An interpreter interprets spoken words, whereas a translator translates written words. This distinction is important because if you are seeking out services for your patient, you’ll get an entirely different skillset from a translator than you would from an interpreter!
That being said, interpreters should be versed in translation, but likely will not be to the extent of a professional translator. Interpreters often have to do what is called <em>sight translation</em>, which is reading aloud a document from one language into another. For example: many times I am presented with English forms for my Spanish-speaking patients, and will read those forms aloud in Spanish.
A professional translator often has a series of specialties in which they are well-versed and can translate. A translator likely cannot translate ALL types of documents, just as an interpreter cannot interpret for ALL types of interactions.