What is macroprolactin? When should one check for it?

Normally 85% of circulating prolactin is monomeric (23.5 kDa). The remaining 15% is made of a covalently bound dimer, “big prolactin,” and a much larger polymeric form, “big big prolactin.” The term macroprolactinemia denotes the situation in which a preponderance of the circulating prolactin consists of these larger molecules. Macroprolactin are less bioactive, and macroprolactinemia should be suspected when typical symptoms of hyperprolactinemia are absent. Macroprolactin should be tested in patients with hyperprolactinemia who are asymptomatic.