Serum Total Prolactin and Monomeric Prolactin Reference Intervals Determined by Precipitation with Polyethylene Glycol: Evaluation and Validation on Common ImmunoAssay Platforms

Abstract

Background: Macroprolactin is an important source of immunoassay interference that commonly leads to misdiagnosis and mismanagement of hyperprolactinemic patients. We used the predominant immunoassay platforms for prolactin to assay serum samples treated with polyethylene glycol (PEG) and establish and validate reference intervals for total and monomeric prolactin. Methods: We used the Architect (Abbott), ADVIA Centaur and Immulite (Siemens Diagnostics), Access (Beckman Coulter), Elecsys (Roche Diagnostics), and AIA (Tosoh) analyzers with samples from healthy males (n = 53) and females (n = 93) to derive parametric reference intervals for total and post-PEG monomeric prolactin. Concentrations of immunoreactive prolactin isoforms in serum samples from healthy individuals were established by gel filtration chromatography (GFC). We then used samples from 22 individuals whose hyperprolactinemia was entirely attributable to macroprolactin and 32 patients with true hyperprolactinemia to compare patient classifications and prolactin concentrations measured by GFC with the newly derived post-PEG reference intervals. Results: Parametric reference intervals for post-PEG prolactin in male and female serum samples, respectively, were (in mIU/L): 61–196, 66–278 (Centaur); 63–245, 75–381 (Elecsys); 70–301, 92–469 (Access); 72–229, 79–347 (Architect); 73–247, 83–383 (AIA); and 78–263, 85–394 (Immulite). Concordance between GFC and immunoassay-specific post-PEG reference intervals was observed in 311 of 324 cases and for 31 of 32 patients with true hyperprolactinemia and 17 of 22 patients with macroprolactinemia. Results leading to misclassification occurred in a few analyzers for 5 macroprolactinemia patient samples with relatively minor increases in post-PEG prolactin (mean 61 mIU/L). Conclusions: Our validated normative reference data for sera pretreated with PEG and analyzed on the most commonly used immunoassay platforms should facilitate the more widespread introduction of macroprolactin screening by clinical laboratories.

Macroprolactinaemia: a biological diagnostic strategy from the study of 222 patients

“…The monomeric PRL concentration after GFC (GFC monomeric PRL) was calculated according to the formula: (amount of monomeric PRL from GFC (%)/100)!PRL concentration in the native serum obtained by RIA (mg/l). We considered that normal monomeric PRL values obtained from GFC for women were %21 mg/l (%444 mUI/l), as reported by Beltran et al (1).…”

“…Monomeric PRL is generally the most common form circulating in healthy subjects and in hyperprolactinaemic sera (1,2). Macroprolactinaemia (MPRL) is the condition which results when the high molecular mass forms (bPRL, bbPRL) are predominant.…”

“…We evaluated two MPRL screening methods: first, the rate of PRL recovery in the supernatant after PEG precipitation and secondly, the ratio of PRL concentrations derived from two different assays (RIA and electrochemiluminescence assay with Prolactin II on a Roche cobas e 601 analyser). Furthermore, to assess alternative approaches for monomeric PRL quantification, PRL measurement with a low-reacting assay (Prolactin II assay on a Roche cobas e 601 analyser) and PRL measurement in the supernatant after PEG precipitation (1,22,25,26) were performed.…”

Importance of macroprolactinemia in hyperprolactinemia

“…However, PEG also induces a partial precipitation of monomeric PRL (up to 25%) so reliance on the relative percentage of recovery lacks specificity which may lead to an underestimated evaluation and misinterpretation of actual PRL levels [24]. This is especially important in cases when an excessive macroprolactin occurs in patient's serum simultaneously with supraphysiological concentrations of monomeric PRL [9,26,29]. Furthermore, it has been reported that the presence of PEG in the sample can interfere with some PRL immunoassay procedures [30].…”

“…Furthermore, it has been reported that the presence of PEG in the sample can interfere with some PRL immunoassay procedures [30]. To avoid such problems, it has been recommended that each laboratory, undertaking macroprolactin screening, must establish method-specific reference intervals derived by use of PEG-treated sera from healthy individuals [9,26,29]. In routine laboratory diagnostics the post-PEG modified reference range is the best means to accurately identify patients with true hyperprolactinemia [9].…”