I was talking in generalities and specifically a reply to,
What happens if EMS gets dispatched to a 'flu like symptoms' call and the patient ends up signing out AMA (or ends up being a no transport due to no medical need in systems that allow it). If some sort of quick noninvasive test could be preformed, then EMS has the ability to add to public health statistics even though the patient isn't actually transported.
As far as TB skin test are concerned, a TB test (purified protein derivative) is an injection that gets checked for a reaction 48-72 hours following injection. It's not something that gets sent out to a lab. In this sense, it kinda of makes sense to have EMS administer it to at risk home bound populations since the prehospital provider has around a 24 hour period to return and check it at the patient's abode which could be worked around calls. Yes, it isn't something that should or could be done on a call, but even emergency physicians do a fair amount of primary care.
Again, I'll quote you.
You objected to not just EMT-Bs not doing a test due to lack of training, but also to anyone in EMS doing it because it isn't an emergency. How many emergencies could be prevented with proper care and monitoring?
The line between "lab-type tests" (which the PPD test is not) and field tests is constantly getting blurred. Examples include quick tests for
Troponin 1 or the ever mentioned
iSTAT point of care testing. I'm willing to bet money that within 10-15 years some sort of point of care blood testing will be as standard as a cardiac monitor or AED on ambulances.