Extensive Experience and Validation of Polyethylene Glycol Precipitation as a Screening Method for Macroprolactinemia

Serum human prolactin (PRL) is heterogeneous in molecular size, with the 23-kDa monomer being the predominant form in healthy subjects and patients with prolactinomas. From the point of view of molecular size, other circulating forms include the 50-kDa dimer (big-PRL) and the 150- to 170-kDa form (big-big-PRL, or macroprolactin) (1). Recent publications have associated asymptomatic hyperprolactinemia with a predominance of macroprolactin in the circulation; this occurrence appears to be more common than previously thought (2)(3)(4) and can have obvious practical implications. The finding of a predominance of macroprolactinemia can change the focus of the evaluation of a patient, with the possible avoidance of more sophisticated and expensive imaging studies. We evaluated the polyethylene glycol (PEG) precipitation method to screen for the presence of macroprolactinemia in a large series of clinical samples. Serum PRL was measured by immunofluorometric assay (IFMA; reference range, 2–15 μg/L; Delfia, Wallac Oy), and samples with values ≥30 μg/L were studied. The value of 30 μg/L or higher, considered as …