Studies Identify Interactions Between Heart Disease, Kidney Disease

06/11/07 Clinical Trials, Prevention, Disease Basics, General

Most patients with chronic kidney disease die of complications from heart disease rather than of kidney failure, according to two reports in the June 11 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

The reports found that anemia and other conditions related to chronic kidney disease are independently associated with the risk of cardiovascular disease; conversely, heart disease is associated with a decline in kidney function and the development of kidney disease.

Chronic kidney disease is becoming increasingly prevalent in the United States and worldwide, according to background information in the articles. Chronic kidney disease is associated with a wide variety of complications, including anemia (low red blood cell count, or red blood cells that are deficient in oxygen-transporting hemoglobin), nerve pain, bone disease, death, and cardiovascular disease.

In one study, Peter A. McCullough, M.D., M.P.H., of William Beaumont Hospital, Royal Oak, Mich., and colleagues assessed a group of 37,153 individuals who were screened for kidney disease through a community-based program between 2000 and 2003. The participants (average age of 52.9 years) all reported a personal or family history of diabetes, hypertension, or kidney disease on a screening survey. Patients had their blood pressure measured and provided blood and urine samples, which were processed to assess three markers of chronic kidney disease:

• estimated glomerular filtration rates (eGFR), or the rate at which kidneys filter blood, calculated based on levels of the waste product creatinine in the blood
• anemia, determined by blood hemoglobin levels
• and microalbuminuria, or slightly high levels (20 milligrams per liter or more) of the protein albumin in the urine

Of the participants who were followed for a maximum of 47.5 months, 5,504 (14.8 percent) had abnormal eGFR values, and signs of declining kidney function. In addition, 4,588 (13.1 percent) had anemia; and 15,959 (49.5 percent) had microalbuminuria. A total of 1,835 (4.9 percent) had a history of heart attack, 1,336 (3.6 percent) had a history of stroke and 2,897 (7.8 percent) had a self-reported history of heart attack or stroke.

Each of the three variables-anemia, microalbuminuria and low eGFR-was associated with cardiovascular disease. More than one-fourth of the patients who had all three kidney disease measures had cardiovascular disease, and their survival rates over the course of the study were lower by approximately 93 percent than those of any other group.

"These data suggest that screening for cardiovascular disease would be of high yield among patients with these risk markers but who do not report any history of cardiovascular disease symptoms," the authors conclude.

In a related study, Essam F. Elsayed, M.D., of Tufts-New England Medical Center, Boston, and colleagues evaluated a total of 13,826 individuals (average age 57.6) who had participated in one of two large cardiovascular health studies. Participants were recruited to the studies between 1987 and 1990 and followed up at approximately three-year intervals for an average of 9.3 years. At the beginning of the study and at each subsequent visit, blood creatinine levels were measured and used to track the decline in kidney function and the development of kidney disease both directly and by calculating eGFR. History of cardiovascular disease, as well as medication use, lifestyle characteristics, and other variables also were collected at the initial assessment.

At the beginning of the studies, 1,787 (12.9 percent) of the participants had cardiovascular disease. As measured by creatinine levels, 520 individuals (3.8 percent) experienced a decline in kidney function-including 128 (7.2 percent) of those with cardiovascular disease and 392 (3.3 percent) of those without cardiovascular disease-and 314 (2.3 percent) developed kidney disease. The presence of cardiovascular disease at the beginning of the study was associated with a decline in kidney function and the development of kidney disease as measured by both creatinine levels and eGFR.

"Our study demonstrates that cardiovascular disease is associated with subsequent kidney function decline and development of kidney disease," the authors conclude. "Because these patients are mainly under the care of primary care physicians and cardiologists, it is important to draw attention to the increased risk of kidney disease in this population, with goals of preventing further progression, managing sequelae of kidney disease as they arise and adequately preparing individuals for kidney failure with timely nephrology referrals. Only with recognition of risk factors for kidney disease can this happen."