Low thyroid levels associated with subclinical hypothyroidism, in combination with raised prolactin levels, have been implicated in ovulatory dysfunction that leads to infertility. Few studies have examined the prevalence of hyperprolactinemia in subclinical hypothyroidism. A cross-sectional study of the relationship between these two disease states was recently published in the Journal of Family Medicine and Primary Care.

This cross-sectional study included 150 patients in India with subclinical hypothyroidism. Thyroid-hormone levels, along with serum prolactin levels, were measured utilizing an electrochemiluminescence assay.  The mean age of patients was 31.82 ± 6.18 years, with 90% being females and 10% being males. Of the 150 patients, 18% had hyperprolactinemia, a value that is consistent with the reported literature. Overall, the most common complaints reported by participants included menstrual irregularities (16.7%) and infertility (16.7%). Researchers believe that this finding explains the causative role of hyperprolactinemia in infertility.

Study results also revealed a positive correlation between low thyroid-stimulating hormone (TSH) levels and elevated serum prolactin levels (P = .007). Additionally, patients with higher TSH values (7.5-10 mIU/L) had a significantly higher prevalence of hyperprolactinemia (33%) compared to patients with TSH levels between 5 and 7.4 mIU/L, who had a prevalence of 13.7%. These results led to the conclusion that more severe hypothyroidism, as displayed by higher TSH levels, leads to a greater thyrotropin-releasing hormone–mediated prolactin release.

Investigators concluded that raised prolactin levels were found in 18% of patients with subclinical hypothyroidism. Additionally, there was a positive correlation between serum TSH and prolactin levels. Along with this finding, it was revealed that the prevalence of infertility was higher in the presence of hyperprolactinemia than in the presence of normoprolactinemia in patients with subclinical hypothyroidism. Although further studies are needed to examine the association between hyperprolactinemia and subclinical hypothyroidism, routine evaluation of prolactin serum level may be recommended in patients with subclinical hypothyroidism.

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