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Causes of high prolactin levels
What are the physiologic causes of an elevated prolactin level that must be considered in the differential diagnosis of prolactin-secreting tumors? What levels can be reached under these circumstances?
The most important physiologic states in which prolactin is found to be elevated are pregnancy and lactation. During the third trimester of pregnancy, the prolactin level may reach 200 to 300 ng/mL. It then gradually decreases during postpartum week 1 despite continued lactation but may continue to rise acutely at the time of breastfeeding. Prolactin values are also elevated during sleep, strenuous exercise, stress, and nipple stimulation. In these cases, the elevation is mild, < 50 ng/mL.
Abnormal Causes of high prolactin levels Other than Prolactin Secreting Tumors and Underlying Mechanism of Abnormal Prolactin Production
| CAUSES | MECHANISM |
| Pituitary stalk interruption Trauma Surgery Pituitary, hypothalamic, or parasellar tumor Infiltrative disorders of the hypothalamus | Interference with the hypothalamic–pituitary pathways: Prolactin production increases because the tonic inhibition of prolactin secretion is interrupted; often accompanied by hypopituitarism |
| Pharmacologic agents: Phenothiazines Tricyclic antidepressants Alpha-methyldopa Metoclopramide Cimetidine Estrogens | Specific interference with dopaminergic input to the pituitary gland |
| Hypothyroidism | Increased thyrotropin-releasing hormone that stimulates prolactin release |
| Renal failure and liver cirrhosis | Decreased metabolic clearance of prolactin; also, increased production in chronic renal failure |
| Intercostal nerve stimulation Chest wall lesions Herpes zoster | Mimicking of the stimulation caused by suckling |
What are the typical levels of serum prolactin associated with these causes?
The prolactin level is usually mildly elevated, 30 to 50 ng/mL, and rarely above 100 ng/mL, when the cause of the elevated prolactin is not a prolactin-secreting tumor.
