Chato,
What is happening for you to suspect they are bad? As lincolnnellie mentions, there is a minimum thickness for the rotor, and there should also be a runout to ensure that the surface is flat.
If you are getting a pulsation through the brake pedal under braking then it is time to turn or replace the rotors. There are any number of reasons why this could happen. But 34k is pretty low to swap out the rotors. Please describe your symptoms...
Bogatyr