Creatinine is a chemical waste product of creatine. Creatine is a chemical made by the body and is used to supply energy mainly to muscles.
A blood test that measures the level of creatinine in the blood is used to test kidney function. Creatinine is removed from the body entirely by the kidneys. If kidney function is not normal, creatinine level increases in your blood. This is because less creatinine is released through your urine.