False-positive polyethylene glycol precipitation tests for macroprolactin due to increased serum globulins

Ann Clin Biochem 2008;45:256-259
© 2008 Association for Clinical Biochemistry


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Original Articles

Sweta Ram1,
Beverley Harris2,
Joseph J R Fernando3,
Rousseau Gama1,4 and
Michael Fahie-Wilson5

1 Department of Clinical Chemistry, New Cross Hospital, Wolverhampton, West Midlands WV10 0QP, UK;
2 Clinical Biochemistry, Royal United Hospital, Bath BA1 3NG, UK;
3 Department of Genito-Urinary Medicine, New Cross Hospital, Wolverhampton WV10 0QP, UK;
4 Research Institute, School of Biological Sciences, Wolverhampton University, West Midlands WV1 1SB, UK;
5 Clinical Biochemistry, Southend Hospital, Westcliff-on-Sea, Essex SS0 0RY, UK

Corresponding author: Mr M Fahie-Wilson. Email: mfahie-wilson{at}southend.nhs.uk

Background: The polyethylene glycol (PEG) precipitation test is widely usedto detect hyperprolactinaemia caused by macroprolactin. We reporttwo cases of hyperprolactinaemia in which a low recovery ofserum prolactin (PRL) after PEG precipitation indicated thepresence of macroprolactin, but no macroprolactin was detectedby gel filtration chromatography (GFC). Both cases had elevatedconcentrations of serum globulin (IgG myeloma and polyclonalhypergammaglobulinaemia due to human immunodeficiency virus[HIV] infection), which prompted us to investigate further theeffect of serum globulin on the specificity of the PEG precipitationprocedure.

Methods: The effect of increasing concentrations of gamma globulin onthe precipitation of PRL by PEG was studied by adding purifiedhuman gamma globulin to serum. Ten samples from HIV-infectedpatients, which showed a low recovery of PRL after PEG precipitation(<60%) were studied with GFC.

Results: Addition of gamma globulin decreased the recovery of PRL following precipitation with PEG and gamma globulin concentrations correlated inversely with PRL concentrations (r = 0.9429, P < 0.0167) and percentage recovery of PRL (r = –1.000, P < 0.005).Only one out of 10 samples from HIV-infected patients with PRLrecoveries of <60% following PEG precipitation showed a substantialmacroprolactin component on GFC.

Conclusions: Monomeric PRL is co-precipitated with serum globulins by PEG.Increased serum globulin concentrations can increase the amountof monomeric PRL precipitated by PEG giving a false estimateof the monomeric PRL and the erroneous impression that macroprolactinis present. The results of the PEG precipitation test shouldbe interpreted with caution in patients with elevated serumglobulin concentrations.

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M. Fahie-Wilson and D. Halsall
Polyethylene glycol precipitation: proceed with care
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