How do health care providers diagnose Klinefelter syndrome (KS)?

The only way to confirm the presence of an extra chromosome is by a karyotype test. A health care provider will take a small blood or skin sample and send it to a laboratory, where a technician inspects the cells under a microscope to find the extra chromosome. A karyotype test shows the same results at any time in a person’s life.

Tests for chromosome disorders, including KS, may be done before birth. To obtain tissue or liquid for this test, a pregnant woman undergoes chorionic villus sampling or amniocentesis.¹ These types of prenatal testing carry a small risk for miscarriage and are not routinely conducted unless the woman has a family history of chromosomal disorders, has other medical problems, or is above 35 years of age.

Factors that Influence When KS Is Diagnosed

Because symptoms can be mild, some males with KS are never diagnosed.²

Several factors affect whether and when a diagnosis occurs:

• Few newborns and boys are tested for or diagnosed with KS.
  • Although newborns in the United States are screened for some conditions, they are not screened for XXY or other sex chromosome differences.
  • In childhood, symptoms can be subtle and overlooked easily. Only about 1 in 10 males with KS are diagnosed before puberty.¹
  • Sometimes, visiting a health care provider will not produce a diagnosis. Some symptoms, such as delayed early speech, might be treated successfully without further testing for KS.
• Most XXY diagnoses occur at puberty or in adulthood.
  • Puberty brings a surge in diagnoses as some males (or their parents) become concerned about slow testes growth or breast development and consult a health care provider.
  • Many men are diagnosed for the first time in fertility clinics.³ Among men seeking help for infertility, about 15% have KS.⁴