A collegiate athlete is evaluated by a physician because she has never experienced a menstrual period. The patient reports no medical issues and takes no medications. On physical examination, she has Tanner stage V breast development but notably sparse axillary and pubic hair. Pelvic examination reveals a shortened, blind-ending vaginal pouch. A subsequent transabdominal ultrasound confirms the absence of a uterus, cervix, and fallopian tubes. While cytogenetic testing is pending, which of the following is the most appropriate next step in laboratory evaluation?
- Serum testosterone levelAnswer
- BSerum follicle-stimulating hormone level
- CSerum prolactin level
- DSerum estradiol level
- ESerum 17-hydroxyprogesterone level
Answer
The most appropriate next step in laboratory evaluation is to measure the serum testosterone level.
The correct answer is the serum testosterone level. When evaluating primary amenorrhea, the initial branching point is whether the uterus is present or absent. In this patient, the uterus is absent, which narrows the differential diagnosis down to Müllerian agenesis (Mayer-Rokitansky-Küster-Hauser syndrome) or complete androgen insensitivity syndrome (AIS). The definitive test is a karyotype, but this can take several weeks to return. In the interim, measuring a serum testosterone level is the most appropriate initial laboratory step. In complete AIS (46,XY), testosterone is produced by cryptorchid testes and levels will be in the normal-to-high male range. In Müllerian agenesis (46,XX), ovarian function is normal, and testosterone levels will be in the normal female range. The patient's sparse axillary and pubic hair strongly suggests complete AIS, as the androgen receptors are unresponsive.
Step-by-Step Solution
Key Concept
In patients presenting with primary amenorrhea and an absent uterus, the most appropriate initial laboratory evaluation includes a karyotype and a serum testosterone level to differentiate between Müllerian agenesis and complete androgen insensitivity syndrome.