Well done to Frequent SLF for finding that information tucked away, but I would think that it refers more to Red Cross flights, air ambulances etc ("medical transports") with premeditated requirements for expeditious handling, rather than a medical emergency on a 'normal' flight.

PAN PAN MEDICO/MAY-DEE-CAL has been looked at in the UK but the feeling seems to be that the aircraft making a straight PAN PAN call and including in the first call a brief statement of the problem will do the trick, and the MEDICO etc doesn't add anything to the picture, except another (superfluous) term and category.

Very interesting... We get a fair few "ambulance" and "medical emergency" flights into Heathrow and I've yet to hear one of the ambulance variety mention the word PAN. Flight plan info states "ambulance", or something similar, but half the time they are positioning flights with just a pilot aboard! A good number of commercial airline flights are also flagged as ambulance flights but never say anything on the R/T.