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.