What is a formal document that indicates a patient's decisions about future medical treatment called?

The correct answer is an advance directive. This type of document is specifically designed to communicate a patient's preferences regarding medical treatment in the event they become incapable of making decisions for themselves. It serves as a legal document that provides guidance to healthcare providers and loved ones about what actions to take concerning medical interventions, resuscitation efforts, and other critical healthcare decisions, ensuring that the patient’s wishes are respected.

While a living will is also related to this context, it is a specific type of advance directive that typically focuses on end-of-life treatment decisions. An advance directive may encompass a living will but can also include any other wishes regarding medical treatment, making it a broader and more inclusive term.

A medical record is a comprehensive collection of a patient's health history and treatments but does not specifically capture their future treatment preferences. Power of attorney refers to a legal document that designates someone to make decisions on behalf of another person, which may include medical decisions but does not directly specify the patient's treatment preferences. Therefore, the advance directive is the most appropriate term for a formal document indicating a patient's decisions about future medical treatment.