Creatinine is a waste product generated from muscle metabolism. It is produced at a relatively constant rate, primarily from the breakdown of creatine phosphate in muscles, an energy storage molecule. Creatinine is filtered from the blood by the kidneys and excreted in urine. As such, blood creatinine levels are a key indicator of kidney function. When kidney function is impaired, creatinine may accumulate in the blood due to reduced filtration efficiency. Testing creatinine levels provides valuable insight into the kidneys' ability to remove waste products from the body.
Creatinine
Muscle byproduct — first-line kidney marker.