Understanding Raised Prolactin Levels with No Symptoms: The Role of Macroprolactin
Learn about macroprolactin, a cause of high prolactin levels without symptoms, and how it affects diagnosis and treatment.
Raised prolactin levels, known as hyperprolactinaemia, can sometimes occur without any noticeable symptoms. This can be due to a form of prolactin called macroprolactin. Understanding macroprolactin is important because it can prevent unnecessary tests and treatments.
What is Macroprolactin?
Macroprolactin is a complex of prolactin, a hormone, with immunoglobulin G (IgG), which are antibodies in the immune system. This complex has a large molecular mass, over 150 kilodaltons (kDa). Unlike regular prolactin, macroprolactin has low bioactivity because the antibodies can block prolactin from binding to its receptor sites. This means that even if the total prolactin level is high, the free, active prolactin is normal, leading to no symptoms.
Why Does Macroprolactin Matter?
The presence of macroprolactin is significant because it explains why some people with high prolactin levels do not experience symptoms typically associated with hyperprolactinaemia, such as menstrual irregularities or galactorrhea (unexpected milk production). The prevalence of macroprolactinaemia is about 10 to 25% in patients with high prolactin levels and around 3.7% in the general population. Recognizing macroprolactin can prevent unnecessary imaging tests and treatments.
Diagnosing Macroprolactinaemia
Laboratories diagnose macroprolactinaemia using a simple and cost-effective method called polyethylene glycol (PEG) precipitation. This test measures the percentage of prolactin that is macroprolactin. A PEG-precipitation ratio above 60%, or a recovery below 40%, indicates macroprolactinaemia. For confirmation, a more accurate but complex method called gel filtration chromatography can be used, although it is more time-consuming and expensive.
Impact on Treatment
If macroprolactinaemia is identified, it can prevent unnecessary treatments, such as medications or imaging studies that are not needed. The main harm of missing macroprolactin is undergoing unnecessary medical procedures, not leaving a condition untreated. Therefore, it is recommended that all patients with high prolactin levels be screened for macroprolactinaemia.
Frequently asked questions
What is prolactin? Prolactin is a hormone produced by the pituitary gland that plays a role in lactation and other functions in the body.
What are common symptoms of high prolactin levels? Symptoms can include irregular menstrual cycles, infertility, and unexpected milk production, but these are absent in cases of macroprolactinaemia.
How is macroprolactin different from regular prolactin? Macroprolactin is a larger molecule due to its combination with antibodies, which reduces its activity and prevents symptoms despite high total prolactin levels.
Why is it important to test for macroprolactin? Testing for macroprolactin helps avoid unnecessary treatments and procedures by distinguishing it from other causes of high prolactin levels that require intervention.
Can macroprolactinaemia be treated? Macroprolactinaemia itself typically does not require treatment because it does not cause symptoms or health issues.
When to see a doctor
If you have been told you have high prolactin levels, discuss with your doctor whether testing for macroprolactin is appropriate. This can help ensure that any further tests or treatments are truly necessary and appropriate.
Disclaimer: This information is not a substitute for professional medical advice. Always consult with a healthcare provider for decisions about your health.