Prolactin Deficiency Workup

Updated: Sep 20, 2018
  • Author: Charles T Benson, MD, PhD; Chief Editor: George T Griffing, MD  more...
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Laboratory Studies

The prolactin level following administration of thyrotropin may be the best screening test for Sheehan syndrome.

Usually, no workup is necessary, because supplemental prolactin is not yet available for treatment; however, suspicion of the disease can be confirmed by administering thyrotropin-releasing hormone or an antidopaminergic agent (eg, metoclopramide) and measuring prolactin levels. Failure to respond (rise in the level of prolactin) in the setting of the challenge is diagnostic.

The following tests can also be performed: prolactin assay in the third trimester or in peripartum women; LH, FSH, thyrotropin, and free thyroxine; and other tests as necessary to diagnose anterior hypopituitarism.

The author recommends that female patients who are interested in lactation and have suspected anterior pituitary dysfunction have prolactin measured in the third trimester of pregnancy or peripartum. This test can then be used to ascertain the possibility of puerperal alactogenesis. In this way, the patient can be forewarned of her inability to support lactation, and a recommendation for formula and bottle-feeding can be made. This enables the patient to avoid the often traumatic experience of waiting for her milk to come in, with this event instead being predicted by a simple laboratory test. Third trimester prolactin levels in normal pregnancies are often 150-250 mcg/L.

Normal baseline serum prolactin levels are less than 20 mcg/L in nongravid women and are usually less than 10 mcg/L in men. During pregnancy, serum levels may reach 200-500 mcg/L.

  • Prolactin is secreted in a pulsatile manner, with a distinct circadian pattern. [21, 22, 23] Circulating prolactin levels are lowest at midday (noon), with a modest increase occurring during the afternoon.

  • Prolactin levels increase shortly (60-90 min) after onset of sleep, peaking in the early morning.

  • Prolactin levels also rise in response to stress, food, serotonin, acetylcholine, opiates, estrogens, thyrotropin-releasing hormone, and angiotensin II.


Imaging Studies

Consider pituitary imaging if anterior pituitary dysfunction is suspected. Magnetic resonance imaging (MRI) is the usual imaging procedure.