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Endocrine Abstracts (2006) 11 P713

ECE2006 Poster Presentations Reproduction (80 abstracts)

Hyperprolactinaemia due to big prolactin

JA Ahlquist 1 , AR Ellis 2 & MN Fahie-Wilson 1


1Southend Hospital, West Cliff on Sea, United Kingdom; 2UK NEQAS, Royal Infirmary, Edinburgh, United Kingdom.


Prolactin is present in serum in a variety of forms defined by different molecular masses. Macroprolactin is the best-known variant, a high molecular mass (150–170 kD) form of prolactin usually representing a prolactin–IgG complex which reacts in immunoassays causing apparent hyperprolactinaemia. Big-prolactin is a smaller high molecular mass (50–60 kDa) form of prolactin found more commonly than macroprolactin; however, the origin and significance of big-prolactin are poorly understood. Screening for larger molecular mass forms of prolactin is performed by measurement of serum prolactin after polyethylene glycol (PEG)-precipitation; low recovery (<40%) indicates the presence of macroprolactin, and intermediate recovery (40–60%) may require gel filtration chromatography (GFC) for clarification. We report the results of Sephacryl S-100 high resolution GFC to study the contribution of big-prolactin to total serum prolactin in 17 consecutive hyperprolactinaemic serum samples (total prolactin 724–7743 mU/l) with intermediate recovery after PEG-precipitation. Big-prolactin was the predominant high molecular mass prolactin form in 15 (79%) cases, representing 17–49% of total serum prolactin (56–91% of the high molecular mass forms). Chromatography of the precipitate after re-dissolution confirmed that PEG precipitates both macroprolactin and big-prolactin. Chromatography after adsorption of serum with protein G-Sepharose showed that only part of the big-prolactin peak was adsorbed, indicating an IgG component. Re-assay of big-prolactin chromatography fractions in seven commercial immunoassays confirmed that big-prolactin reacts in all prolactin assays widely used in the United Kingdom.

We conclude that, in cases of intermediate prolactin recovery after PEG-precipitation, big-prolactin is a substantial component of total serum prolactin and contributes to the hyperprolactinaemia seen in these cases. The molecular nature of big-prolactin remains unclear, but our data suggest that an IgG component is involved. Further work is required to define the biological activity of big-prolactin and thus to guide clinical interpretation of the results in these cases.

Volume 11

8th European Congress of Endocrinology incorporating the British Endocrine Societies

European Society of Endocrinology 
British Endocrine Societies 

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