Which diagnostic test is most likely to confirm the diagnosis for a 13-year-old female with primary amenorrhea and short stature?

The most likely diagnostic test to confirm the diagnosis for a 13-year-old female presenting with primary amenorrhea and short stature is karyotyping. This test is crucial in this scenario because the combination of primary amenorrhea and short stature raises suspicion for conditions such as Turner syndrome, which is characterized by the presence of a missing or incomplete X chromosome. Karyotyping allows for the analysis of the individual’s chromosomes, enabling clinicians to identify any chromosomal abnormalities, such as the characteristic 45,X pattern seen in Turner syndrome.

In the case of pelvic ultrasound, although it can provide valuable information about the anatomy of the reproductive system, it is not definitive for identifying chromosomal issues or conditions like Turner syndrome. Serum hCG levels are primarily used to assess pregnancies and would not be relevant in a situation where primary amenorrhea and short stature are the key concerns. Thyroid function tests could evaluate for hypothyroidism, which may affect menstrual cycles, but they would not specifically confirm a diagnosis related to chromosomal abnormalities responsible for primary amenorrhea. Thus, karyotyping is the most appropriate test in this context.