Here is some more information from the Department of Justice that states who is able to professionally interpret. Note that many hospitals use these same regulations. I always go into an interview by telling the employer that I am fully bilingual, however I am not qualified and will not do medical interpretation as it is unethical for me to do so. However, I will communicate basic questions/conversation, but explaining diseases/risks/benefits/ technical education - it is off limits.
Interpretation involves the immediate communication of meaning from one language (the source language) into another (the target language). An interpreter conveys meaning orally, while a translator conveys meaning from written text to written text. As a result, interpretation requires skills different from those needed for translation.
Interpreting is a complex task that combines several abilities beyond language competence in order to enable delivery of an effective professional interpretation in a given setting. Consequently, extreme care must be exercised in hiring interpreters and interpreting duties should be assigned to individuals within their performance level. Command of at least two languages is prerequisite to any interpreting task. The interpreter must be able to (1) comprehend two languages as spoken and written (if the language has a script), (2) speak both of these languages, and (3) choose an expression in the target language that fully conveys and best matches the meaning of the source language.
From the standpoint of the user, a successful interpretation is one that faithfully and accurately conveys the meaning of the source language orally, reflecting the style, register, and cultural context of the source message, without omissions, additions or embellishments on the part of the interpreter.
Professional interpreters and translators are subject to specific codes of conduct and should be well-trained in the skills, ethics, and subject-matter language. Those utilizing the services of interpreters and translators should request information about certification, assessments taken, qualifications, experience, and training. Quality of interpretation should be a focus of concern for all recipients.
Many court systems have adopted assessments, certification or other qualification procedures to ensure quality, so when hiring an interpreter, whether for courtroom or other assignments, such competency measures should be taken into consideration. Interpreters can be physically present, or, if appropriate, may appear via videoconferencing or telephonically. When videoconferencing or telephonic interpretation are used, options include connecting directly to a specific professional interpreter with known qualifications, or opting to use a company providing telephonic interpretation services, preferably one with quality control safeguards in place.
In many circumstances, using a professional interpreter or translator will be both necessary and preferred. However, if bilingual staff are asked to interpret or translate, they should be qualified to do so. Assessment of ability, training on interpreter ethics and standards, and clear policies that delineate appropriate use of bilingual staff, staff or contract interpreters and translators, will help ensure quality and effective use of resources.