In the usa, at what age can a minor receive medical care without parental knowledge or consent?

Varies by state...: The rules vary by state, by disease or condition being treated, by legal status of the minor, etc... It can get confusing, so takes some online research in each state. Usually, conditions regarding reproduction (normal teen sexual issues) are private, as well as substance abuse (smoking, marijuana, alcohol), and mental health issues such as depression. The child can choose to involve the parents.