B

A markedly elevated FSH/LH profile indicates primary ovarian insufficiency (hyper-gonadotropic hypogonadism). The diagnosis requires confirmation that ovarian estrogen production is low, so the next logical test is to measure serum estradiol; low estradiol together with high FSH/LH establishes the diagnosis and guides further evaluation (e.g., karyotype, POI work-up) [Christin-Maitre, 2021, PMID 34508691].