Creatinine:

An end-product of protein metabolism found in the blood and urine, that can be used to help assess if the kidneys are working adequately. A related test, using simultaneous measurements of a timed urine sample plus a blood creatinine test, is called the creatinine clearance. 

Creatinine is a waste product of muscle metabolism. The blood concentration of Creatinine depends upon two things - the amount of muscle you have and the ability of your kidneys to excrete the Creatinine. The protein you consume does not affect it. High levels of Creatinine in the blood usually indicate deterioration in kidney function. High values require medical evaluation by your health care provider, especially when associated with high BUN results. Low values are not generally considered significant.

By-product of muscle activity normally removed from the blood by the kidneys. Normal blood level is 0.6-1.4 mgm%. When blood level is above normal, this indicates that kidney function is not normal. It is one of the main laboratory tests followed after a transplant to see how well the kidney is working.