My question concerns the use of creatinine, measured in the blood, as an indicator of kidney disease. My understanding is the normal range for the general population is between .8 to 1.2 as regards creatinine in the blood. Is the range different for body builders? Specifically, people who eat a great deal of protein daily, carry more muscle than most people, and work out heavily several times a week. I read that certain individual factors bump the range higher for people who have more muscle, people who eat a lot of protien, people who work out frequently (therefore likely worked out an hour or two prior to the blood test).

Yes, the serum creatinine has an inverse correlation with kidney function (the higher the serum creatinine, the lower the estimated glomerular filtration rate). There is a direct correlation of the serum creatinine with muscle mass (the greater the muscle mass, the higher the serum creatinine). In addition, about 10% of your serum creatinine may reflect animal meat that you have eaten in the past 24 hours. While physical exercise does not directly increase the serum creatinine, if this exercise is associated with sweating and volume loss, this could lead to some mild dehydration, which would result in an slight elevation of the serum creatinine.

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