A 16-year-old girl presents to her pediatrician for a routine physical. Her mother expresses concern that her daughter has not yet had her first menstrual period. The girl reports normal breast development and growth spurt. Physical exam reveals normal external female genitalia, breast Tanner stage IV, and axillary/pubic hair Tanner stage IV. Her height is at the 50th percentile for her age. What is the most appropriate initial diagnostic test?

The correct answer to the question "A 16-year-old girl presents to her pediatrician for a routine physical. Her mother expresses concern that her daughter has not yet had her first menstrual period. The girl reports normal breast development and growth spurt. Physical exam reveals normal external female genitalia, breast Tanner stage IV, and axillary/pubic hair Tanner stage IV. Her height is at the 50th percentile for her age. What is the most appropriate initial diagnostic test?" is Option B: Serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

The other options — A) Pelvic ultrasound, C) Karyotyping, D) Serum thyroid-stimulating hormone (TSH) and prolactin — are incorrect for this USMLE Exam Prep question. As explained above: This patient has primary amenorrhea with normal secondary sexual characteristics, indicating estrogen production. The next step is to assess the hypothalamic-pituitary-ovarian axis with FSH and LH le…