Insurance companies have a new loophole to get out of paying claims - that they weren't "pre-authorized." They can disallow up to 50% of what would be covered, which leaves you responsible.
Most procedures need to be pre-cert before the provider will schedule it. But, check, check, check yourself the day before you go in for anything, an x-ray, MRI, CATScan, angio, EKG, colonscopy, etc., and make sure that your doctor, surgeon, etc., has covered all of the bases with the insurance company. This way, YOU are sure that everything is hunky-dory with the insurance company and not relying on the doctor/surgeon's nurse saying, "oh yes, we did that." Maybe they didn't or didn't see it through to completion. It happens.
Being proactive about your coverage now goes hand in hand with being proactive about your health. They're one in the same.