A biomarker called cystatin C, which measures kidney function, predicts which people are less likely to survive a heart attack, according to research published in Circulation: Journal of the American Heart Association.
In the study, patients with the highest levels of cystatin C in their blood after they had a type of heart attack called non-ST-elevation acute coronary syndrome (ACS), had “a more than 55 percent cumulative probability of death versus about a 7 percent probability of death among patients with lowest levels of cystatin C,” said lead author Tomas Jernberg, M.D., Ph.D., an associate professor at Uppsala Research Center in Sweden.
It is the first study to demonstrate that cystatin C can be used as a quick and early predictor of death, he said.
Cystatin C is a cysteine protease inhibitor filtered through the kidneys and circulated in the blood. Kidney function is one of several factors used to determine which heart attack patients need aggressive treatment to reduce the risk of death or a non-fatal second heart attack. Currently, physicians calculate kidney function by measuring creatinine, which is another biomarker excreted by the kidneys. But creatinine levels are calculated using a complicated formula that is based on age, gender and weight. On average, the circulating cystatin C level averages 1.00 milligrams per liter (mg/L), and risk increases as the level increases.
Compared to creatinine, “cystatin C is a lot more practical because it doesn’t require these additional calculations. An increased level is associated with increased risk regardless of age, gender or weight,” he said.
The study analyzed blood from 726 patients who were admitted to the hospital with heart attack symptoms between March 1997 and February 1998. Three hundred and eighty of these patients had non-ST-elevation acute coronary syndrome. Sixty-one of these patients underwent procedures such as balloon angioplasty during their initial hospitalization, and 88 had similar procedures within 30 days of the initial hospitalization.
Dividing the patients into four groups, cystatin C levels ranged from a low of 0.83 mg/L to levels of more 1.24 mg/L or higher in group 4. The relative risk of death was 1.8 in group 2; 3.2 in group 3 and 11.7 in group 4. After adjusting for other risk factors, the level of cystatin C remained an independent predictor of death, Jernberg said.
“Early risk stratification of patients with suspected or confirmed non–ST-elevation ACS is essential. Estimation of renal function by measuring creatinine and calculating creatinine clearance has emerged as an important part in this process. The present study strongly suggests that measuring plasma cystatin C not only is more practical at bedside by making complicated calculations unnecessary, but also will substantially improve the early assessment of these patients,” the authors concluded.
Researchers noted that this marker was unable to predict the risk of future coronary event.
Co-authors are Bentil Lindahl, M.D., Ph.D.; Stefan James, M.D., Ph.D.; Anders Larsson, M.D., Ph.D.; Lars-Olaf Hansson, M.D., Ph.D.; and Lars Wallentin, M.D. Ph.D.