What happens to your body when you face high levels of creatinine in the blood? Creatinine is a by-product of protein-type creatine. In other words, it is a waste that healthy kidneys filter every day. Muscle mass determines the normal levels of creatinine in men and women. The average percentage of filtering waste is 4% based on metabolic activities performed by the body. Usually, the kidneys filter this waste properly when they are healthy but as they come into contact with kidney disease; They cannot filter the blood properly resulting in high creatinine levels.