macroprolactin


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macroprolactin

A large (±100-kD), noncleaved, physiologically inactive form of prolactin, which is bound to IgG and interferes with immunoassays.
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Sera containing various amounts of macroprolactin were precipitated with PEG and also fractionated by gel filtration.
Two pitfalls have frequently been reported for prolactin assays: the "hook" effect may yield false-negative results when the prolactin concentration is very high (1); and the presence in serum of a high proportion of a biologically inactive but immunologically reactive form of prolactin (macroprolactin) may yield false-positive results (2).
The 23-kDa monomer is the predominant form in the general population, but other circulating species include the 50-kDa form (big PRL) and the 150--to 170-kDa macroprolactin (big big PRL) (1,2).
It is well recognized that circulating prolactin may exist in several forms, including little (monomeric), big, and big, big (macroprolactin) prolactin with molecular masses of 23, 50, and 150-170 kDa, respectively (1).
The most common form is macroprolactin, an antibody-antigen complex of prolactin (PRL) and immunoglobulin G with a molecular mass of 150-170 kDa (1-4).
(1) presented two clinical cases demonstrating the diagnostic confusion created by cases of hyperprolactinemia that are attributable to the presence of macroprolactin. The authors urged manufacturers of prolactin (PRL) reagents to (a) indicate in their product literature the extent to which macroprolactin interferes in their assays, and (b) have available a validated method to confirm the presence of macroprolactin.
Macroprolactin is a complex of prolactin with immunoglobulin (IgG) that in vivo appears to have limited or no biological activity, possibly because of the failure of the high-molecular weight complex to cross capillary walls (1).
(1) used the Wallac Delfia immunofluorometric assay to demonstrate that macroprolactin is a common cause of apparent hyperprolactinemia, and this confirms our experience (2) and that of others (3).
Serum macroprolactin concentrations were sought in the group with idiopathic hyperprolactinemia and the complaints of these patients and their responses to treatment (medication and/or surgery) were evaluated in detail.
In circulation, prolactin exists in different forms: a monomeric form whose molecular weight (MW) is 22 kDA, a polymeric form, "big prolactin" whose MW is 50-60 kDa, and a larger polymeric form, "macroprolactin," whose MW is greater than 100 kDa.
However, hyperprolactinemia in patients undergoing renal replacement therapy (RRT) does not consist abundantly of macroprolactin (>50 kDa) isoforms [1].
(4,5) Prolactin can be found in the circulation in one of three isoforms based on its molecular weight: monomeric PRL (small PRL; molecular weight 23 kDa), dimeric PRL (medium PRL; molecular weight 50-60 kDa), and polymeric PRL [large PRL/ macroprolactin (maPRL); molecular weight 150-170 kDa).