Science Moment

Creatine is an organic acid found in vertebrates that supplies energy to muscles. In humans, it is generated in the liver and derived from food sources (mainly meat & fish). During the first few seconds of exercise, the phosphorylated form of creatine is an immediate source of high energy phosphate groups to convert ADP to ATP.
About 2 grams of creatine is irreversibly converted to creatinine per day. Creatinine is then filtered out of the blood through the kidneys. If the kidneys are not functioning properly, blood creatinine levels are elevated.  A creatinine clearance test is used to detect abnormal renal function. This test compares levels of creatinine in the blood to levels excreted in urine over a 24-hour period.
Creatinine clearance appears to decrease with age & men typically have higher levels than women because they often have more skeletal muscle tissue. Normal adult levels of creatinine are between 0.7 - 1.4 mg/dl.