Ordering labs on drug abusers

PalMD poses a really interesting question regarding the medical ethics of running lab tests on a patient to determine if they are drunk:

So here’s a non-life-and-death question: if a patient comes to see you and smells of alcohol, can you add an alcohol level to their blood work without specifically informing them?

As he points out, patients sign a generalized consent for treatment and generally do not expect to micromanage their doctor’s recommendations for tests that need to be run. I would imagine that doctors hardly ever inform their patients, item by item, what will be run on basic blood chemistry and immune panels. I would similarly imagine that should the doctor decide on a followup or two after some initial results s/he might just run them first and tell the patient later if it was a significant health issue.
So why not add a BAL (Blood Alcohol Level; a description of measurements including the familiar blood-alcohol concentration of legal importance) if you suspect a patient has been drinking?

And for that matter, why not order up a test for THC, MDMA, Meth, Cocaine……etc?
PalMD has a few more thoughts on
immediate risk:

What if I suspect the patient is intoxicated, but they leave my office and drive into a kindergarten?

Does the doctor have any obligation in this situation different, say, from the bank teller or store clerk? I think not. Scope of obligation is just too broad and the verification is correspondingly unnecessary if you are going to assert a requirement. If the doctor is obligated to act, s/he should probably just notify the security guard that if the patient appears to be getting into the drivers seat in the hospital parking garage/lot they should be detained.
additional scenarios:

Is EtOH level different from other tests? If so, how?…What is the purpose of the test?…Is deception involved, and if so, did it serve a purpose congruent with the patient’s needs?

EtOH is not different from the other tests but let us not be silly here. We know for dang sure the vast majority of patients are going to view it this way. Can you order up an HIV or other infectious disease test without consent? At least in those cases you can assert a communicable-disease public health concern. EtOH? Not so much.
knowledge of a drinking problem?

Let’s say a patient comes to see you. You know they have a history of drinking. They tell you they’ve quit. They don’t appear visibly impaired. You’ve drawn blood for other reasons (cholesterol, etc.).
After the patient leaves, a staff member says that the patient smelled a little soused. At that point, would it be ethical to add an ethanol level to the labs?

So this is the point where it gets pretty interesting to me. I think that the doctor is completely justified in inquiring about drug use if s/he suspects a potential dependence problem. It is no different than anything else the doctor happens to notice in the way of physical, physiological or behavioral irregularities that may indicate a treatable medical concern. However I suspect not every patient sees it that way, given the rather substantial difference in the way many people view having cancer and having a mental disorder.
On this basis, however, you have to ask what constitutes evidence of a problem. And here I think you have to parse pretty closely. Showing up to a doctor’s office appointment acutely intoxicated (on any substance) is probably a halfway decent (not exclusive, just decent) indicator of a control problem. But this can be observed. Is is relevant exactly how drunk the patient is? Probably not. So running the BAL lab is probably not called for just to verify that they seem impaired. Similarly, evidence of days-prior drug use (which you could get with certain compounds in a blood or urine test; many days from a hair screen if so inclined) is not a good indicator of medically-relevant drug use patterns.