A 29-year-old man being evaluated for primary infertility has azoospermia confirmed on two semen analyses. Both testes measure 16 mL with normal consistency. Serum FSH is 3.2 mIU/mL, LH 4.0 mIU/mL, testosterone 550 ng/dL. The MOST likely diagnosis is:

• A Obstructive azoospermia ✓
• B Klinefelter syndrome (47,XXY)
• C Sertoli cell-only syndrome
• D Complete spermatogenic maturation arrest

Explanation

Normal testicular volume with a normal FSH indicates intact spermatogenesis, so absent sperm in the ejaculate points to ductal obstruction (congenital bilateral absence of the vas deferens, epididymal block, or iatrogenic injury). In non-obstructive azoospermia such as Sertoli cell-only syndrome or Klinefelter syndrome, impaired spermatogenesis drives FSH elevation and the testes are small and soft. This FSH plus testicular volume pairing is the classic discriminator tested in exams.

Reference: Campbell-Walsh Urology, 12th ed.

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Written and medically reviewed by the StethoPrep medical team.