A 33-year-old woman presents to your office because of abnormal hair growth. She has noticed gradually increasing coarse hair on her upper lip, chin, and lower abdomen for the past 3 years. She notices mild facial acne but denies frontal balding or deepening of voice. Her menses are irregular, occurring every 28 to 60 days. She and her husband use condoms for contraception. They have no children. She uses over-the-counter benzoyl peroxide for the acne but otherwise takes no medications or supplements. On examination, her BMI is 29.0 and her waist circumference is 36 in. Her voice is normal; she has mild facial acne. There is mild acanthosis nigricans of the axillae. Pelvic examination is normal without ovarian mass or clitoromegaly. Evaluation of her hirsutism should include which of the following?