Creatinine is a chemical waste molecule that is generated from muscle metabolism. Creatinine is produced from creatine, a molecule of major importance for energy production in muscles. Approximately 2% of the body's creatine is converted to creatinine every day. Creatinine is transported through the bloodstream to the kidneys. The kidneys filter out most of the creatinine and dispose of it in the urine.Because the muscle mass in the body is relatively constant from day to day, the creatinine level in the blood normally remains essentially unchanged on a daily basis.

I dont know what cretanine is.
If it is found in large quantities in the blood test, it can damage the kidneys.
Sometimes irreversibly

Best answer is choosen as it is the best answer.