Who Can Be Subpoenaed to Trial
For cases in Tennessee state courts, Tenn. Code Ann. sec. 24-9-101 sets out the persons who cannot be subpoenaed to trial, and subsec. (6) includes practicing physicians, psychologists, senior psychological examiners, chiropractors, and dentists. If the person cannot be subpoenaed to trial, they are unavailable and their testimony is likely subject to the "former testimony" hearsay exception at Tenn. R. Evid. 804(b)(1) and Tenn. R. Civ. P. 32.01(3). Anyone else is generally available to be subpoenaed if in the geographic range of the Court, and the former testimony exception will not apply unless there is a separate basis for it.
In Federal court, on the other hand, Tenn. Code Ann. sec. 24-9-101 does not apply. Health care providers' hearsay testimony will likely not come into evidence unless they are immune from subpoena for another reason.