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Klinefelter syndrome usually is not diagnosed until the time of puberty. At this point, the boy's testicles fail to grow, and you may start to notice other symptoms.
To find out if your son has Klinefelter syndrome, your doctor will ask questions about his past health, do a physical exam, and order tests, such as a hormone test and chromosome analysis.
In adult men, other tests may be done, such as semen analysis.
Sometimes Klinefelter syndrome is found before a baby is born (prenatally). Genetic tests on cells collected from amniocentesis or chorionic villus sampling (CVS) can show when a baby boy has Klinefelter syndrome. So the condition may be found when a pregnant woman has genetic tests for another reason.