Autoimmune thyroid disease - is high prolactin a risk factor?

Background In addition to its classic effect of lactation, prolactin (PRL) has begun to attract attention for its non-classic effects, particularly on the immune system. Objective This study aimed to compare the prevalence of autoimmune thyroid disease (AITD), thyroid autoantibodies and thyroid function tests (TFTs) in patients with hyperprolactinemia (HPRL) of at least 25 ng/ml and in healthy controls with PRL of less than 25 ng/ml.We conducted a retrospective case-control study at a single tertiary referral centre. All study participants underwent measurement of antibodies to thyroglobulin (anti-Tg), thyroid peroxidase (anti-TPO), TSH and fT4 levels, as well as ultrasonographic thyroid pattern assessment. Results The AITD rate was found to be 33.5% in those with PRL ≥ 25. In the healthy control group, this rate was 23.5%, and this difference was statistically significant (p = 0.006). Among those with PRL ≥ 25, Anti-TPO and Anti-Tg levels, as well as TSH levels, were significantly higher and sT4 levels were significantly lower compared to the control group (p < 0.001).. There was a positive relationship between PRL levels and TSH, Anti-Tg, and Anti-TPO levels, while there was a negative relationship with sT4 levels, all of which were statistically significant but relatively weak .The ROC analysis revealed that the PRL level was 21.77 ng/mL for detecting Anti-TPO positivity and Anti-Tg positivity, the cut-off value was determined to be 21.92 ng/mL Conclusions There is an increase in the frequency of AITD and thyroid autoantibodies in HPRL patients. We can conclude that exceeding the PRL threshold value increases the risk.