Creatinine is a breakdown product of protein molecules. It is formed in the muscles and then enters the bloodstream, from where its level is determined (by sampling venous blood). Creatinine is essential for energy metabolism in body tissues. The more muscle work, the more creatinine is released, because it is an energy product. In men, the reference values of creatinine levels are higher than in women, which is quite reasonable: there is more muscle mass and volume of physical activity in men than in the fairer sex. However, deviation of creatinine from the norm can be a signal of an illness in the body. So, an increased level of creatinine occurs in conditions such as: renal failure, dehydration, trauma to the bone and muscular systems, pregnancy, with toxic or mechanical damage to internal organs, after increased muscle load, with a high-protein diet. Reduced creatinine levels can be with: strict diets with the exclusion of protein foods, pregnancy.