A California Nurses Association study said the state's biggest insurers reject one fifth of the medical claims they receive.

Between 2002 and the end of June 2009, the largest five health insurers in California rejected a total of 31.2 million claims, an association analysis found.

PacifiCare had the highest rejection rate, 39.6 percent, and Aetna, the lowest, 6.5 percent, The Los Angeles Times reported Thursday.

"Every claim that is denied represents a real patient enduring pain and suffering. Every denial has real, sometimes fatal, consequences," said Deborah Burger, co-president of the nurses' group.

A group representing insurers questioned the validity of the study.

"Health plans seriously question the data, especially given that it's coming from an organization that has a long-term political goal of government-run healthcare," said Nicole Kasabian Evans, a spokeswoman for the California Association of Health Plans.

Don DeMoro, the nursing group's research director, said the figures were public.

"If you don't agree with the conclusions, get out your slide rule and do your own calculations," he said.