Serum creatinine, also called blood creatinine, is a product of human muscle metabolism. In muscle, creatine is formed slowly mainly through an irreversible non-enzymatic dehydration reaction and then released into the blood to be excreted in the urine. Therefore, blood creatinine is closely related to the total amount of muscle in the body and is not easily affected by diet. Creatinine is a small molecule that can be filtered through the glomerulus and is rarely absorbed in the renal tubules. Almost all of the creatinine produced in the body daily is excreted in the urine and is generally not affected by urine volume. Clinical testing of creatinine is one of the main methods to understand kidney function and is an important indicator to assess kidney function. Elevated serum creatinine implies impairment of kidney function.