Due to the toxic effect of dyes on the kidneys, cardiologists routinely assess patients' kidney function prior to conducting a heart procedure.
Kidney function is commonly assessed by a standard blood test, which measures the amount of substance known as serum creatinine present within the blood. Serum creatinine is a waste product of the muscles of the body which, in a healthy individual, is filtered out of the body by the kidneys. Higher levels of serum creatinine in the blood indicate reduced functionality of a patient's kidneys.
The National Kidney Foundation defines the five stages of kidney disease. These stages are determined primarily by serum creatinine measures.