Nonparticipation in a population-based trial to increase colorectal cancer screening

Background: Many trials have tested different strategies to increase colorectal cancer (CRC) screening. Few describe whether participants are representative of the population from which they are recruited.

Purpose: To determine risk factors related to nonparticipation among patients enrolled in an integrated health plan and not up to date for CRC testing, in a trial to increase screening rates.

Methods: Between July 2008 and October 2009, a total of 15,000 adults aged 50-74 years from 21 clinics in Washington State who were due for CRC screening were contacted. Nonparticipants were defined as English-speaking patients who did not engage in the call or refused participation while still potentially eligible. Log-binomial regression models were used to estimate the relative risk of nonparticipation. Analyses were completed between October 2010 and June 2011.

Results: Patients who were nonwhite, had less education, used tobacco, had less continuity of care, and had lower rates of preventive care and cancer screening were more likely to be nonparticipants. Patients reporting never having received any type of CRC testing or screening were also more likely not to participate (62% of nonparticipants vs 46% of participants; adjusted RR=1.58, 95% CI=1.47, 1.70). Reasons for refusal included costs, risks of procedures, and not wanting their medical records reviewed.

Conclusions: Patients eligible for but not participating in the trial were more likely to be from minority socioeconomic and racial groups and had behaviors that can negatively affect cancer outcomes. Additional efforts are needed to recruit patients who need CRC screening the most.

Trial registration: This trial is registered at clinicaltrials.gov NCT 00697047.