Klinefelter syndrome can be identified before birth (prenatally) through amniocentesis or chorionic villus sampling (CVS). It also can be diagnosed in childhood, during puberty, or in adulthood by a medical history, physical exam, and a chromosome test called a karyotype. Other lab tests, such as hormone tests or a semen analysis, may be done if Klinefelter syndrome is suspected.

Prenatal testing

Amniocentesis and chorionic villus sampling (CVS) are not routine prenatal tests. They usually are done when there is a family history of genetic disorders (such as Klinefelter syndrome) or when the mother is older than 35.

Testing in childhood or during puberty

Klinefelter syndrome usually is not diagnosed before the preteen years because there are no symptoms or because symptoms go unnoticed until puberty. However, a doctor may suspect Klinefelter syndrome when a young boy has difficulty learning to talk, read, or write.

During puberty, some males may be suspected of having Klinefelter syndrome, including those who:

• Are taller than other males in their family and have long legs.
• Have small testicles that do not increase in size as puberty progresses.
• Have enlarged breast tissue that persists for more than 2 years.
• Have learning or social problems (such as lacking self-confidence and being shy, immature, or dependent).
• Have mild mental retardation. Klinefelter syndrome is present in about 1% of males with mental retardation.³

Tests for Klinefelter syndrome during childhood or puberty usually include a medical history, physical exam, and karyotype.

Adult testing

Klinefelter syndrome may not be diagnosed until adulthood when a man seeks medical care to determine the cause of his infertility. About 3% of infertile men have Klinefelter syndrome.³ Tests include a medical history, physical exam, and karyotype. A man may also have hormone tests and a semen analysis.