Can a New Blood Test Help Predict Who Is at Risk for Developing Heart Failure?

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The summary below is from the full report titled "Cystatin C Concentration as a Risk Factor for Heart Failure in Older Adults." It is in the 5 April 2005 issue of Annals of Internal Medicine (volume 142, pages 497-505). The authors are M.J. Sarnak, R. Katz, C.O. Stehman-Breen, L.F. Fried, N. Swords Jenny, B.M. Psaty, A.B. Newman, D. Siscovick, M.G. Shlipak, and the Cardiovascular Health Study.

What is the problem and what is known about it so far?

In heart failure, the heart cannot pump enough blood to supply the body's needs. Risk factors include high blood pressure and a previous heart attack. Low kidney function may also increase risk. The easiest way to detect low kidney function is to measure creatinine, a protein in the blood that increases when kidney function decreases. However, creatinine levels are not always accurate. Cystatin C is another protein in the blood that increases when kidney function decreases. It may be a more accurate measure of kidney function, but its role as a predictor of heart failure is unclear. If low kidney function increases a person's risk for developing heart failure, higher cystatin C levels might be a sign of that higher risk.

Why did the researchers do this particular study?

To see whether cystatin C levels in the blood predict a person's risk for developing heart failure.

Who was studied?

4384 people age 65 years or older from 4 areas in the United States. None had ever had heart failure. All were participants in the Cardiovascular Health Study, a research project begun in 1989 to identify risk factors for heart disease and stroke.

How was the study done?

The researchers took blood for creatinine and cystatin C testing at the beginning of the study. They contacted the participants periodically over the next 8 years to determine whether anyone developed heart failure. The researchers then compared the participants' risk for developing heart failure according to their creatinine and cystatin C levels.

What did the researchers find?

763 participants developed heart failure. Participants with higher cystatin C levels were more likely than those with lower levels to develop heart failure. Higher creatinine levels did not reliably predict participants' risk for heart failure.

What are the limitations of the study?

The findings do not reveal whether cystatin C is good at predicting different forms of heart failure. Cystatin C levels may increase for reasons unrelated to kidney function. Instruments that measure cystatin C are not widely available, so for now the test cannot be used widely.

What are the implications of the study?

Higher levels of cystatin C predict higher risk for heart failure. Cystatin C may also be a better test of kidney function than creatinine. The findings strengthen the impression that low kidney function is a risk factor for heart failure. However, use of cystatin C to measure kidney function and predict risk for heart failure is likely to be limited until the test becomes more widely available.