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.