it's from high protein and weight training
copied from google source:........Elevated levels are sometimes seen in kidney disease due to the fact that a damaged kidney will not remove creatinine from the body as it should. Also, elevated levels are seen with the use of some drugs that could impair kidney filtration. Finally, elevated levels could also be seen with muscle degeneration, a high protein diet, or creatine supplementation.
With respect to creatinine measurements, it's important to note that the amount of creatinine in the blood is regulated by the amount being produced (from protein degradation - muscle or dietary) vs. the amount that's being removed (by the kidney).
Therefore, although creatinine in the blood could be a marker of a damaged kidney's inability to filter creatinine out of the body at a normal rate, it could also be a marker of rapid protein degradation (via muscle damage from weight training or from a high protein intake).
Think of the blood as a sink. If you turn on the faucet at a low rate, the amount of water going into the sink and the amount leaving the sink should balance each other out, leading to a predictable amount of water in the sink at any moment. However, if you partially plug the drain, you'll get more water accumulating in the sink at the same faucet flow rate.
This is similar to kidney dysfunction (thinking of the water as creatinine). However, alternatively, if the drain remains unplugged but you crank up the faucet flow rate, you'll get more water in the sink due to the higher flow. This is similar to a high protein diet.
Since weightlifters are continually breaking down muscle protein (this is a good thing), even in the absence of a high protein diet, blood creatinine concentrations tend to be elevated. Furthermore, add in a higher protein diet and creatinine concentrations in the blood will rise.
Finally, since creatinine is also a breakdown product of creatine, if a weightlifter is taking creatine supplements (which most do), blood creatinine concentrations will also be high. What all of this means is that the faucet is turned up in weightlifters, not that the drain is plugged.
To address the other relevant measure, the nitrogen component of urea, blood urea nitrogen (BUN), is the end product of protein metabolism and its concentration is also influenced by the rate of excretion (as is creatinine). Excessive protein intake, kidney damage, certain drugs, low fluid intake, intestinal bleeding, exercise, or heart failure can cause increases in BUN.
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