Yes. Every adult* should give serious thought to having and maintaining this important document. Establishing advance directives regarding future healthcare decisions can ensure that your wishes are met and can also relieve your family members of the stress of having to make difficult decisions for you.
Always carry a copy of your personal DPA/Advance Directive with you, and make sure that your "attorney in fact" also has a copy. This is especially important if you are not able to make your wishes known when you enter a hospital. Your Durable Power of Attorney for Healthcare is about more than whether or not you will accept a blood transfusion.
Individuals who are Jehovah's Witnesses can obtain a Durable Power of Attorney for Healthcare form from their local congregation.
*Pennsylvania code, Act 169, stipulates that in order to execute a health-care power of attorney, an individual must be at least 18 years of age, or be married, or a high school graduate, or an emancipated minor.