Will thc show up on a routine pre-surgical blood test?

No: They must test for it specifically or run a routine drug screen. Many times for surgery they will do this.

THC: Pre-surgical blood tests do not test for thc. If you are having surgery let the anesthesiologist know if you use thc - dangerous issues arise when under if you use any illicit/illegal substance.

Wouldn't think so: In most states you must sign a specific consent for any drug test unless it is an obvious part of a pre-employment physical. Pre-surgical tests are done basically to prove your blood shows no signs of a hidden problem and you are not at extra risk from the surgery.