The answer to this question depends upon the length and complexity of the conversation the Deaf person will be having with the health care professional.
For example, if the doctor will be discussing whether to have major surgery, an interpreter would certainly be necessary to ensure effective communication. On the other hand, if the conversation is about visiting the doctor's office solely for a simple blood test, an interpreter might not be necessary. Instead, the individuals may be able to communicate effectively by, for example, writing notes or taking turns at a computer terminal.