Creatine is a compound, produced primarily by the liver. It is an energy source that is utilized for muscle contracts. Creatinine is a waste product of creatine, which is produced by the muscles and removed from the body by the kidneys.
As almost all creatinine is filtered from the blood by the kidneys, its blood levels are usually a good indicator of kidney functions. Its level depends on the muscle mass, therefore its levels are slightly higher in men than in women.