Many boys with Klinefelter syndrome show few or only mild signs. Thus, the condition may go undiagnosed until adulthood or it may never be diagnosed. For others, the condition has a noticeable effect on growth or appearance. A small percentage of males with Klinefelter syndrome are diagnosed before birth. The syndrome might be identified in pregnancy during a procedure to examine fetal cells drawn from the amniotic fluid (amniocentesis) or placenta for another reason — such as being older than age 35 or having a family history of genetic conditions. Klinefelter syndrome may be suspected during a noninvasive prenatal screening blood test. To confirm the diagnosis, further invasive prenatal testing such as amniocentesis is required.
To diagnose the syndrome a doctor will likely do a thorough physical exam and ask detailed questions about symptoms and health. This may include examining the genital area and chest, performing tests to check reflexes, and assessing development and functioning. The main tests used to diagnose Klinefelter syndrome are:
- Hormone testing. Blood or urine samples can reveal abnormal hormone levels that are a sign of Klinefelter syndrome.
- Chromosome analysis. Also called karyotype analysis, this test is used to confirm a diagnosis of Klinefelter syndrome. A blood sample is sent to the lab to check the shape and number of chromosomes.