Assessment of Patients' Competence to Consent to Treatment

A 75-year-old woman has type 2 diabetes mellitus, peripheral vascular disease, and a gangrenous ulcer of her left foot. A below-the-knee amputation is recommended, but she declines, saying that she has lived long enough and wants to die with her body intact. Her internist is concerned about her increasing confusion over the past year and notes that she appears to be depressed. How should her physician determine whether her decision is competent?