Creatinine

Urinary, strongly alkaline metabolic product that irreversibly develops in muscle tissue. The plasma level is 1.07 mg/dl. Excretion with urine is fairly constant (1.0-1.5 g/24 h).

Creatinine is a muscular metabolic end product. It's the decomposition product of creatine. This occurs in the muscles of the human being. It is a substance that can store energy and can be released again when needed (muscle work). Approx. 1-2% of the muscle creatine is broken down to creatinine per day. Creatinine - as far as known - has no function and is therefore waste. Since creatinine is excreted almost exclusively via the kidneys, serum creatinine is a sensitive parameter for filtration performance of the kidney. It is often determined by default during blood tests. In addition, serum creatinine levels can be used to monitor drug therapies with potentially harmful effects on the kidneys.

https://de.wikipedia.org/wiki/Kreatinin _{(Wikipedia CC-by-sa-3.0)}