What is the Difference Between Prolactin and Macroprolactin?

Prolactin and macroprolactin are two forms of the hormone prolactin, which is secreted mainly by the pituitary gland and is best known for its role in enabling females to produce milk. The key differences between prolactin and macroprolactin are:

1. Biological Activity: Prolactin is a physiologically active protein, while macroprolactin is a physiologically inactive protein isoform of prolactin.
2. Molecular Weight: Prolactin has a molecular weight of 23 kDa, while macroprolactin has a molecular weight greater than 100 kDa.
3. Composition: Prolactin is a monomeric protein, whereas macroprolactin is a large antigen-antibody complex, typically consisting of prolactin and immunoglobulin G (IgG).

In most cases, hyperprolactinemia is a result of high levels of monomeric prolactin, which may be due to excess production as with a prolactinoma or due to disinhibition by compression. Macroprolactin is detected by all laboratory tests that measure prolactin in blood, which can lead to misdiagnosis of hyperprolactinemia in many people, especially those with symptoms such as infertility or menstrual problems.

Comparative Table: Prolactin vs Macroprolactin

Here is a table comparing the differences between prolactin and macroprolactin:

Prolactin and macroprolactin are both proteins found in females and males, and they are present in adult serum. However, prolactin is a bioactive protein that plays a crucial role in milk production, while macroprolactin is a non-bioactive isoform of prolactin with limited bioavailability.