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

Epidemiological and clinical profiles of Saudi patients with hyperprolactinemia in a single tertiary care center

BACKGROUND

Prolactin is a hormone of the pituitary gland whose main function is the production of milk. Hyperprolactinemia is defined as an increase in prolactin levels above 25 μg/L in women and 20 μg/L in men. Causes of hyperprolactinemia include pituitary tumors, especially prolactinomas. Hyperprolactinemia can manifest clinically with a variety of symptoms, including galactorrhea and menstrual irregularities in women and erectile dysfunction in men. There are limited data on the epidemiology of hyperprolactinemia in the Middle East region.

OBJECTIVES

Description of the epidemiology and clinical features of hyperprolactinemia in a cohort from Saudi Arabia.

DESIGN

Medical record review SETTING: Tertiary medical center in Riyadh PATIENTS AND METHODS: The study included adult patients with hyperprolactinemia in King Abdulaziz Medical City in Riyadh. The patients were treated in endocrinology clinics from 2015 to 2019. Patients of both sexes older than 14 years were enrolled in the study. Patients with insufficient follow-up were excluded. Data were collected on demographic characteristics, symptoms, prolactin level, cause of high prolactin level, and treatment.

MAIN OUTCOME MEASURES

The frequency of different etiologies and symptoms in patients with hyperprolactinemia.

SAMPLE SIZE

295 patients RESULTS: The majority of patients with hyperprolactinemia were female 256 (86.8%). Hyperprolactinemia was diagnosed more frequently in patients in the age groups 21-30 years (42.6%) and 31-40 years (24.1%). The majority of the study population was obese or overweight: 136 (46.3%) and 74 (25.2%), respectively. Most of the cases were symptomatic (192, 65.1%). In women, the most common symptom was oligomenorrhea (35%). In men, infertility and erectile dysfunction were the most common clinical symptoms (50% and 44.7%, respectively). Idiopathic causes were the most common etiology (108, 36.6%), followed by pituitary adenomas (81, 27.5%). The majority of patients were treated (184,62.4%), with cabergoline being the most commonly used medication (173, 94.0%).

CONCLUSION

The demographic and clinical presentations and causes of hyperprolactinemia in male and female Saudi patients were similar to that in studies in other populations.

LIMITATIONS

Single-center retrospective chart review study.

CONFLICT OF INTEREST

None.

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.

Macroprolactin: an overlooked reason of hyperprolactinemia

Background

Immunoassays show variability in the detection of macroprolactin. The aim of this study was to detect the frequency of macroprolactinemia in hyperprolactinemic patients and the problems encountered in routine clinical practice.

Methods

The screening of macroprolactinemia was performed by precipitation with polyethylene glycol (PEG) in 900 patient samples with hyperprolactinemia over a period of approximately 6 months. Recovery values of less than 40% and greater than 60% were considered as macroprolactinemia and predominantly monomeric prolactin (PRL), respectively.

Results

A total of 900 (17.9%) of the 5007 PRL results were out of reference range. Thirty-one (3.4%) of the patients had less than 40% recovery after screening of all patients with hyperprolactinemia. However, the macroprolactin test was requested by clinics from only 171 patients and seven of these patients had less than 40% recovery. We also detected predominantly macroprolactin in 24 samples, overlooked in routine practice. The patients with PRL above 100 ng/mL had no macroprolactinemia.

Conclusions

The screening for macroprolactinemia of hyperprolactinemic patients who have <100 ng/mL and also with unexplained hyperprolactinemia should be the first approach before any further research or treatment is initiated. Thus, unnecessary test repetition, investigation and inappropriate treatment can be avoided. Each laboratory should inform clinicians about the frequency of macroprolactinemia.

Cardiometabolic Risk Factors in Men with Elevated Macroprolactin Content: A Pilot Study

BACKGROUND

Macroprolactinemia is a condition associated with the presence of large amounts of high molecular weight complexes of prolactin. Despite high prevalence, clinical significance of macroprolactin remains poorly understood.

OBJECTIVE

The aim of this study was to assess cardiometabolic risk in men with isolated macroprolactinemia.

METHODS

The study population included 11 men with isolated macroprolactinemia, 14 subjects with monomeric hyperprolactinemia and 14 men with prolactin levels within the reference range. Glucose homeostasis markers, plasma lipids, as well as plasma levels of uric acid, high-sensitivity C-reactive protein (hsCRP), fibrinogen, homocysteine and 25-hydroxyvitamin D were determined in all included patients.

RESULTS

Compared to healthy counterparts, men with isolated macroprolactinemia had higher levels of 2-h postchallenge glucose, hsCRP and fibrinogen, lower levels of 25-hydroxyvitamin D and reduced insulin sensitivity. Patients with monomeric hyperprolactinemia were characterized by increased plasma levels of 2-h postchallenge glucose, triglycerides, uric acid, hsCRP, fibrinogen and homocysteine, reduced insulin sensitivity and decreased plasma concentrations of HDL cholesterol and 25-hydroxyvitamin D. Subjects with isolated macroprolactinemia differed from patients with monomeric hyperprolactinemia in postchallenge plasma glucose, insulin sensitivity, uric acid, hsCRP, fibrinogen, homocysteine and 25-hydroxyvitamin D. In men with monomeric hyperprolactinemia, uric acid, hsCRP, fibrinogen, homocysteine and 25-hydroxyvitamin D, while in men with elevated levels of macroprolactin, uric acid, hsCRP, fibrinogen and 25-hydroxyvitamin D correlated with a content of monomeric prolactin or macroprolactin, respectively, as well as with a degree of insulin sensitivity.

CONCLUSIONS

The obtained results suggest that macroprolactinemia may increase cardiometabolic risk but to a lesser extent than monomeric hyperprolactinemia.

Laboratory and clinical significance of macroprolactinemia in women with hyperprolactinemia

The role of macroprolactinemia in women with hyperprolactinemia is currently controversial and can lead to clinical dilemmas, depending upon the origin of macroprolactin, the presence of hyperprolactinemic symptoms and monomeric prolactin (PRL) levels. Macroprolactinemia is mostly considered an extrapituitary phenomenon of mild and asymptomatic hyperprolactinemia associated with normal concentrations of monomeric PRL and a predominance of macroprolactin confined to the vascular system, which is biologically inactive. Patients can therefore be reassured that macroprolactinemia should be considered a benign clinical condition, resistant to antiprolactinemic drugs, and that no diagnostic investigations or prolonged follow-up should be necessary. However, a significant proportion of macroprolactinemic patients appears to suffer from hyperprolactinemia-related symptoms and radiological pituitary findings commonly associated with true hyperprolactinemia. The symptoms of hyperprolactinemia are correlated to the levels of monomeric PRL excess, which may be explained as coincidental, by dissociation of macroprolactin, or by physiological, pharmacological and pathological causes. The excess of monomeric PRL levels in such cases is of primarily importance and the diagnosis of macroprolactinemia is misleading or inadequate. However, macroprolactinemia of pituitary origin associated with radiological findings of pituitary adenomas may rarely occur with similar hyperprolactinemic manifestations, exclusively due to bioactivity of macroprolactin. Therefore, in such cases with hyperprolactinemic signs and pituitary findings, macroprolactinemia should be considered a pathological biochemical condition of hyperprolactinemia. Accordingly, individualized diagnostic investigations with the introduction of dopamine agonists, or other treatment with prolonged follow-up, should be mandatory. The review analyses the laboratory and clinical significance of macroprolactinemia in hyperprolactinemic women suggesting clinically useful diagnostic and treatment strategies.

Impact of macroprolactin on galactorrhea and the rate of patients possibly affected by macroprolactin

The clinical influence of macroprolactin (MPRL) is not clearly understood and the rate of patients potentially affected by MPRL is unknown. We investigated the influence of MPRL on the onset of galactorrhea and estimated the rate of patients with a proportion of MPRL fraction that may possibly affect galactorrhea. Data of patients with obstetric or gynecological symptoms who had undergone PRL fractionation testing were retrospectively analyzed. To evaluate factors influencing galactorrhea, a multivariate logistic regression analysis was performed and the adjusted odds ratios of MPRL for galactorrhea were calculated. Cutoff values for the total PRL level and the proportion of MPRL fractions for galactorrhea were determined by ROC analysis using a multivariate logistic model. The prevalence of patients with a proportion of MPRL fraction greater than or equal to the cutoff value for galactorrhea was estimated. The median proportion of MPRL fraction was 30.1% and increased as PRL level increased. Total PRL and MPRL had a significant influence on the onset of galactorrhea and the adjusted odds ratio was 1.09 in total PRL and 0.94 in MPRL. The rate of patients with a proportion of MPRL fraction that may possibly affect galactorrhea was estimated to be 33.5% of the study population, and thus found to be twelve times or more the number of macroprolactinemia patients. Future prospects for hyperprolactinemia may require diagnostic criteria using free prolactin levels and so MPRL fraction measurement is important for the diagnosis and treatment of patients with obstetric and gynecological symptoms.

Hyperprolactinaemia in male infertility: Clinical case scenarios

Objective

To explore the evaluation, treatment and impact of hyperprolactinaemia on male infertility and testicular function, as hyperprolactinaemia is commonly detected during the evaluation of infertile men.

Methods

A literature search was performed using MEDLINE/PubMed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to identify all studies exploring hyperprolactinaemia in male infertility.

Results

Elevated levels of serum prolactin have a detrimental effect on male reproduction through inhibition of the pulsatile release of gonadotrophins from the anterior pituitary gland, and a direct effect on spermatogenesis. Treatment of confirmed hyperprolactinaemia with dopamine agonists leads to significant improvements in both semen parameters and hormone levels.

Conclusion

Hyperprolactinaemia, both directly and indirectly, has a negative effect on sperm production, and its detection and management in men seeking fertility is mandatory.

Sexual function and depressive symptoms in young women with elevated macroprolactin content: a pilot study

Elevated prolactin levels seem to be associated with impaired sexuality. The clinical significance of macroprolactinemia, associated with the predominance of high molecular mass circulating forms of prolactin, is still poorly understood. This study was aimed at investigating sexual function in young women with macroprolactinemia. The study enrolled 14 young women with macroprolactinemia, 14 with increased monomeric prolactin levels, as well as 14 age- and weight-matched healthy women. All patients completed a questionnaire evaluating female sexual function (Female Sexual Function Index-FSFI), as well as a questionnaire assessing the presence and severity of depressive symptoms (Beck Depression Inventory Second Edition-BDI-II). Apart from total prolactin levels and macroprolactin content, circulating levels of thyrotropin, total testosterone, and 17-β estradiol were also measured. Patients with elevated monomeric prolactin levels had a lower total FSFI score, as well as lower scores for all domains: sexual desire, sexual arousal, lubrication, orgasm, sexual satisfaction, and dyspareunia. These scores correlated with total and monomeric prolactin levels. In turn, women with macroprolactinemia were characterized by a lower score for sexual desire, and only this score correlated with total prolactin levels and macroprolactin content. The total score in the BDI-II questionnaire was higher in patients with hyper- and macroprolactinemia than in the control subjects. Contrary to multidimensional impairment of sexual function in women with elevated monomeric prolactin, macroprolactinemia only seems to disturb sexual desire.

A neutral effect of testosterone therapy on macroprolactin content in men with macroprolactinemia and late-onset hypogonadism

BACKGROUND

In the light of recent studies, macroprolactinemia seems to occur much more frequently than previously thought. In women, oral contraceptive pills exhibit a stimulatory effect on macroprolactin production. No previous study has investigated macroprolactin levels in androgen-treated hypogonadal men.

METHODS

We studied 10 men with isolated macroprolactinemia and 14 men with normal prolactin levels who because of late-onset hypogonadism were treated with intramuscular testosterone enanthate. Serum prolactin, macroprolactin content, serum testosterone and gonadotropin levels were assessed at baseline and after 4 months of therapy.

RESULTS

Although baseline levels of testosterone and gonadotropins were similar in men with and without macroprolactinemia, clinical symptoms were more severe in patients with elevated big-big prolactin levels. As expected, testosterone treatment increased serum testosterone, slightly reduced serum gonadotropins, as well as improved clinical condition in both patients with and without macroprolactinemia, with no difference between the groups. However, testosterone therapy did not affect serum prolactin and macroprolactin content, even after replacing intramuscular testosterone enanthate with oral testosterone undecanoate.

CONCLUSIONS

Our results suggest a negligible effect of testosterone replacement on macroprolactin levels in macroprolactinemic men with late-onset hypogonadism.

Challenges and pitfalls in the diagnosis of hyperprolactinemia

The definition of the etiology of hyperprolactinemia often represents a great challenge and an accurate diagnosis is paramount before treatment. Although prolactin levels > 200-250 ng/mL are highly suggestive of prolactinomas, they can occasionally be found in other conditions. Moreover, as much as 25% of patients with microprolactinomas may present prolactin levels < 100 ng/mL, which are found in most patients with pseudoprolactinomas, drug-induced hyperprolactinemia, or systemic diseases. On the other hand, some conditions may lead to falsely low PRL levels, particularly the so-called hook effect, that is an assay artifact caused by an extremely high level of PRL, and can be confirmed by repeating assay after a 1:100 serum sample dilution. The hook effect must be considered in all patients with large pituitary adenomas and PRL levels within the normal range or only modestly elevated (e.g., < 200 ng/mL). An overlooked hook effect may lead to incorrect diagnosis and unnecessary surgical intervention in patients with prolactinomas. Another important challenge is macroprolactinemia, a common finding that needs to be identified, as it usually requires no treatment. Although most macroprolactinemic patients are asymptomatic, many of them may present galactorrhea or menstrual disorders, as well as neuroradiological abnormalities, due to the concomitance of other diseases. Finally, physicians should be aware that pituitary incidentalomas are found in at least 10% of adult population.