Question

A 58-year-old man presents to the primary care clinic reporting a 9-month history of progressive fatigue, decreased libido, and erectile dysfunction. He has no headaches, visual changes, or prior testicular trauma. His vital signs show a blood pressure of $128/82 \text{ mmHg}$, heart rate of $74 \text{ /min}$, and respiratory rate of $14 \text{ /min}$. His body mass index (BMI) is $34 \text{ kg/m}^2$. Physical examination reveals normal visual fields, no gynecomastia, and bilaterally descended testes with a slightly soft consistency and a volume of $12 \text{ mL}$ bilaterally (normal: $15-25 \text{ mL}$). The physician suspects male hypogonadism and initiates a stepwise laboratory evaluation.

Based on Endocrine Society guidelines, arrange the following laboratory investigations in the most appropriate chronological sequence for establishing the diagnosis and etiology. Assume each subsequent test is pursued only after the preceding test results confirm the need for further evaluation.