Final answer:
The primary care provider should wait until Karen's mother is present for the exam, as Karen is under 15 and legal consent from the guardian is necessary.
Step-by-step explanation:
When a twelve-year-old patient like Karen arrives for a Texas Health Steps preventive medical checkup without a parent, but with an older sibling, a primary care provider should handle the situation by following legal and ethical guidelines pertaining to consent and confidentiality. Patient privacy is vital, especially with minors, and adolescents may require confidentiality when discussing sensitive topics such as sexual health. The correct approach would be for the provider to ask the office staff to inform the mother that she must be present for the exam, as Karen is younger than 15 years old. The checkup should not begin until Karen's mother is present, to ensure legal guardianship consent and to discuss any findings or health concerns.