Do crews look for "Dr." on a passenger manifest to identify medical doctors? With many airlines, when a passenger buys a ticket online, there is a space for them to select a "title", such as Ms., Mr., Dr., Rev., etc.    In most social circumstances, the title "Dr." is applicable to anyone with a doctoral degree (M.D., Ph.D., D.D., etc).

I have heard a rumor that in the event of a medical emergency on the plane, the cabin crew will check the passenger manifest for people who have given the title Dr., in hopes of finding a medical doctor who can assist.

As a consequence, goes the rumor, a passenger who has a doctoral degree, but is not a medical doctor (say, a PhD in mathematics), should not choose the title "Dr." when buying a ticket, since if there is a medical emergency, the cabin crew might waste time asking this mathematician for assistance.

I have also heard it said that this is nonsense, that crews would not bother looking at the manifest, and would simply make a PA announcement asking for anyone with medical training.  (This has the advantage that it would also identify medical professionals such as nurses, paramedics, etc., who would not use the title "Dr." anyway.)

Which of these reflects actual crew training or standard procedures?

What is the best practice for a passenger who holds a non-medical doctorate?  I've never seen any official guidance from an airline on when to use the title "Dr" on a ticket.

(I wasn't sure if this question would be best here, or on Travel.SE, or maybe even Skeptics.SE, but I thought this site would be most likely to have people with first-hand knowledge from the crew side.  I'm open to suggestions for migration.)
You are correct that it is done by PA rather than by reference to the manifest, at least at my carrier in my type of aircraft. As you surmise, the "Dr" notation has too many opportunities for both false positive AND false negative results to be where you want to start when time is of the essence.

Besides, if you need medical help at 40,000', you're probably much better off in the hands of a good E.R. nurse or paramedic than with a radiologist who hasn't done hands-on emergency care since his residency. 

Most airlines use a service that's reachd by a phone patch to an E.R. doctor who specializes in evaluating these sorts of situations (and recommending, divert now or continue on), so any medical professional on the aircraft is working under his direction. He is also familiar with the contents of a medical kit carried on the aircraft just for these situations, so he can say "have the (nurse/paramedic/doctor/etc) administer ___ out of the medical kit" already knowing what is &amp; isn't available.

Interestingly, a veterinarian can also administer the same medications the other medical professionals can in this sort of situation!