Final answer:
A medical assistant should adhere to HIPAA guidelines and protect the patient's privacy by not disclosing medical information to unauthorized individuals, including a patient's sister-in-law, without explicit consent.
Step-by-step explanation:
The medical assistant should follow the Health Insurance Portability and Accountability Act (HIPAA) guidelines and protect the patient's privacy. They are not permitted to disclose medical information to anyone not authorized by the patient, including the patient's sister-in-law, unless the patient has given explicit consent for that individual to have access to their medical information. In such a situation, the medical assistant should politely inform the caller that they cannot share any information without the patient's consent and advise them to ask the patient directly.