Which laboratory finding is typical in Klinefelter syndrome?

• A. 47XXY karyotype
• B. 46XY karyotype
• C. Elevated Testosterone
• D. Normal LH

Answer: (A)

Klinefelter syndrome is caused by an extra X chromosome in males, so the characteristic laboratory finding is a karyotype of 47XXY. This chromosomal pattern is what defines the condition and explains the downstream effects on gonadal function. With the extra X, the testes fail to produce normal amounts of testosterone, leading to low testosterone levels. The pituitary compensates by increasing LH and FSH, reflecting primary testicular failure. Therefore, the most informative lab result is the 47XXY karyotype.

Having a normal male karyotype would not account for the syndrome. Elevated testosterone is not expected—in fact, testosterone is typically low. Normal LH would be inconsistent, as LH is usually elevated due to reduced androgen production.