Annals of Clinical Biochemistry > Volume 45, Number 3 > Pp. 256-259

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Original Articles

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

Sweta Ram¹, Beverley Harris², Joseph J R Fernando³, Rousseau Gama^1,4 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 used to detect hyperprolactinaemia caused by macroprolactin. We report two cases of hyperprolactinaemia in which a low recovery of serum prolactin (PRL) after PEG precipitation indicated the presence of macroprolactin, but no macroprolactin was detected by gel filtration chromatography (GFC). Both cases had elevated concentrations of serum globulin (IgG myeloma and polyclonal hypergammaglobulinaemia due to human immunodeficiency virus [HIV] infection), which prompted us to investigate further the effect of serum globulin on the specificity of the PEG precipitation procedure.

Methods: The effect of increasing concentrations of gamma globulin on the precipitation of PRL by PEG was studied by adding purified human gamma globulin to serum. Ten samples from HIV-infected patients, 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 PRL recoveries of <60% following PEG precipitation showed a substantial macroprolactin component on GFC.

Conclusions: Monomeric PRL is co-precipitated with serum globulins by PEG. Increased serum globulin concentrations can increase the amount of monomeric PRL precipitated by PEG giving a false estimate of the monomeric PRL and the erroneous impression that macroprolactin is present. The results of the PEG precipitation test should be interpreted with caution in patients with elevated serum globulin concentrations.

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This article has been cited by other articles:

				N F Jassam, A Paterson, C Lippiatt, and J H Barth Macroprolactin on the Advia Centaur: experience with 409 patients over a three-year period Ann Clin Biochem, November 1, 2009; 46(6): 501 - 504. [Abstract] [Full Text] [PDF]

				M. Fahie-Wilson and D. Halsall Polyethylene glycol precipitation: proceed with care Ann Clin Biochem, May 1, 2008; 45(3): 233 - 235. [Full Text] [PDF]