What laboratory test is considered a first-line evaluation for suspected polycystic ovary syndrome (PCOS)?

The first-line evaluation for suspected polycystic ovary syndrome (PCOS) involves assessing serum total testosterone levels. In women with PCOS, elevated androgen levels, including testosterone, are common and contribute to symptoms such as hirsutism, acne, and irregular menstrual cycles. This test helps to identify hyperandrogenism, which is one of the key diagnostic criteria for PCOS.

Other tests like serum thyroxine, FSH (follicle-stimulating hormone), and serum prolactin are not specific for diagnosing PCOS. Serum thyroxine is primarily used to evaluate thyroid function, while FSH is involved in reproductive hormone regulation but does not directly assess androgen levels. Serum prolactin is checked in the context of assessing disorders related to lactation or pituitary function rather than for diagnosing PCOS. Therefore, testing for serum total testosterone is the most relevant initial step in the workup of a patient suspected of having PCOS due to its direct correlation with hyperandrogenism.