Primary care endorsement letter and a patient leaflet to improve participation in colorectal cancer screening: results of a factorial randomised trial

BACKGROUND: The trial aimed to investigate whether a general practitioner's (GP) letter encouraging participation and a more explicit leaflet explaining how to complete faecal occult blood test (FOBT) included with the England Bowel Cancer Screening Programme invitation materials would improve uptake. METHODS: A randomised controlled 2 × 2 factorial trial was conducted in the south of England. Overall, 1288 patients registered with 20 GPs invited for screening in October 2009 participated in the trial. Participants were randomised to either a GP's endorsement letter and/or an enhanced information leaflet with their FOBT kit. The primary outcome was verified with return of the test kit within 20 weeks. RESULTS: Both the GP's endorsement letter and the enhanced procedural leaflet, each increased participation by ∼6% – the GP's letter by 5.8% (95% CI: 4.1–7.8%) and the leaflet by 6.0% (95% CI: 4.3–8.1%). On the basis of the intention-to-treat analysis, the random effects logistic regression model confirmed that there was no important interaction between the two interventions, and estimated an adjusted rate ratio of 1.11 (P=0.038) for the GP's letter and 1.12 (P=0.029) for the leaflet. In the absence of an interaction, an additive effect for receiving both the GP's letter and leaflet (11.8%, 95% CI: 8.5–16%) was confirmed. The per-protocol analysis indicated that the insertion of an electronic GP's signature on the endorsement letter was associated with increased participation (P=0.039). CONCLUSION: Including both an endorsement letter from each patient's GP and a more explicit procedural leaflet could increase participation in the English Bowel Cancer Screening Programme by ∼10%, a relative improvement of 20% on current performance.