A new study shows uninsured American adults with chronic illnesses like diabetes or high cholesterol often go undiagnosed and undertreated, leading to an increased risk of costly, disabling and even lethal complications of their disease.

The study, published online in Health Affairs, analyzed data from a recent national survey conducted by the Centers for Disease Control and Prevention (CDC). The researchers, based at Harvard Medical School and the affiliated Cambridge Health Alliance, analyzed data on 15,976 U.S. non-elderly adults from the National Health and Nutrition Examination Survey (NHANES), a CDC program, between 1999 and 2006.

Respondents answered detailed questions about their health and economic circumstances. Then doctors examined them and ordered laboratory tests.

The study found that about half of all uninsured people with diabetes (46 percent) or high cholesterol (52 percent) did not know they had these diseases. In contrast, about one-quarter of those with insurance were unaware of their illnesses (23 percent for diabetes, 29.9 percent for high cholesterol).

Undertreatment of disease followed similar patterns, with the uninsured being more likely to be undertreated than their insured counterparts: 58.3 percent vs. 51.4 percent had their high blood pressure poorly controlled, and 77.5 percent vs. 60.4 percent had their high cholesterol inadequately treated.

Surprisingly, being insured was not associated with a widely used measure of diabetes control (a hemoglobin A1c level below 7), a finding the authors attribute to the stringent definition of good diabetes control used in the NHANES survey. Even with excellent medical care, many diabetics fail to achieve A1c’s below 7%. Using less stringent hemoglobin A1c thresholds of 8 and 9, uninsured adults had significantly worse blood sugar control than their insured counterparts, the researchers found.

Lead author Dr. Andrew Wilper, who worked at Harvard when the study was done and who now teaches at the University of Washington Medical School, said, "Our study should lay to rest the myth that the uninsured can get the care they need. Millions have serious chronic conditions and don't even know it. And they're not getting care that would prevent strokes, heart attacks, amputations and kidney failure."

Referring to a study released in the American Journal of Public Health last month, which has been widely quoted by Sen. Max Baucus and others, he added, "Our previous work demonstrated 45,000 deaths annually are linked to lack of health insurance. Our new findings suggest a mechanism for this increased risk of death among the uninsured. They're not getting life-saving care."

Dr. Steffie Woolhandler, professor of medicine at Harvard and study co-author, said, "The uninsured suffer the most, but even Americans with insurance have shocking rates of undertreatment, in part because high co-payments and deductibles often make care and medications unaffordable. We need to upgrade coverage for the insured, as well as covering the uninsured. Only single-payer national health insurance would make care affordable for the tens of millions of Americans with chronic illnesses."

Dr. David Himmelstein, associate professor of medicine at Harvard and study co-author, said, "The Senate Finance Committee's bill would leave 25 million Americans uninsured and unable to get the ongoing, routine care that could save their lives and prevent disability. No other wealthy nation tolerates this, yet Congress is turning its back on tens of millions of Americans."

"Hypertension, diabetes and elevated cholesterol among insured and uninsured U.S. adults," Andrew P. Wilper, M.D ., M.P.H.; Steffie Woolhandler, M.D ., M.P.H.; Karen Lasser, M.D ., M.P.H.; Danny McCormick, M.D ., M.P.H.; David H. Bor, M.D.; David U. Himmelstein, M.D. Health Affairs, Oct. 20, 2009 (online).