Question

A 31-year-old woman and her husband come to the office to undergo evaluation for primary infertility. They have engaged in regular, unprotected intercourse for the past 15 months without achieving pregnancy. The patient reports that her menstrual periods have always been unpredictable, occurring approximately every 7 to 9 weeks. She has also struggled with persistent acne and the growth of thick hair on her chin and lower abdomen over the last few years. She does not report any deepening of her voice, increased muscle mass, or abnormal bruising. Her body mass index is 32 kg/m². Vital signs are normal. Physical examination reveals moderate facial hirsutism, but no clitoromegaly or purple striae are noted. A urine pregnancy test is negative. The physician suspects polycystic ovary syndrome but notes that a diagnosis requires excluding other conditions with a similar presentation. Along with thyroid-stimulating hormone and prolactin, which of the following laboratory tests is most necessary to definitively exclude a common mimicker of this patient's suspected condition?