Multilevel Predictors of Colorectal Cancer Screening Use in California

Colorectal cancer (CRC), the second-leading cause of cancer death in the United States, resulted in an estimated 51,370 deaths in the United States in 2010.¹ Screening reduces CRC burden by identifying early-stage disease and/or removing precancerous polyps.^2-4 Although CRC mortality rates could be reduced by as much as 50% with complete adherence to screening guidelines, only one-half of United States adults 50 years and older report being up-todate with CRC screening.^2,5 Evidence-based guidelines for screening individuals at average risk for CRC recommend annual fecal occult blood testing (FOBT), flexible sigmoidoscopy (FSIG) every 5 years, or colonoscopy every 10 years.⁴

Use of CRC screening has been shown to vary by individual race/ethnicity, sex, education, income, marital status, insurance coverage, and immigration status.^2,6-16 Other individual characteristics associated with CRC screening uptake include perceived risk, intention for future screening, information-seeking patterns, perceived medical discrimination, life stressors, social support, and healthcare context.^2,6,14,16-21 Of these, having higher education, having higher income, being married, having health insurance and a usual source of care, seeing a physician, receiving a recommendation from a physician to obtain screening, not reporting medical discrimination experiences, and perceiving oneself to be at risk for CRC are most consistently associated with increased CRC screening use.

A few prior studies have assessed how contextual factors influence access to CRC screening.^18,22-25 Prior multilevel analyses^26-28 used poverty rates or rural/urban status as proxy measures of fundamental factors and environmental resources available to communities and the individuals within those communities,^29,30 but findings are not consistent. One recent study examined deprivation and general practitioner density per 100,000 residents, and showed that only the deprivation index was associated with CRC screening use.³¹

To more closely examine which contextual factors might influence CRC screening use, we drew on the World Health Organization social determinants of health framework. This framework underscores the importance of the contexts in which individuals live, work, socialize, and access healthcare for health behaviors and outcomes.³² The World Health Organization framework matched our broad conceptualization of social determinants of health because, unlike most other social determinants of health frameworks, it includes healthcare access. Social determinants of health can shape the opportunities and resources that affect health-related behaviors of individuals, including participation in cancer screening.^9,32,33 Healthcare resources can be conceptualized both at the area level as the local supply of healthcare services and also at the individual level as a measure of insurance or a usual source of care. We used a multilevel framework to study the influences of socioeconomic status (SES), racism, and healthcare resources on CRC screening uptake at individual and area levels with population-based data from the California Health Interview Survey (CHIS). We selected data from California, the largest and most racially/ethnically diverse state in the United States with a large HMO market share that varies by geography. In 1994, California’s dominant HMO, Kaiser Permanente, initiated organized CRC screening using FSIG and FOBT and in 2004, using fecal immunochemical tests.^34,35 Other HMOs also implemented interventions to increase use of CRC screening during this time.^36,37

METHODS

We studied CRC screening use among California residents nested within Medical Service Study Areas (MSSAs) and counties, 2 geographic levels important for healthcare resource delivery in California. Medical Service Study Areas are subcity and subcounty administrative areas identifying “rational service areas” for a variety of healthcare resources and medically underserved designations.³⁸ California designates health professional shortage areas at both MSSA and county levels. The California Department of Health and Human Services organizes its health services delivery (eg, Medi-Cal, Child Health and Disability Prevention Program, cancer screenings) at the county level.

Study Sample and Individual-Level Data

Individual-level data were obtained from the 2005 CHIS adult component, a random-digit dial telephone survey of 43,020 adults conducted in English, Spanish, Mandarin, Cantonese, Vietnamese, and Korean.³⁹ The overall response rate was 29.5% for households and 26.9% for adults. The CHIS response rates are comparable to other telephone-administered population surveys, including the California Behavioral Risk Factor Surveillance System.³⁹ More detailed information on CHIS is available at www.chis.ucla.edu. Our study sample included 20,626 adults. We excluded respondents younger than 50 years (n = 21,014), older than 84 years (n = 1016), with a prior CRC diagnosis (n = 329), or with a proxy interview (n = 141). Sample size for FSIG analyses varied due to skip patterns and resulting missing responses. The MSSA and county data were linked to CHIS respondents using census tract and county variables.

Colorectal Cancer Screening. To evaluate whether individuals were up-to-date with CRC screening, we examined 2 outcomes: (1) up-to-date screening by any modality (ie, FOBT in the past year, FSIG in the past 5 years, or colonoscopy in the past 10 years); and (2) up-to-date screening by FSIG (FSIG within the past 5 years vs not up-to-date by any modality).

To measure up-to-date screening we used the following questions from CHIS:

• Have you ever had a sigmoidoscopy or colonoscopy? These are exams in which a healthcare professional inserts a tube into the rectum to look for signs of cancer or other problems. [If yes:]
  • How long ago did you have your most recent exam?
  • Was your most recent exam a sigmoidoscopy, a colonoscopy, or something else?
• Have you ever done a blood stool test, using a home test kit? [If yes:]
  • How long ago did you do your most recent home blood stool test?