Serum prolactin levels in untreated primary hypothyroldism

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The serum prolactin level was found to be elevated (>14.0 ng/ml) in 39 per cent of patients with untreated primary hypothyroidism, none of whom were receiving drugs known to affect serum prolactin levels. The mean serum thyroid-stimulating hormone (TSH) (± SEM), thyroxine (T 4) and triiodothyronine (T 3) levels prior to therapy were, respectively, 106.0 μU/ml ± 19.3, 0.9 μg/dl ± 0.2, 50.6 ng/dl ± 5.8. The mean serum prolactin level in the hypothyroid group (14.3 ng/ml ± 1.1; range: 4.7 to 42.0 ng/ml; 49 subjects) was significantly higher (P < 0.01) than in the euthyroid controls (8.2 ng/ml ± 0.5; range 5.1 to 14.0 ng/ml; 24 subjects). The mean serum prolactin level in the hypothyroid women (15.4 ng/ml ± 1.3; range 4.7 to 42.0 ng/ml; 39 subjects) was significantly higher (P < 0.002) than in the euthyroid female controls (8.1 ng/ml ± 0.7; range 5.1 to 14.0 ng/ml; 15 subjects). The mean serum prolactin level in the hypothyroid men (10.3 ng/ml ± 1.4; range 5.1 to 18 ng/ml; 10 subjects) was not significantly different from that in the male controls (8.3 ng/ml ± 0.7; range 5.3 to 13 ng/ml; nine subjects). A significant correlation was found between log serum prolactin and log serum TSH (r = 0.34, P < 0.05), suggesting that the elevated serum prolactin level in primary hypothyroidism may be mediated by a common factor, such as TRH. Despite the increased frequency of elevated serum prolactin levels, galactorrhea is an uncommon accompaniment of primary hypothyroidism.