When Cardiovascular Disease is Suspected, Evaluate Kidneys, Too

DALLAS, Aug. 8 -- For patients with cardiovascular disease, chronic kidney disease is often a fellow traveler, necessitating more sensitive diagnostic tools that serum creatinine alone.

In an American Heart Association advisory statement published online today in Circulation, the cardiologists recommended that physicians go beyond serum creatinine to evaluate kidney function. They should also use the Modification of Diet in Renal Disease equation and the albumin-to-creatinine ratio, the AHA said.

"Many people use the serum creatinine," said Frank C. Brosius III, M.D., of the University of Michigan in Ann Arbor, and colleagues. "If their patients are with in the 'normal range' then they don't recognize that that their kidney function is decreased."

Chronic kidney disease is a risk factor for cardiovascular disease, and recent studies have confirmed that even early stages of renal dysfunction significantly increase the risk of cardiovascular events and death, the AHA statement said. In addition, treatment regimens are available to delay the progression of chronic kidney disease and manage its complications such as anemia and bone disease.

An estimated 11% of U.S. adults, about 20 million people, have chronic kidney disease.

Serum creatinine measurements alone fail to account for differences between individuals, particularly those with less muscle mass including older, smaller people and women, Dr. Brosius said. Physicians should use a single urine test to check albumin levels.

The Modification of Diet in Renal Function equation calculates glomerular filtration rate, which is the most accurate index of kidney function, using the serum creatinine and albumin levels, age, gender, blood urea nitrogen and whether the patient is black.

This equation "is currently the best validated method to estimate [glomerular filtration rate] for adults in the typical office setting," Dr. Brosius and colleagues wrote.

Online calculators for this formula are available to physicians, and groups such as the National Kidney Foundation and the American Society of Nephrology are encouraging laboratories to report kidney function using the equation on test result reports.

For all adults with cardiovascular disease, including coronary artery disease, congestive heart failure, and risk factors such as diabetes and hypertension, the American Heart Association statement recommends the following screening for chronic kidney disease:

• Measure serum creatinine and calculate estimated glomerular filtration rate using the Modification of Diet in Renal Function equation, and repeat in three months if the rate is less than 60 mL per minute^-1 times 1.73 m^-2.
• Measure the albumin-to-creatinine ratio with a random, or "spot," urine test, and repeat in three months if the ratio is more than 30 mg albumin per g of creatinine.

If either test is still positive after three months, the patient is considered to have chronic kidney disease. If both tests are negative, they should be repeated annually.

The statement recommended referral to a nephrologist for patients who have an estimated glomerular filtration rate less than 30 mL per minute^-1 times 1.73 m^-2 or a rate that rapidly decreases between repeat tests, or those who have a urinary albumin-to-creatinine greater than 300 mg albumin per g of creatinine.

Dr. Brosius said finding the presence of chronic kidney disease may change the treatment intensity and monitoring strategy as well as the use of agents required for the management of renal disease. Both the frequency of cardiovascular complications and the progression of chronic kidney disease can be ameliorated in these patients by appropriate intervention.