A 20-year-old female comes to the physician because she has never had a perioD. She has no medical problems, has never had surgery, and takes no medications. Examination shows that she is a tall female with long extremities. She has normal size breasts, although the areolas are pale. She has little axillary hair. Pelvic examination is significant for scant pubic hair and a sho, blind- ended vaginal pouch. Which of the following is the most appropriate next step in the management of this patient?