Even a small loss of kidney function significantly increases the risk of cardiovascular disease and death, so clinicians may assess kidney function values, such as creatinine and glomerular filtration rate (GFR), to gauge a patient's risk of heart disease. According to a large new study, serum levels of cystatin C may be a better indicator of renal function and cardiovascular risk than creatinine or GFR.

Researchers compared creatinine and cystatin C levels in 4,637 elderly patients living in the community. Participants were tested in 1992 and 1993 and followed until 2001. The researchers determined how well test values predicted death from all causes, death from cardiovascular causes, and incidence of heart attack and stroke. They found that the 20% of participants with the highest levels of cystatin C had twice the risk of death from all causes and from cardiovascular disease, and a 50% higher risk of heart attack and stroke, compared with those with the lowest level of cystatin C. In contrast, creatinine levels identified a smaller high-risk group, and all others appeared to have only an average risk.

Like creatinine, cystatin C is a protein normally cleared by the kidneys; poor kidney function allows these proteins to accumulate in the blood. But levels of creatinine, a breakdown product of muscle, are influenced by individual factors such as age, race, sex, and lean muscle mass. Cystatin C, which is produced by nearly all human cells and excreted into the bloodstream, appears to be independent of these factors. Rising cystatin C levels may reliably reflect moderate kidney disease earlier than creatinine levels, allowing clinicians to identify and treat patients at high risk for cardiovascular disease sooner.

Although the cystatin C test has been approved for diagnostic use by the Food and Drug Administration, it's not yet widely available in clinical settings.

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