Macroprolactinemia as a diagnostic pitfall in hyperprolactinemia: a systematic review and quantitative synthesis

CONTEXT: Macroprolactinemia is a well-recognized cause of hyperprolactinemia and an important diagnostic pitfall in endocrine practice. However, interpretation of published quantitative prolactin data remains sparse as studies vary in confirmation method, assay platform, polyethylene glycol (PEG) recovery cutoff, and reporting of prolactin measurement. EVIDENCE ACQUISITION: PubMed, Embase, Scopus, Web of Science, the Cochrane Library, and Google Scholar were systematically searched. Eligible studies reported macroprolactinemia-specific quantitative prolactin data in patients with confirmed macroprolactinemia defined by PEG precipitation, gel filtration chromatography (GFC), or both. Two reviewers independently performed study selection, data extraction, and quality assessment. Findings were summarized using study-level descriptive synthesis. The review was prospectively registered in PROSPERO and conducted in accordance with PRISMA 2020 guidelines. EVIDENCE SYNTHESIS: Forty-five studies encompassing 2853 macroprolactinemia cases from 21 413 screened patients with hyperprolactinemia across 22 countries were included. Among 33 studies eligible for primary quantitative analysis, the median study-level central total prolactin attributed to macroprolactinemia was 61.4 ng/mL ([IQR] 42.0-80.0; range 28.1-137.6), and the median study-level post-PEG monomeric prolactin was 11.7 ng/mL (IQR 8.3-13.2; range 4.0-17.0)). The median study-level maximum total prolactin was 264.5 ng/mL (IQR 97.0-425.5; range 81.8-663.0); extreme elevations were attributable to coexisting prolactinomas. CONCLUSION: In confirmed macroprolactinemia, total prolactin elevation is typically moderate, and post-PEG monomeric prolactin is usually within or near the normal range. The post-PEG monomeric prolactin value, rather than percent recovery alone, is the most informative parameter for distinguishing isolated macroprolactinemia from coexisting true hyperprolactinemia. These quantitative benchmarks may help clinicians to avoid unnecessary investigation or treatment.