A creatinine level measures the level of creatinine in the blood, which is an indication of proper kidney function, states MedlinePlus. Creatinine is a waste product of creatine, which gives energy to the muscles. Because creatinine is excreted from the body by the kidneys, elevated levels indicate abnormal kidney function.
A creatinine level is measured by obtaining a blood sample. Creatinine levels generally become elevated due to a medical condition, such as a blocked urinary tract, kidney damage or infection, problems with blood flow to the kidneys and muscle problems, according to MedlinePlus. Low creatinine levels are usually a result of health conditions involving the muscles.