Creatine dietary sources

The serum creatinine concentration is dependent on the input function, or formation rate, and output function, or elimination rate. Its formation rate depends on the zero-order production from creatine metabolism, as well as input from other sources such as dietary intake. Creatine metabolism is directly proportional to muscle mass therefore individuals with more muscle mass have a higher serum creatinine concentration at any given degree of kidney function than those with less muscle mass. Exercise is associated with an increase of approximately 10% in the serum creatinine concentration. As the result of minimal muscle mass patients who are cachectic will have very low serum creatinine concentrations, as do those with spinal cord injuries. " Elderly patients and those with poor nutrition may also have low serum creatinine concentrations (<1 mg/dL) secondary to decreased muscle mass. Other factors that influence the serum creatinine concentration include the dietary intake of creatine. During the cooking of meat, some creatine is converted to creatinine, which is rapidly absorbed following ingestion. 

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