Macroprolactin in mothers and their babies: what is its origin?

OBJECTIVES

Macroprolactinemia is one of the major causes of hyperprolactinemia. The aim of this study was to clarify the origin of macroprolactin (macro-PRL).

METHODS

We examined macro-PRL in the sera of 826 pregnant women and in those of their babies' umbilical cords at delivery. Macro-PRL was evaluated by precipitation with polyethylene glycol (PEG), gel filtration chromatography (GFC), and absorption with protein G (PG).

RESULTS

We detected macro-PRL in 16 out of the 826 pregnant women (1.94 %) and in 14 of their babies, which may indicate the possibility of hereditary origin of macro-PRL. However, the macro-PRL ratios of the babies correlated positively with those of their mothers (r=0.72 for GFC, p<0.001 and r=0.77 for PG, p<0.001), suggesting that the immunoglobulin (Ig)G-type anti-PRL autoantibodies might be actively transferred to babies via the placenta and form macro-PRL by binding to their babies' PRL or PRL-IgG complexes may possibly pass through the placenta. There were two cases in which only mothers had macro-PRL, indicating that the mothers had autoantibodies that did not pass through the placenta, such as IgA, PRL bound to the other proteins or PRL aggregates. No cases were found in which only the babies had macro-PRL and their mothers did not, suggesting that macro-PRL might not arise by non-hereditary congenital causes.

CONCLUSIONS

Macro-PRL in women of reproductive age might be mostly IgG-type anti-PRL autoantibody-bound PRL. The likely origin of macro-PRL in babies is the transplacental transfer of IgG-type anti-PRL autoantibodies or PRL-IgG complexes from the mothers to their babies.

Macroprolactinemia: a mini-review and update on clinical practice

Hyperprolactinemia is common among infertile patients, with up to 15%-20% of women with oligomenorrhea having hyperprolactinemia. Suppression of the hypothalamic-pituitary-gonadal axis via inhibition of pulsatile gonadotropin releasing hormone because of hyperprolactinemia is a common endocrine etiology of infertility. There are 3 forms of human prolactin (PRL): monomeric PRL, dimeric PRL, and macro-PRL. Also known as big-big PRL, macro-PRL has a molecular weight >150 kDa and normally comprises 5%-10% of circulating PRL. When the predominant form of circulating PRL is macro-PRL, macroprolactinemia is diagnosed. Among patients with hyperprolactinemia, 10%-46% have macroprolactinemia. Patients with macroprolactinemia are at risk of unnecessary pituitary imaging and treatment with dopamine agonists if not correctly diagnosed. Given the high prevalence of macroprolactinemia among patients with elevated PRL levels and the different management of patients with macroprolactinemia vs true monomeric hyperprolactinemia, all patients with persistently elevated PRL levels should be screened for macro-PRL.

Prevalence of Macroprolactinemia in People Detected to Have Hyperprolactinemia

Background Macroprolactinemia is an analytic laboma encountered as a part of prolactin assay. No data are available on the burden of macroprolactinemia in Indians. This study aimed to determine the prevalence and predictors of macroprolactinemia among people with hyperprolactinemia.

Methods Consecutive patients detected to have serum prolactin > 18 ng/mL as per the upper reference limit were further screened for macroprolactin by post-polyethylene-glycol (PEG)-precipitation test. Macroprolactinemia was defined as post-PEG recovery of prolactin < 40%.

Results The four most common underlying etiologies for the testing of hyperprolactinemia were polycystic ovary syndrome ( n = 402; 32.71%), pituitary adenomas ( n = 318; 25.87%), drug-induced hyperprolactinemia ( n = 224; 18.23%), and infertility ( n = 126; 10.25%). A total of 1,229 patients (male:female = 191:1038) having mean age 30.46 ± 10.14 years had hyperprolactinemia, of which 168 (13.7%) were diagnosed to have macroprolactinemia. Macroprolactinemia was significantly higher in females than males (15.03 vs. 6.28%; p < 0.001). Age quartile-based analysis revealed no difference in occurrence of macroprolactinemia. Only 34 patients (2.76%) with macroprolactinemia (< 40% recovery of prolactin post-PEG precipitation) had raised prolactin levels after recovery. These patients primarily had underlying pituitary pathology.

Conclusion Macroprolactinemia is not uncommon in people being tested for hyperprolactinemia. We should not hesitate to screen for macroprolactinemia in patients who have incidentally been detected to have hyperprolactinemia.

Establishment of reference intervals of monomeric prolactin to identify macroprolactinemia in Chinese patients with increased total prolactin

BACKGROUND

Macroprolactin is responsible for pseudohyperprolactinemia and is a common pitfall of the prolactin immunoassay. We aimed to determine the frequency of macroprolactinemia in Chinese hyperprolactinemic patients using monomeric prolactin discriminated by precipitation with polyethylene glycol (PEG).

METHODS

Post-PEG monomeric prolactin gender-specific reference intervals were established for the Elecsys immunoassay method (Roche Diagnostics) using sera from healthy female (n = 120) and male (n = 120) donors. The reference intervals were validated using 20 macroprolactinemic (as assessed by gel filtration chromatography (GFC)) sera samples, and presence of monomeric prolactin was discriminated by GFC. Patients with high total prolactin were then screened by PEG precipitation to analyze macroprolactin. The demographic and biochemical details of patients with true hyperprolactinemia and macroprolactinemia were compared.

RESULTS

Reference intervals for monomeric prolactin in females and males were 3.4-18.5 and 2.7-13.1 ng/mL, respectively. Among 1140 hyperprolactinemic patients, macroprolactinemia was identified in 261 (22.9 %) patients while the other 879 (77.1 %) patients were diagnosed with true hyperprolactinemia. Menstrual disturbances were the most common clinical feature in both groups. Galactorrhea, amenorrhea, and visual disturbances occurred more frequently in true hyperprolactinemic patients (P < 0.05).

CONCLUSIONS

The prevalence of macroprolactin in Chinese patients with hyperprolactinemia was described for the first time. Monomeric prolactin concentration, along with a reference interval screening with PEG precipitation, provides a diagnostic approach for hyperprolactinemia with improved accuracy.

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.

Evaluation of autoantibodies and immunoglobulin G subclasses in women with suspected macroprolactinemia

BACKGROUND

Macroprolactin mostly composed of an immunoglobulin G (IgG) and a monomeric prolactin (PRL) represents the major circulating PRL form in the patients with macroprolactinemia that are usually asymptomatic and may not require treatment. In this study, we aimed to evaluate the prevalence of antithyroid and antinuclear antibodies, as well as the IgG subclass distributions in the patients suspected for macroprolactinemia.

METHODS

From January to July in 2018, totally 317 patients with elevated PRL were subjected to the polyethylene glycol (PEG) precipitation assay. The patients with recovery rates of ≤60% were subjected for IgG subclass determination and autoantibody testing including thyroid peroxidase antibody (aTPO), antithyroglobulin antibody (aTG), and antinuclear antibodies (ANA).

RESULTS

The higher the post-PEG PRL recovery rates, the less typical hyperprolactinemia symptoms and the higher prevalence of autoantibodies were observed. The IgG1 and IgG3 were the predominant subclasses in the PRL-IgG complexes according to the immunoprecipitation experiments.

CONCLUSION

The patients with post-PEG PRL recovery rates of <40% and 40%-60% were likely to represent two distinct populations of different clinical presentations. The prevalence of autoantibodies and IgG subclasses distribution suggested their pathogenic significance in the development of macroprolactinemia.

PCOS and Hyperprolactinemia: what do we know in 2019?

Polycystic ovary syndrome (PCOS) and hyperprolactinemia (HPRL) are the two most common etiologies of anovulation in women. Since the 1950s, some authors think that there is a pathophysiological link between PCOS and HPRL. Since then, many authors have speculated about the link between these two endocrine entities, but no hypothesis proposed so far could ever be confirmed. Furthermore, PCOS and HPRL are frequent endocrine diseases and a fortuitous association cannot be excluded. The evolution of knowledge about PCOS and HPRL shows that studies conducted before the 2000s are obsolete given current knowledge. Indeed, most of the studies were conducted before consensual diagnosis criteria of PCOS and included small numbers of patients. In addition, the investigation of HPRL in these studies relied on obsolete methods and did not look for the presence of macroprolactinemia. It is therefore possible that HPRL that has been attributed to PCOS corresponded in fact to macroprolactinemia or to pituitary microadenomas of small sizes that could not be detected with the imaging methods of the time. Recent studies that have conducted a rigorous etiological investigation show that HPRL found in PCOS correspond either to non-permanent increase of prolactin levels, to macroprolactinemia or to other etiologies. None of this recent study found HPRL related to PCOS in these patients. Thus, the link between PCOS and HPRL seems to be more of a myth than a well-established medical reality and we believe that the discovery of an HPRL in a PCOS patient needs a standard etiological investigation of HPRL.

Association of raised levels of IL-4 and anti-TPO with hyperprolactinemia

BACKGROUND AND OBJECTIVE

The modulatory role of prolactin in autoimmune regulation is well established. Hyperprolactinemia is often associated with autoimmune disease like systemic lupus erythematosus and autoimmune thyroid diseases. The objective was to compare levels of direct and indirect autoimmune factors in different categories of hyperprolactinemia cases and predict the direction of association between hyperprolactinemia and autoimmune factors, if any.

METHODS

A total of 102 hyperprolactinemia cases (>100 ng/mL serum prolactin level) were included along with 24 controls. Among 102 hyperprolactinemia cases, there were 36 idiopathic cases, 19 pituitary adenoma cases, 36 drug-induced cases, and 11 cases associated with other secondary/systemic diseases (chronic renal failure, chronic hepatic failure, etc).

MEASUREMENTS

Direct autoimmune markers, IL-2, IFN-γ, IL-4, and IL-5, were measured in serum by ELISA. Indirect autoimmune markers, anti-TPO, anti-tg, anti-CCP, VDRL, platelet count, and aPTT, were measured as per laboratory-defined protocol.

RESULTS

Serum levels of IL-4 and anti-TPO were significantly high in idiopathic hyperprolactinemia cases. Serum IL-4 levels were also significantly high in pituitary adenoma cases, drug-induced cases, and in cases with other secondary causes of hyperprolactinemia. Serum anti-TPO levels were also significantly high in drug-induced hyperprolactinemia cases.

CONCLUSION

No significant difference in autoimmune factors is observed between macroprolactinemia and true hyperprolactinemia. Serum IL-4 and anti-TPO were high in all categories of hyperprolactinemia. This suggests a possible association of hyperprolactinemia with autoimmune conditions (high IL-4 and anti-TPO), mostly subclinical. Thus, hyperprolactinemia case with serum prolactin level >100 ng/mL may require long-term follow-up for the development of autoimmune disease in future.

Serum prolactin revisited: parametric reference intervals and cross platform evaluation of polyethylene glycol precipitation-based methods for discrimination between hyperprolactinemia and macroprolactinemia

BACKGROUND

Hyperprolactinemia diagnosis and treatment is often compromised by the presence of biologically inactive and clinically irrelevant higher-molecular-weight complexes of prolactin, macroprolactin. The objective of this study was to evaluate the performance of two macroprolactin screening regimes across commonly used automated immunoassay platforms.

METHODS

Parametric total and monomeric gender-specific reference intervals were determined for six immunoassay methods using female (n=96) and male sera (n=127) from healthy donors. The reference intervals were validated using 27 hyperprolactinemic and macroprolactinemic sera, whose presence of monomeric and macroforms of prolactin were determined using gel filtration chromatography (GFC).

RESULTS

Normative data for six prolactin assays included the range of values (2.5th-97.5th percentiles). Validation sera (hyperprolactinemic and macroprolactinemic; n=27) showed higher discordant classification [mean=2.8; 95% confidence interval (CI) 1.2-4.4] for the monomer reference interval method compared to the post-polyethylene glycol (PEG) recovery cutoff method (mean=1.8; 95% CI 0.8-2.8). The two monomer/macroprolactin discrimination methods did not differ significantly (p=0.089). Among macroprolactinemic sera evaluated by both discrimination methods, the Cobas and Architect/Kryptor prolactin assays showed the lowest and the highest number of misclassifications, respectively.

CONCLUSIONS

Current automated immunoassays for prolactin testing require macroprolactin screening methods based on PEG precipitation in order to discriminate truly from falsely elevated serum prolactin. While the recovery cutoff and monomeric reference interval macroprolactin screening methods demonstrate similar discriminative ability, the latter method also provides the clinician with an easy interpretable monomeric prolactin concentration along with a monomeric reference interval.

Macroprolactinemia and Empty Sella Syndrome

Macroprolactinemia is a polymeric form of prolactin-release, causing mildly symptomatic clinical pictures. The former can be isolated or associated with other causes of hyperprolactinemia. The association with an empty sella syndrome is rare. We report a case of a female patient discovered with this association. It’s about a female patient 47 years old, followed up since the age of 31 years for bilateral galactorrhea and a spaniomenorrhea. There has been no associated drug intake. Her exploration has showed a serum prolactin level of 635 mIU/L. Thyroid test results were normal T4 = 10,2ng/L and TSH = 1.76 mIU/L. A brain scan has showed an empty sella turcica. Despite the unchanged levels of prolactinemia, the evolution under dopaminergic 5 mg /D has been marked by the occurrence of a pregnancy with persistent moderate hyperprolactinemia in the postpartum. Chromatography has showed a predominance of the macroprolactin form with: Prolactin monomer at 4.8%, Big Prolactin at 5% and Big Big Prolactin at 83%, thus stopping bromocriptine. Our observation suggests that macroprolactinemia can be associated with conventional etiologies of moderate hyperprolactinemia as the empty sella syndrome. Its detection would prevent the use of dopaminergic therapy which seems not useful.

Pituitary response profile following metoclopramide administration in women with different forms of hyperprolactinemia

AIMS

To test the hypothesis that macroprolactinemia is an extra-pituitary phenomenon by showing that the pituitary production of prolactin in patients with hyperprolactinemia due to macroprolactin is comparable to that in normoprolactinemic women and different from that in women with monomeric hyperprolactinemia.

METHODS

Twenty-five women were studied: eight with macroprolactin hyperprolactinemia, eight with monomeric hyperprolactinemia, and nine controls. Prolactin levels were measured before and after precipitation with polyethylene glycol at baseline and at 5, 10,15, 30, and 60 min after metoclopramide administration (10 mg i.v.) in the three groups.

RESULTS

The response profile of total and monomeric prolactin following the administration of metoclopramide was similar in women with monomeric hyperprolactinemia and normoprolactinemia but different in women with macroprolactinemia. The areas under the curve for total and monomeric prolactin were higher in patients with macroprolactinemia than in the other two groups (p < 0·0001). The maximal concentration of monomeric prolactin was reached before that of total prolactin in macroprolactinemic patients but the differences were not significant.

DISCUSSION

Our findings support the hypothesis that prolactin secretion is comparable in women with macroprolactinemia and in normoprolactinemic women. The dynamics of the secretion suggest that the formation of prolactin complexes is an extra-pituitary process.

A New Method of Using Polyethylene Glycol (PEG) Precipitation of Macroprolactin to Detect Genuine Hyperprolactinemia

BACKGROUND

The most commonly used method of polyethylene glycol (PEG) precipitation for macroprolactinemia (MP) screening has some significant drawbacks. The aim of this study was to establish a new method using PEG for precipitation of macroprolactin (macroPRL) to detect genuine hyperprolactinemia (genuine HP).

METHODS

The optimal PEG concentration for precipitation and the effect of PEG on the precipitation of PRL were analyzed to establish and optimize our PEG precipitation method. The PRL recovery rate and genuine HP detection rate were compared between our method and MP screening method.

RESULTS

About 25% PEG6000 was determined to be the optimal PEG concentration for precipitation. Along with an increase in protein concentration in the PRL calibration solution, the PRL recovery rate after precipitation decreased gradually. The PRL recovery rate increased when the precipitation was carried out with diluted PRL calibration solution; the recovery rate reached greater than 90% after a 5-fold dilution of the calibration solution. The genuine HP detection rate and PRL recovery rate using our diluted serum PEG precipitation method were significantly higher than those obtained with the MP screening method. Our method successfully detected 31 cases of genuine HP, which was significantly higher than the detection rate obtained using the MP screening method (25 cases; P < 0.001).

CONCLUSION

Precipitation using 5-fold diluted serum with 25% PEG6000 can effectively reduce the macroPRL concentration, increasing the PRL recovery rate and detection rate of genuine HP after precipitation, which is an effective and convenient method for the detection of genuine HP.