Blood creatinine level. The blood creatinine level shows how well your kidneys are working. A high level may mean your kidneys are not working as they should. The amount of creatinine in the blood depends partly on the amount of muscle tissue you have.
Xanax is stronger. 0.5 mg of Xanax equals 10 mg of Valium. But Xanax is mostly effective for about 2 hours, then you may have to repeat the dose (and regular doses may cause addiction). Valium peak-level effects wear off after 1 hour, but it stays in blood longer, and continues working for about 12 hours.
One 10mg Valium is equivalent to a standard 0.50 mg dose of Xanax. Anyway, I have rambled on a bit more, but to answer your question, yes, Xanax does not stay in your body that long at all (48 hours, unless u have been taking more over a shorter period of time then it can build up a little bit and stay in the body longer).