When it comes to getting screened for colon cancer, location accounts for significant differences in testing rates among non-whites, but screening rates for whites rarely vary regardless of geography, according to a new study.

The study showed that geography played a significant role in screening rate variations among African Americans, according to a statement released by the University of California - Davis Health System.

For example, in the state of Iowa, African Americans and whites had nearly identical screening rates, suggesting their access to screening is similar, and that providers are recommending screening to Medicare enrollees regardless of their race or ethnicity, the researchers said.

But the situation was different in San Jose, Calif., where whites had similar screening rates to whites in Iowa (45 percent), but where screening rates among African Americans (29 percent) were among the lowest found in the study.

It has long been known that racial minorities have lower colorectal screening rates than whites, presumably because of differences in socioeconomic status, access to care and cultural issues. What hasn't been known, until now, is whether these differences also vary across geographic regions, the researchers said.

The study also showed that whites were more likely to be up-to-date on screening than other races everywhere, except in Hawaii, where Asian-Pacific Islanders had significantly higher screening rates than whites (52 percent versus 38 percent).

"This is a stunning finding," said study researcher Dr. Thomas Semrad, a medical oncologist at UC Davis Cancer Center. "Screening rates among Asians in Hawaii were the highest of any group in any cancer registry area, including whites."

Semrad said the influence of Japanese culture in Hawaii may explain the finding. Because other gastrointestinal cancers are prevalent in the Japanese population, he said, there may be more awareness of the benefits of screening.

Semrad and his team analyzed data from 53,990 Medicare enrollees, ages 69 to 79, in eight states and 11 regions.

The researchers considered people to be up-to-date on colon cancer screening if they had a colonoscopy or sigmoidoscopy within the prior five years, or fecal occult blood testing within the past year. The researchers took into account other social, medical and environmental factors that could have affected regional differences in colorectal cancer screening.

Researchers also found substantial disparities when comparing white and Hispanic screening rates in all regions that had substantial Hispanic populations. But unlike the Asian and African-American groups, there was virtually no difference in screening rates among Hispanics in the different regions.

Explaining the geographic variations in screening rates among non-whites will require much more detailed research, Semrad said. But he said that non-whites in some regions may be segregated within primary care practices and health systems that may be less likely to provide colorectal cancer screening. Less access to primary care and to gastrointestinal specialists also may play a significant role in these variations.

A possible explanation of variation among Asian-Pacific Islanders is ethnicity and cultural differences that may influence attitudes toward preventive care and cancer screening, Semrad said. Other research has shown that Chinese immigrants in Seattle, for example, may opt for more traditional methods such as maintenance of energy (qi) and spririt (jing shen), exercise and diet for prevention rather than medical screening.

"The next step is to look at different geographic areas to see what are the determinants for minorities in terms of getting screened," said Semrad. "Are these culturally based? Are there problems with how health-care systems are set up? What are the barriers? If we can figure this out, we would have a target to improve some of these disparities."

The study was published online today (Jan. 10) in the journal Cancer.