What are the normal levels of serum prolactin? Are they different in men and women? What levels are seen in patients with prolactin-secreting tumors?
The normal serum prolactin level is < 15 or 30 ng/mL, depending on the laboratory. Women tend to have slightly higher levels than men, probably because of estrogen stimulation of prolactin secretion. In patients with prolactin-secreting tumors, the levels are usually > 100 ng/mL but may be as low as 30 to 50 ng/mL if the tumor is small. A level > 200 ng/mL is almost always indicative of a prolactin-secreting tumor. Very high prolactin levels may be found to be falsely normal because of the high-dose hook effect of the assay; if clinically indicated, the sample should be assayed again after dilution.