Which lab tests are performed to assess hyperprolactinemia in hyperpituitarism?

Updated: Oct 24, 2016
  • Author: Alicia Diaz-Thomas, MD, MPH; Chief Editor: Robert P Hoffman, MD  more...
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See the list below:

  • Serum PRL: A single PRL measurement may be sufficient to diagnose a prolactinoma if the value is greater that 200 ng/mL. Because PRL is secreted in a pulsatile fashion, a mildly increased concentration may be difficult to interpret. In this situation, casual morning samples obtained on 3 separate days should be examined before a prolactinoma is diagnosed. The serum PRL level is roughly proportional to the mass of the tumor. Small tumors can cause elevations of serum PRL lower than those values commonly observed with hyperprolactinemia from other causes.

  • Thyrotropin-releasing hormone (TRH) stimulation test: In healthy patients, intravenous TRH results in a brisk rise in serum PRL in 15-30 minutes, with peak values at least twice the baseline value. In contrast, patients with PRL-secreting tumors usually show little or no PRL increment in response to TRH, rarely exceeding a 100% rise. Patients with elevated serum PRL from other causes usually show a more normal response, with a rise in PRL of at least 100% following administration of TRH.

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