A 19-year-old boy is evaluated for tall stature, gynecomastia, small firm testes, and infertility. Karyotype is 47,XXY. Which laboratory finding is most characteristic of Klinefelter syndrome?

• A Low FSH, low LH, low testosterone
• B High FSH, high LH, low testosterone ✓
• C Normal FSH, normal LH, normal testosterone
• D Low FSH, low LH, high testosterone

Explanation

Klinefelter syndrome (47,XXY) causes primary testicular failure with seminiferous tubular hyalinization and Leydig cell dysfunction. Loss of negative feedback from testosterone and inhibin leads to elevated FSH and LH (hypergonadotropic hypogonadism) with low testosterone. Low gonadotropins with low testosterone would suggest a pituitary or hypothalamic cause (hypogonadotropic hypogonadism), which does not fit Klinefelter syndrome.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.