Can a doctor illegally test for drugs?

I believe the only circumstances for which a hospital or ER would call the police is:

• If you have illegal drugs IN your possession on their property, or
• If you are threatening /combative, attempting to harm staff.
• If you assault a staff person.
• If your records are requested under warrant because you were arrested for a crime that somehow relates to your hospital admission. For example, you committed a hit/run in your truck; the police tracked you down; they want the blood testing to prove you were DUI by drug use.

Your current/past medical history should still be private under HIPAA-- unless there's reason for the police to be involved. I'm just thinking out loud-- Can you imagine if hospitals had to call the police everytime a person was high on weed or publicly intoxicated in the ER--- they'd be on the phone all day!