Review Question - QID 212728

A 16-year-old boy comes to his primary care clinic for a sports physical. He states that he wants to try out for his high school’s football team this year. He's "trying to get in better shape.” The patient has no complaints except for occasional headaches when he is stressed about exams. The patient also mentions that he is embarrassed of his “small penis” and asks if there is something he can take for that. The patient’s temperature is 98°F (36.7°C), blood pressure is 118/76 mmHg, and pulse is 79/min. On physical examination, the patient is obese and has no visible facial hair. His testes are less than 20 mL in volume, and his phallus measures less than 8 cm. Initial labs show testosterone levels of 95 ng/dL and a low follicle stimulating hormone/luteinizing hormone ratio. Which of the following is the next best diagnostic step?