Ram Sweta, Harris Beverley, Fernando Joseph J R, Gama Rousseau, Fahie-Wilson Michael
Department of Clinical Chemistry, New Cross Hospital, Wolverhampton, West Midlands, UK.
Ann Clin Biochem. 2008 May;45(Pt 3):256-9. doi: 10.1258/acb.2008.007233.
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.
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.
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.
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.
聚乙二醇（PEG）沉淀试验广泛用于检测由大分子催乳素引起的高催乳素血症。我们报告了两例高催乳素血症病例，其中PEG沉淀后血清催乳素（PRL）回收率低表明存在大分子催乳素，但凝胶过滤色谱法（GFC）未检测到大分子催乳素。两例患者血清球蛋白浓度均升高（一例为IgG骨髓瘤，另一例因人类免疫缺陷病毒[HIV]感染导致多克隆高球蛋白血症），这促使我们进一步研究血清球蛋白对PEG沉淀法特异性的影响。
通过向血清中添加纯化的人γ球蛋白，研究γ球蛋白浓度增加对PEG沉淀PRL的影响。对10例HIV感染患者的样本进行了研究，这些样本在PEG沉淀后PRL回收率较低（<60%），采用GFC进行检测。
添加γ球蛋白会降低PEG沉淀后PRL的回收率，γ球蛋白浓度与PRL浓度呈负相关（r = 0.9429，P < 0.0167），与PRL回收率百分比呈负相关（r = -1.000，P < 0.005）。在PEG沉淀后PRL回收率<60%的10例HIV感染患者样本中，只有1例在GFC上显示出大量的大分子催乳素成分。
单体PRL可被PEG与血清球蛋白共沉淀。血清球蛋白浓度升高会增加PEG沉淀的单体PRL量，从而对单体PRL产生错误估计，并错误地认为存在大分子催乳素。对于血清球蛋白浓度升高的患者，PEG沉淀试验结果的解释应谨慎。
