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Prolactin

Prolactin ("PRL") is a blood test used to measure a protein that causes humans to produce milk. Levels that are significantly above the normal range can indicate medical problems in some cases.

Expected values

Although reference values vary between different labs, prolactin levels are usually expected to be less than about 25 ng/mL (532 mIU/L) (Thapa & Bhusal, 2023).

Prolactin levels are very often mildly elevated in people who take feminizing hormone therapy, often as a result of high estrogen levels or cyproterone acetate use. A range of other factors including common psychiatric medications and stress can also cause mild elevations. (Hembree at al., 2017; Sobrinho, 2003).

Prolactin levels below 47 ng/mL (1000 mIU/L) are rarely cause for serious concern. Prolactin levels over approximately 188 ng/mL (4000 mIU/L) can indicate a type of prolactin-producing tumor known as prolactinoma that may require medical attention. (Inder & Jang, 2022).

Other information

Some guidelines suggest routine monitoring of prolactin levels in those who take feminizing hormone therapy (Hembree at al., 2017), while other guidelines only recommend testing it if symptoms suggesting prolactinoma such as headaches, vision changes, and unexpected breast milk production are present (Deutsch, 2016).

See also

References

  • Deutsch, M. B. (Ed.). (2016). Guidelines for the Primary and Gender-Affirming Care of Transgender and Gender Nonbinary People, 2nd Edition. San Francisco: University of California, San Francisco/UCSF Transgender Care. [URL] [PDF]
  • Hembree, W. C., Cohen-Kettenis, P. T., Gooren, L., Hannema, S. E., Meyer, W. J., Murad, M. H., Rosenthal, S. M., Safer, J. D., Tangpricha, V., & T'Sjoen, G. G. (2017). Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology and Metabolism, 102(11), 3869–3903. [DOI:10.1210/jc.2017-01658]
  • Inder, W. J., & Jang, C. (2022). Treatment of Prolactinoma. Medicina (Kaunas, Lithuania), 58(8), 1095. [DOI:10.3390/medicina58081095]
  • Sobrinho L. G. (2003). Prolactin, psychological stress and environment in humans: adaptation and maladaptation. Pituitary, 6(1), 35–39. [DOI:10.1023/a:1026229810876]
  • Thapa, S., & Bhusal, K. (2023). Hyperprolactinemia. In StatPearls. StatPearls Publishing. [PubMed]
  • UCSF Health. (2022). Prolactin blood test. [URL]