Like I said, it depends on the state.

For Cali...

http://www.endabuse.org/userfiles/fi...tory_calif.pdf

California Mandatory Reporting Law: A Summary
‡
WHEN REQUIRED TO REPORT:
Any health practitioner employed in a health facility, clinic, physician’s office, local or
state public health department, or clinic or other facility operated by a local or state public
health department, is required to make a report if he or she “provides medical services for a
physical condition to a patient whom he or she knows or reasonably suspects is”:
(1) “suffering from any wound or other physical injury inflicted by his or her own act
or inflicted by another where the injury is by means of a firearm”, and/or
(2) “suffering from any wound or other physical injury inflicted upon the person
where the injury is the result of assaultive or abusive conduct.”
“Assaultive or abusive conduct” is defined to include a list of 24 criminal offenses,
among which are murder, manslaughter, torture, battery, sexual battery, incest, assault with a
deadly weapon, rape, spousal rape, abuse of spouse or cohabitant, and an attempt to commit
any of these crimes.
It's going to depend on the medical practitioner, as well as the extent of the injury. Find someone who's more liberal and not an abusive relationship zealot, you'll probably be just fine. Find someone who's conservative and over sensitive about abusive relationships, you'll probably run into trouble.