Prolactin is a pituitary hormone whose classical role is milk production after childbirth. Outside that setting it acts largely as a marker of pituitary function, because sustained excess suppresses the hormonal signals that drive the ovaries and testes. The test therefore usually appears when cycles, fertility or libido are being investigated.
No readings for this marker yet.
Raised prolactin most often reflects a benign pituitary adenoma, an underactive thyroid, pregnancy or breastfeeding, chest wall stimulation, or medication, particularly antipsychotics and some antiemetics and antidepressants. Modest elevations frequently come from stress around the blood draw alone and disappear on a calm repeat sample. Low prolactin rarely carries clinical weight on its own. A raised result is a prompt to repeat the test and consult a doctor, not a finding in itself.
Levels rise with sleep, stress, exercise, nipple stimulation and even the venepuncture, so the sample is usually taken in the morning, at rest, some hours after waking; macroprolactin, an inert bound form, can inflate the figure and the laboratory can screen for it. Prolactin is read alongside LH, FSH, testosterone or estradiol, since its main effect is to suppress that axis, and thyroid testing is commonly added.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.