Macroprolactinoma hook effect — SCE Endocrinology MCQ

Correct answer: D — Serially diluted prolactin measurement for the hook effect

The best answer is “Serially diluted prolactin measurement for the hook effect”. Very high prolactin can saturate both capture and signal antibodies in a sandwich assay, producing an artefactually modest result; dilution reveals the true concentration and can prevent unnecessary surgery. “Measure calcitonin to determine whether the lesion secretes prolactin” is less appropriate because calcitonin is a C-cell marker and does not address prolactin assay behaviour “Accept the prolactin result because modern immunoassays cannot saturate” is less appropriate because high-dose hook effects remain a recognised immunoassay limitation “Start levothyroxine as a diagnostic challenge” is less appropriate because thyroid replacement does not diagnose a secretory pituitary macroadenoma “Use an oral glucose tolerance test as the definitive prolactinoma test” is less appropriate because glucose suppression testing assesses growth-hormone excess rather than prolactin secretion

Reference: Pituitary Society international consensus statement on prolactinoma. https://www.nature.com/articles/s41574-023-00886-5