Prolactin Assay Interference by Macroprolactin.

Background: Macroprolactinemia is a common presentation especially in gynecology and fertility clinics. However, with this clinical condition, there is a potential for misdiagnosis and unnecessary investigations/treatments due to lack of awareness of its prevalence and diagnostic approaches amongst trainees and physicians.

Methods: In this paper, we discuss the causes of hyperprolactinemia, its pathobiology, and an approach to macro-prolactinemia including relevant clinical chemistry methods and their limitations through the case of a 45-year-old female with a history of irregular menstrual cycles, who was seen in the endocrine clinic.

Results: Patient did not have a history of infertility, galactorrhea, visual-disturbance, or headaches. Her physical examination and routine clinical chemistry investigations were unremarkable. Her initial prolactin level was 4,836 mIU/L (109 - 557) with subsequent results demonstrating diminishing levels of prolactin a month apart (1,023 mIU/L). Polyethylene glycol (PEG) precipitation test demonstrated the presence of macroprolactin with a 3% post-PEG recovery of prolactin and 111 mIU/L post-PEG prolactin concentration.

Conclusions: Patient's post-PRL results and clinical course confirmed the presence of macroprolactin to be the cause of factitious hyperprolactinemia. A sound approach to macroprolactinemia is critical in clinical and laboratory practices.