It`s an interesting question you raise. Preliminary queries relate to
your words 'psychiatrist','christian' and 'right'. Sidestepping such
areas however analytic custom seems to vary: where a mode of address is
used it often consists  of the title followed by the surname (eg Mr
Smith). A common alternative is use of a first or personal name followed
by the surname. Part of the issue relates surely to what the particular
useage means to the client at the particular time; what is his/her need
or phantasy? What wish or need is there for distance, familiarity, or
intimacy? What would the 'psychiatrist' be conveying:
dominance,superiority,status,a paternal role/countertransference,a wish
for regression,seduction,disrespect,
friendliness,warmth,equality....Also what is the psychic status of the
patient:the level of regression and it`s management can be a significant
influence.
The age of the client seems to influence custom with children being
addressed by first names and useage changing to more formal modes with
their increasing age (especially where the therapist is younger).
My own practice increasingly is ,where names are needed, to use the
persons title and surname. Conveying warmth I think comes about via
other means in the analytic relationship.
In communications about a client,eg in reports,papers,lectures,etc a
further layer of complexity gets added with the triangulation inherant
in such matters.  Reduction to a letter, eg Mr X, could provide
anonymity,or be dehumanising....There is a growing literature on the use
of case material and its potential for impingement.
I would be interested to hear others views on this topic.

Roger Willoughby(Folkestone,UK).