Creatine is a substance that is mainly found in the muscles; it is stored for use when the muscles need energy. Made by the cells from three amino acids, it is ultimately changed to creatinine and sent to the kidneys, as creatinine is primarily excreted as part of the urine. In renal failure, the kidneys cannot perform all of their normal functions, and creatinine accumulates.
What Is Creatine?
The cells make creatine from the amino acids glycine, arginine and methionine. Primarily found in the muscle, some creatine is also found in the nervous tissue, according to Gerhard Meisenberg, Ph.D., of the department of biochemistry at Ross University School of Medicine. The muscle cells then use the enzyme creatine kinase to form creatine phosphate and also use this enzyme to go from creatine phosphate back to creatine.
Function of Creatine
The cells make creatine, then change it to creatine phosphate, which is broken down to creatinine. As explained in "Principles of Medical Biochemistry" by Gerhard Meisenberg, Ph.D., the phosphate in creatine phosphate is full of energy. When the muscles are resting, most of the creatine is in creatine phosphate but when the muscles contract, the cells use the creatine kinase enzyme to make the energy that they need, especially during the first few seconds of a contraction. The muscles release creatinine, which is carried to the kidneys and excreted in the urine.
Creatinine and Renal Failure
When the cells break down protein, one product the process creates is ammonia; and because ammonia is toxic, the liver changes it to urea, then sends urea to the kidneys to be excreted in the urine. The creatinine released by the muscles is sent to the kidneys. In patients with kidney failure, the kidneys do not excrete as they should, and urea as well as creatinine accumulate in the bloodstream, explains James McMillan, M.D., chief of nephrology at the V.A. Loma Linda Healthcare System in "The Merck Manual for Healthcare Professionals."
Creatinine and the Diagnosis of Renal Failure
There are several tests that a physician will order when renal failure is suspected, including a urinalysis, a check for levels of albumin, electrolytes, uric acid, BUN or blood urea nitrogen, and creatinine. The physician may also order imaging tests to check for any abnormal blood vessels, blockage, cysts, masses and size abnormalities. Since creatinine is broken down and released by the muscles, it reflects the amount of muscle a person has. Therefore, the normal value for an adult ranges from 0.6 to 1.2 mg/dL, writes Diana Nicoll, M.D., Ph.D., associate dean of the University of California at San Francisco in the "Pocket Guide to Diagnostic Tests."
http://www.livestrong.com/article/387239-creatine-renal-failure/
