Prevalence and predictors of hyperprolactinemia in subclinical hypothyroidism

Hyperprolactinemia has been reported in 0-57% of primary hypothyroidism. Data on hyperprolactinemia in subclinical hypothyroidism (ScH) is scant and inconsistent. This study aimed to determine the prevalence and predictors of hyperprolactinemia in ScH.

Consecutive patients diagnosed to have normal thyroid function, ScH or overt primary hypothyroidism underwent serum prolactin, gonadotropins, testosterone and estradiol estimation. Patients with pregnancy, pituitary adenomas, secondary hypothyroidism, hyperthyroidism, comorbid states and drug-induced hyperprolactinemia were excluded.

From initially screened 4950 patients, hormonal data from 2848 individuals who fulfilled all criteria were analyzed. The occurrence of hyperprolactinemia (females:males) was highest in primary hypothyroidism (42.95%:39.53%) (n=192), followed by ScH (35.65%:31.61%) (n=770) and euthyroid individuals (2.32%:2.02%) (n=1886) (P<0.001). Hyperprolactinemia in ScH with TSH 5-7.5, 7.5-10 and >10mIU/L (females: males) was 25.56%:20.73%, 49.07%:50% and 61.43%:35.71% respectively (P<0.001). Significant positive correlation between TSH and prolactin was noted in ScH and primary hypothyroidism. In females, testosterone was lowest in patients with primary hypothyroidism. In males, serum estradiol was significantly higher, and testosterone significantly lower in men with ScH and primary hypothyroidism. Regression analysis revealed serum TSH followed by free T₄, to be best predictors of serum prolactin in both sexes.

Hyperprolactinemia is common in ScH, especially in those with TSH>7.5mIU/L. ROC analysis confirmed that TSH≥7.51mIU/L in females and ≥8.33mIU/L in males had a sensitivity of ≈50% with a very high specificity of >90% in detecting hyperprolactinemia. Prolactin screening may be warranted in ScH with TSH>7.5mIU/L, and may form an indication for treating ScH.