Diagnosis of Klinefelter Syndrome Prenatal diagnosis often when cytogenetic testing is done for other reasons such as advanced maternal age Detected postnatally on clinical appearance Cytogenetic testing by karyotyping, fluorescent in situ hybridization (FISH) analysis, and / or chromosomal microarray analysis The diagnosis of Klinefelter syndrome is suspected on physical examination of an adolescent with small testes and gynecomastia.