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.
Valium is the most addicting of these and is not used often for this reason. Xanax is very popular and is prescribed often for tinnitus. However, the ATA report on medications that cause tinnitus lists Xanax as causing it in 6.6% of cases. For this reason I am not a fan of Xanax. A slower acting and somewhat less addicting medication is Klonopin. It takes longer to become dependent on Klonopin and it does not cause tinnitus.