an unexplained temporal signal requiring prospective confirmation. We identify additional data fields (referral route and screening-test result, a stable participant identifier, procedural quality indicators and operator identity) that would aid interpretation of yield in such programmes.