depends on your context:
if you're talking about patients' anxieties when confronting medical staff (e.g. increased blood pressure readings), you'd call that "white-coat-syndrome".
But generally, "lab coat" is fine.

Most previous studies have focused on white coats. Two Australian studies showed that 36-59% of patients thought that junior doctors should wear white coats. Reasons given included professionalism, identification, and hygiene, yet white coats may be a source of, rather than a barrier to, cross infection. [...]
Although previous studies have shown that patients prefer doctors to wear white coats, we found that patients prefer a semiformal style of dress over formal suits and white coats. In line with previous studies, casual dress styles were less popular. This finding, and the association with age, suggests the beginnings of a trend away from patients preferring white coats. In general, patients prefer more conservative items of clothing.

aus: BMJ 2005;331:1524-1527 (24 December), Judging a book by its cover: descriptive survey of patients' preferences for doctors' appearance and mode of address. Marianne M Lill, Tim J Wilkinson

[OT]@laalaa: Klar, Freunde :-)

<On Topic> Ich habe keine persönliche Erfahrung mit Arztkitteln im englischsprachigen Raum, habe aber schon öfter "white coat" gelesen. Der Artikel oben ist von Neuseeländern geschrieben.
@laalaa und Helmi: Würde ein Allgemeinmediziner oder Hautarzt wirklich von seinem "lab coat" sprechen, auch wenn es bei ihm kein Labor gibt?

@ Mattes
Since the days of GP's in white coats are well and truly over, the wearing of "white coats" for physicians is now more or less restricted to hospitals (which do have labs!). I guess both is understood, but you probably wouldn't say "Where's my white coat?" as a doctor.

@ Mattes , they would certainly do that. But then more and more physicians dispense with those coats altogether, in their offices of course.

Thanks to both of you.