The production of natural creatine is a protein building block that is stored in your muscles and used as energy. When your kidneys are healthy, creatinine is safely removed from the body. The aim of normal creatinine levels in the blood should range between 0.6 to 1.2 mg/dL for men, and 0.5 to 1.1 mg/dL for women. Men are thought to have higher creatinine levels because they have greater muscle mass.