What does it measure?
The pituitary gland releases prolactin. Levels normally rise in pregnancy and breastfeeding. Outside those settings, the test may be requested for unexpected breast milk production, irregular or absent periods, or symptoms suggesting a pituitary or reproductive hormone problem. [1]
Before the test
- Sample
- A blood sample from a vein.
- Timing and preparation
- Collection is often planned a few hours after waking. Confirm fasting instructions and mention relevant medicines.
What can the result mean?
High prolactin has several possible explanations, including medicines, low thyroid function, kidney disease, and a prolactin-producing pituitary growth. Stress around the blood draw can also cause a rise. A low value is usually less informative unless a specific pituitary question is being investigated. [1]
When is it useful, and how is it read?
Prolactin is especially relevant with unexpected milk production, absent or irregular periods, or certain fertility and sexual symptoms. A persistent rise is assessed alongside pregnancy status when relevant, medicines, thyroid function, and possible macroprolactin before deciding whether pituitary imaging is needed. [2]
What can affect it?
Sleep, exercise, breast stimulation, pregnancy, and some psychiatric or nausea medicines affect interpretation. Mild elevations sometimes need a repeat under calmer conditions. If the result does not fit symptoms, the laboratory may check macroprolactin, a larger form with less biological activity. [1] [2]
Even the blood draw can briefly raise prolactin
Prolactin responds to stress, including anxiety around a needle. A mild unexpected rise can therefore lead to a carefully planned repeat, rather than an immediate conclusion about the pituitary gland. [1] [3]
Questions you might have
Does high prolactin always mean a pituitary tumor?
No. Pregnancy, medicines, low thyroid function, and other conditions can raise it. The result alone does not identify the cause. [1]
Why does waking time matter?
Prolactin changes through the day and with sleep. Recording when you woke up helps put the sample in context. [1]
What comes next?
Review medicines and thyroid results with your clinician before assuming a cause. Do not stop prescribed medicines independently. Persistent elevation may lead to further targeted testing; it does not mean everyone needs a scan. Mention new headaches or visual changes promptly. [1] [2]
Should we repeat this result or check medicines, thyroid function, and macroprolactin first?
The reference interval and units on your report are part of understanding your result. Understand units, reference intervals, and treatment targets.
Sources & references
Medical references & original research
Books we consulted
References that informed our explanations of the test and its context.
- Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. Elsevier; 2019.
Practical-section sources accessed: .
For general health education. Interpreting your result and deciding on tests or treatment requires your health context and a qualified clinician.
