Macroprolactinemia refers to a patient with a large circulating form of prolactin. Because reagent antibodies to prolactin bind heavily to this form the patient may be thought to hyperprolactinemia and undergo an extensive and unnecessary workup.

Form of Prolactin

Molecular Weight

normal monomer

22,000 Daltons

"big" form

50,000 to 60,000 Da

"big-big" (macro), a complex of prolactin and IgG

about 150,000 Daltons


Macroprolactin may be removed by:

(1) PEG (polyethylene glycol) precipitation

(2) gel filtration chromatography


Clinical features of macroprolactinemia:

(1) presence of a high value on the serum prolactin assay

(2) greatly reduced serum prolactin value after macroprolactin is removed. If the amount of prolactin is within the normal range then the patient had pseudohypoprolactinemia.


Any sample with a high serum prolactin (> 700 mIU/L) should be screened for macroprolactin.


The presence of macroprolactinemia does not exclude the possibility of true hyperprolactinemia.


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