Creatinine is a natural metabolite of creatine and creatine phosphate. If the body cannot use any more creatinine, the kidneys excrete it completely and do not modify it in the process. If the body gets more creatinine through foods (there are certain foods that are particularly rich in creatinine), it is absorbed by the body and excreted again in an unmodified manner. Creatinine does not really benefit the body but also doesn’t harm it either.
The creatinine level in the blood is generally used as an indicator of renal function. However, because the creatinine value can also increase depending on how much creatine is ingested and any increase in the size of the creatine pool in the body, dietary supplementation with creatine can be incorrectly though to negatively affect renal function. However, there is no scientific evidence supporting any form of renal damage from creatine or creatinine.