Creatine in the body
The body of an average adult stores approximately 80–130 g of creatine. Creatine and its active form, creatine phosphate, play a crucial role in storing and providing energy for cells. By eating a balanced diet, the body obtains about half of its creatine requirements directly through food. The rest is produced by the body itself. An average man between 20 and 40 years old will synthesize about one gram of creatine per day. In women, the value is somewhat lower than for men. In both men and women, creatine synthesis decreases with age.
Creatine blood levels
Creatine is not only found in the cells but also in the blood. However, the creatine blood level is usually not used for diagnostic purposes.
Typical levels are:
Creatinine blood serum
Adults: 0.3–0.7 mg/dL (23–53 micromol/L)
Creatinine urine (24 h collection)
Men: 15–189 mg/d
Women: 19–270 mg/d
Creatine and creatinine
Although it does have its limits, the body does break down creatine into the byproduct creatinine at a rate of approximately two to three grams per day. It excretes the excess into the urine. Because the names creatine and creatinine are very similar, the two terms are often confused. While the creatine blood level usually has no diagnostic significance, creatinine is used as a routine parameter for determining renal function.