From HcPro’s newsletter Briefings on HIPAA:
Q: I send patient reminders for annual examinations and follow-up appointments. Are postcards permissible or does this method disclose too much information? Must the information be inside a folded card or in a sealed envelope?
A: The nature of your practice determines what is appropriate. If you are sending appointment reminders for a general medical practice, a postcard reminder is acceptable as long as it does not contain any information about the specific type of appointment or reason for treatment. If the name of your practice or facility would provide information about a patient’s condition (e.g., XYZ Cancer Hospital or Community AIDS Clinic), send the reminder notice in an envelope to protect your patients’ privacy. The return address on the envelope should not include the name of the clinic or hospital in these situations.