Which of the following is considered a PHI identifier?

All the options provided—Social Security number, date of birth, and medical record number—are considered identifiers of Protected Health Information (PHI) under the Health Insurance Portability and Accountability Act (HIPAA).

The Social Security number is a unique identifier that can directly link to an individual’s identity and personal information, making it a clear component of PHI when it is associated with health data.

The date of birth is also considered an identifier because it can be used to uniquely identify an individual, especially when combined with other data points. It is sensitive information that, in the context of health care, can lead to the identification of a patient.

The medical record number is specific to an individual's health record and is unique to the healthcare provider’s system. It directly ties to the patient's health information and is therefore classified as PHI.

Since all these identifiers can be used to distinguish one individual from another in a healthcare setting, the correct answer encompasses all three, which confirms that they are all considered PHI identifiers under HIPAA regulations.