Medical identity theft primarily involves the theft of which type of information?

Medical identity theft primarily involves the theft of a person's Health Insurance ID and Social Security Number because these pieces of information are critical in accessing and utilizing healthcare benefits. When an individual's Health Insurance ID is stolen, it can be used to receive medical services, medications, or even surgeries without the victim's knowledge or consent, leading to significant financial and personal repercussions. Additionally, the Social Security Number serves as a key identifier that can link to various personal details and financial accounts, further enabling thieves to exploit the victim’s identity across different domains.

The other options, while related to healthcare practices, do not directly pertain to the core of medical identity theft. Preferences for treatment, billing statements, and appointment records are more about the patient-provider relationship or healthcare operations rather than the core financial and personal information that facilitates identity theft.