Does polycystic ovary syndrome (PCOS) cause hyperprolactinemia?

PCOS is characterized by hyperandrogenism (excessive testosterone and other androgens), anovulatory cycles (menstrual cycles where an egg is not released), and ovarian cysts seen on ultrasound. The commonly used Rotterdam criteria require that two of these three criteria be present to diagnose PCOS.^[1]

Hyperprolactinemia might also result in symptoms of hyperandrogenism and could cause infertility and anovulation. Because of this similarity, doctors in the 1950s started investigating the possibility that PCOS might cause hyperprolactinemia. Studies done at the time showed overlapping symptoms, and blood tests supported the link, so it was quite a convincing hypothesis.

However, modern science and technology have improved our diagnostic abilities when it comes to hyperprolactinemia. In studies done prior to the 2000s, blood tests could not measure macroprolactin, and MRI scans could only pick up large prolactinomas (prolactin-producing tumors). Modern testing can see prolactinomas under even 3 mm in diameter. Macroprolactin can be tested for when the cause of hyperprolactinemia remains uncertain. These two tests explained the raised prolactin levels in many cases that had previously been attributed to PCOS.

Recent studies show that these two are likely separate entities, and people with PCOS who have high prolactin levels should undergo further testing to find a cause for the hyperprolactinemia. While more studies are needed to confirm these findings, current evidence suggests that PCOS is most likely not a cause of hyperprolactinemia.^[2][3]

It is also worth noting that new diagnostic tools also helped several people misdiagnosed with PCOS. In some cases, the symptoms attributed to PCOS were in fact caused by hyperprolactinemia, so hyperandrogenism and infertility could be successfully treated with cabergoline.^[2]