More than 3 million Americans have mild kidney disease. The current study, based on a seven-year follow-up, was the first randomized trial to examine the effects of chronic renal disease on outcomes after angioplasty and coronary bypass surgery.

"Our data suggests that mild chronic kidney disease should raise a red flag for doctors to monitor patients more closely for heart disease," says lead author Lynda Anne Szczech, M.D., M.S.C.E. "We found that even a small decrease in kidney function increases the risk for post-procedure complications, recurrent hospitalizations, and repeat angioplasty within seven years of the initial procedure."

"We know the risk of cardiovascular disease begins well before end-stage renal disease, during the period of chronic kidney disease," Szczech says. Mild chronic kidney disease can have few symptoms. Sometimes it is found solely on routine blood work when one or more values fall outside the normal range. The condition is expected to become more common among American adults due to increasing rates of diabetes and an aging population.

The 3,608 patients in the study were part of a larger trial called the Bypass Angioplasty Revascularization Investigation, which randomly assigned patients to angioplasty or bypass surgery. The subjects included 76 with chronic kidney disease, 30 of whom had diabetes. All-cause mortality for those with both mild chronic kidney disease and diabetes was 70 percent.

"The presence of both conditions is worse than the sum of their parts. I don't know why they are synergistic," Szczech says. "Perhaps it is that while renal dysfunction is a strike against a person in and of itself, when it is caused by a multi-organ disease such as diabetes, it not only contributes to its risk but acts as a marker for the amount of damage done to organs other than the kidney."