How do you differentiate obstructive from non-obstructive azoospermia on initial evaluation?

• A. Obstructive: normal testicular size and normal or near-normal FSH with azoospermia due to ductal blockage.
• B. Non-obstructive: normal testicular size with elevated FSH.
• C. Obstructive: small testes and high FSH.
• D. Non-obstructive: large testes with low FSH.

Answer: (A)

Understanding whether azoospermia is obstructive or non-obstructive at first look relies on whether sperm production is preserved and how the testicles respond. In obstructive azoospermia, the testes produce sperm normally, but a blockage prevents it from reaching the ejaculate. Because production is intact, the testicular size is usually normal, and FSH is normal or near normal since the Sertoli cell feedback remains appropriate. In non-obstructive azoospermia, sperm production is impaired, so the testes often appear smaller or less consistent in size, and FSH tends to be elevated due to reduced inhibin B signaling from the testes. Therefore, a normal-sized testis with normal or near-normal FSH best fits obstructive azoospermia, while small testes with elevated FSH point toward non-obstructive azoospermia.