Prevalence of macroprolactin detected by Elecsys 2010

Global Prevalence of Macroprolactinemia among Patients with Hyperprolactinemia: A Systematic Review and Meta-Analysis

Hyperprolactinemia (hPRL) often poses a diagnostic dilemma due to the presence of macroprolactin. Understanding the prevalence of macroprolactinemia (mPRL) has an important implication in managing patients with hPRL. The primary aim of this study was to determine the prevalence of mPRL globally and to explore selected factors influencing the prevalence estimate. Studies with original data related to the prevalence of mPRL among patients with hPRL from inception to March 2020 were identified, and a random effects meta-analysis was performed. Of the 3770 records identified, 67 eligible studies from 27 countries were included. The overall global prevalence estimate was 18.9% (95% CI: 15.8%, 22.1%) with a substantial statistical heterogeneity (I² = 95.7%). The highest random effects pooled prevalence was observed in the African region (30.3%), followed by Region of the Americas (29.1%), European (17.5%), Eastern Mediterranean (13.9%), South-East Asian (12.7%), and Western Pacific Region (12.6%). Lower prevalence was observed in studies involving both sexes as compared to studies involving only female participants (17.1% vs. 25.4%) and in more recent studies (16.4%, 20.4%, and 26.5% in studies conducted after 2009, between 2000 and 2009, and before 2000, respectively). The prevalence estimate does not vary according to the age group of study participants, sample size, and types of polyethylene glycol (PEG) used for detection of macroprolactin (PEG 6000 or PEG 8000). With macroprolactin causing nearly one-fifth of hPRL cases, screening for mPRL should be made a routine before an investigation of other causes of hPRL.

Hyperprolactinaemia: A guide for psychiatrists

Medications prescribed by psychiatrists are known to elevate serum prolactin levels, but hyperprolactinaemia remains underrecognised, as the adverse effects of an elevated prolactin are mostly not visible. Hyperprolactinaemia can lead to adverse health outcomes, so clinicians need not only to be alert to its symptoms, but to manage the consequences as well. In this article we provide a brief overview of prolactin physiology, regulation and function. We list various factors that can lead to elevated serum prolactin. We discuss the interpretation of blood results and the management of psychotropic-induced hyperprolactinaemia. We include a flow diagram to assist clinicians in decision-making in the clinical management of hyperprolactinaemia.

Learning Objectives

• Understand prolactin physiology and regulation

• Understand hyperprolactinaemia and its causes

• Know the consequences of hyperprolactinaemia and appropriately manage it in clinical practice

Clinical and radiological findings in macroprolactinemia

Hyperprolactinemia is the most common abnormality of the hypothalamic-pituitary axis. The aim of this study was to investigate the clinical and radiological features of patients with macroprolactinemia. The study population consisted of patients with elevated serum prolactin (PRL) concentrations who presented to our Endocrinology outpatient clinic. Detection of macroprolactin (macroPRL) was performed using the polyethylene glycol precipitation method. Patients in which macroPRL made up more than 60% of total PRL levels were stratified into the macroPRL group, while the remaining patients were placed in the monomeric prolactin (monoPRL) group. A total of 337 patients were enrolled with a mean age of 33.8 ± 10.8 (16-66) years and a male/female ratio of 29/308. Eighty-eight of the patients (26.1%) had an elevated macroPRL level. The mean age in the monoPRL group was higher than in the macroPRL group (35.0 ± 10.1 vs. 30.7 ± 9.8, P = 0.016). The mean PRL levels (ng/ml) in the macroPRL and monoPRL groups were similar (168.0 ± 347.0 vs. 238.8 ± 584.9, P = 0.239). Frequency of amenorrhea, infertility, irregular menses, gynecomastia, and erectile dysfunction were also similar in both groups. More patients in the macroPRL group were asymptomatic compared to the monoPRL group (30.2 vs. 12.0%, P = 0.006). Compared to the macroPRL group, the monoPRL group had a higher frequency of galactorrhea (39.2 vs. 57.1%, P = 0.04) and abnormal magnetic resonance imaging findings (65.3 vs. 81.1%, P = 0.02). Elevated macroPRL levels should be considered a pathological biochemical variant of hyperprolactinemia that may present with any of the conventional symptoms and radiological findings generally associated with elevated PRL levels.

Prevalence of pituitary adenomas in macroprolactinemic patients may be higher than it is presumed

One form of prolactin (PRL) is macroprolactin with high molecular mass. Many macroprolactinemic patients have no pituitary adenomas and no clinical symptoms of hyperprolactinemia, it is controversial whether macroprolactinemia is a benign condition that does not need further investigation and treatment. In this study, we aimed to compare macroprolactinemic patients (group I) with the true hyperprolactinemic patients (group II) for the presence of pituitary adenoma. We investigated 161 patients with hyperprolactinemia, whose magnetic resonance imaging records of the pituitary were taken. All patients were questioned for irregular menses, infertility and examined for galactorrhea. Patients were screened for macroprolactinemia by polyethylene glycol precipitation, and a recovery of ≤40% and normal monomeric PRL level was taken as an indication of significant macroprolactinemia. Of 161 patients with hyperprolactinemia, 60 (37.26%) had macroprolactinemia. PRL levels of group II were lower than those of group I (P = 0.011), although monomeric PRL levels of group II were higher than those of group I (P = 0.0005). Of 60 macroprolactinemic patients, 16 (26.7%) had pituitary adenomas. The prevalence of pituitary adenomas was lower in group I, compared with group II (P = 0.0005). No significant differences were found between the prevalences of irregular menses and infertility of group I and II (P = 0.084, P = 0.361). Prevalence of galactorrhea in group I was lower than that in group II (P = 0.048). Prevalence of pituitary adenomas in macroprolactinemic patients is lower compared with the true hyperprolactinemic patients, but may be higher than that found in other recent studies and in the general population.

The importance of measuring macroprolactin in the differential diagnosis of hyperprolactinemic patients

This study investigated the differences in clinical and laboratory features as well as treatment response in 70 outpatients with macroprolactinemia and monomeric hyperprolactinemia treated with dopamine agonists. After precipitation of the patients' serum samples with poly-ethylene-glycol (PEG), serum prolactin (PRL) levels were measured. We also measured serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol for women and testosterone for men. Clinical symptoms and signs were recorded. All patients received brain magnetic resonance imaging (MRI). After excluding patients with macroadenoma, 66 patients were treated with the dopamine agonist cabergoline. After 1 year, the clinical responses to cabergoline were recorded and PRL levels measured. Of the initial 70 patients with hyperprolactinemia, 15 patients (21.4%) were found to have macroprolactinemia, while the rest had monomeric hyperprolactinemia. The two groups did not differ with regard to galactorrhea, menstrual disturbances or impotence. There were no significant group differences in serum LH, FSH, estradiol or testosterone levels. Patients with macroprolactinemia, however, had a significantly lower infertility rate than those with true hyperprolactinemia (6.7% vs. 32.7%, p=0.005). A greater percentage of macroprolactinemic patients had normal MRI pituitary images than those with hyperprolactinemia (73.3% vs. 34.5%, p=0.029). Compared to those with true hyperprolactinemia, patients with macroprolactinemia were found to have no significant changes in clinical features and PRL levels after 1 year of cabergoline therapy (after PEG precipitation, pre- and post-PRL levels: 59.3 ± 100.2 to 13.8 ± 9.5 ng/mL vs. 6.1 ± 5.3 to 5.1 ± 4.3 ng/mL, p=0.002). In conclusion, while macroprolactinemia is a common cause of hyperprolactinemia, many clinical and laboratory features cannot be used reliably to differentiate macroprolactinemia from true hyperprolactinemia. Routine screening for all hyperprolactinemic sera with PEG might prevent the unnecessary use of image studies and medical treatments for people with hyperprolactinemia.

Cross-reactivities of macroprolactin and big-prolactin in three commercial immunoassays for prolactin: a chromatographic analysis

OBJECTIVES

To compare the recently released Elecsys Prolactin II with the Access and Centaur assays for reactivity with macroPRL, bigPRL and monomeric PRL in samples fractionated using gel filtration chromatography (GFC).

METHODS

Prolactin (PRL) concentration was measured before (total PRL) and after GFC over Superdex 75 (n=16-18) using prolactin assays on the Access2 (Beckman Coulter Inc.) and Centaur (Siemens Medical Solutions Diagnostics) analyzers and the Prolactin II assay (Roche Diagnostics) on the Elecsys 2010 analyzer. The amounts of macroPRL, bigPRL and monomeric PRL were quantified from GFC peak areas.

RESULTS

Total PRL concentrations in macroPRL-containing specimens were (means+/-SD, n=13), 842+/-496; 851+/-564 mIU/L (Access and Elecsys II, p>0.05) and 695+/-469 mIU/L (Centaur, p<0.05). Monomeric PRL (GFC peak area) was lower by the Centaur (p<0.05; Deming regression) than by the Access or Elecsys II assays. Method comparisons (Bland and Altman) therefore used PRL peak areas expressed as percent total PRL recovered after GFC. The mean differences for macroPRL and bigPRL, respectively, were (a) Elecsys PRL II-Access assay: -2.83% and -2.54% (both p<0.05); (b) Elecsys PRL II-Centaur: -1.56% (p>0.05) and -6.48% (p<0.05) and (c) Access-Centaur: 1.41% (p>0.05) and -3.95% (p<0.05).

CONCLUSION

The new Elecsys Prolactin II assay has similar cross-reaction with macroPRL and bigPRL to the Access and Centaur Prolactin assays. The differences detected were small and unlikely to have clinical impact.

Detection of molecular variants of prolactin in human serum, evaluation of a method based on ultrafiltration

BACKGROUND

In human blood, there are several molecular variants of prolactin with different biological effects. There is a need for new methods to detect and quantify these variants in order to fully understand the pathophysiological role of prolactin.

METHODS

A method based on ultrafiltration was optimized, validated and compared to PEG precipitation. Serum samples from 84 patients were analyzed before and after pre treatment on two immunoassays, Elecsys (Roche) and Access (Beckman). Protein G precipitation was used to confirm presence of macroprolactin.

RESULTS

The recovery of prolactin after ultrafiltration was lower than after PEG precipitation. A limit of 40% recovery after PEG precipitation corresponded to 27% recovery after ultrafiltration. Using these limits there were total agreement regarding detection of macroprolactin (r(s)=0.96). In contrast, recovery of prolactin in samples without macroprolactin showed a considerable disagreement between ultrafiltration and PEG precipitation (r(s)=0.48). Within-run CV was 4% for the ultrafiltration method. The correlation coefficient (r) between the immunoassays was 0.96 after ultrafiltration.

CONCLUSIONS

Ultrafiltration can be used to compare different prolactin immunoassays and to detect macroprolactin in assays with interference from PEG. For samples without macroprolactin ultrafiltration may give additional information reflecting individual variations of other molecular variants of prolactin.

Macroprolactin, big-prolactin and potential effects on the misdiagnosis of hyperprolactinemia using the Beckman Coulter Access Prolactin assay

OBJECTIVE

To examine whether use of the Beckman Coulter Access Prolactin (PRL) assay, which has low reactivity with macro-PRL, obviates the need for screening hyperprolactinemic samples.

DESIGN AND METHODS

Samples from 1020 hyperprolactinemic individuals and 401 healthy volunteers were treated with polyethylene glycol (PEG). Macro-PRL was assessed from (1) percent PRL recovery, using cut-off values derived by gel filtration chromatography (GFC) and (2) significant (p<0.05) normalisation of PRL following PEG.

RESULTS

PRL recovery was similar in volunteer and hyperprolactinemic samples (mean+/-SD 101+/-13% and 101+/-19%, respectively). In hyperprolactinemic samples, macro-PRL was identified from PRL recovery in 9.7%, although levels were moderate to high in only 3.9%. The total PRL normalised following PEG in 7.4%. Correlations of PRL recovery with the proportions of macro-, big- and monomeric PRL following GFC (n=30 samples, range of PRL and macro-PRL levels) were -0.89, -0.20 and 0.92, respectively. The big-PRL content was 0-28%. Regression analysis suggested that PEG precipitated both macro-PRL and big-PRL.

CONCLUSIONS

Using the Access assay, macro-PRL can cause apparent hyperprolactinemia and big-PRL may cause misclassification of individuals. Screening using PEG is applicable to assays with low macro-PRL reactivity provided specific reference values are derived.

Macroprolactinemia: the consequences of a laboratory pitfall

The objective of this study was to assess the prevalence of macroprolactin, a macromolecule with reduced bioactivity, in hyperprolactinemic patients. Prolactin was measured before and after precipitation of macroprolactin by polyethylene glycol in 306 patients. Only patients with prolactin values >700 mIU/L (n = 270) entered the study. In 23% of the patients, macroprolactinemia was found. In women, the occurrence of macroprolactinemia increased with advancing age (< 30 yr: 16%; 30-45 yr: 28%; > 45 yr: 42%; p < 0.05). A priori clinical signs of hyperprolactinemia (morphological abnormalities in pituitary imaging, galactorrhea infertility) occurred significantly less frequently in macroprolactinemia than in true hyperprolactinemia. In eight females macroprolactinemia and true hyperprolactinemia appeared simultaneously. To avoid diagnostic and therapeutic pitfalls, the screening for macroprolactinemia of all patients with prolactin levels of > 700 mIU/ L is recommended.

Macroprolactinemia: predictability on clinical basis and detection by PEG precipitation with two different immunometric methods

Prolactin (PRL) in human serum is present in three species: monomeric PRL (23 kDA), big PRL (50-60 kDa) and big, big PRL (bb-PRL or macroprolactinemia) of 150-170 kDa. Macroprolactin seems to be mainly composed of a molecule of monomeric PRL and an immunoglobulin G anti PRL. Its biological activity is considered low or absent, but it is measured, at various degrees, by the immunoassay method, thus causing diagnostic problems. Polyethylene Glycol (PEG) has been employed to precipitate macroprolactin, allowing its detection. This method is not applicable to all immunoassays for technical reasons. Our aim was to evaluate: 1) the predictability of macroprolactin on a clinical basis; 2) the possibility of applying PEG precipitation to Abbott AxSYM analyzer beside Roche Elecsys (already approved). We classified 34 hyperprolactinemic women, on a clinical and imaging basis, in four groups: A: functional hyperprolactinemia; B: pituitary lesions hyperprolactinemia; C: probably macroprolactinemia; D: unclassifiable hyperprolactinemia and a "control" group E of 19 healthy women. PRL was assayed, both with Elecsys and AxSYM, before and after PEG serum treatment. Eleven out of twelve group C, and 5/7 group D patients showed macroprolactinemia, against 1/7 in A and 1/8 in B. PEG was suitable for AxSYM only after the same treatment of the calibration standards, thus performing outcomes overlapping Elecsys. For clinical purposes, in the presence of macroprolactinemia, besides the recovery ratio, molar or ponderal monomeric PRL assay should be calculated.