Purpose: Prolactin measurement is essential in endocrine diagnostics. Challenges such as the hook effect and reactivity to macroprolactin, which varies according to the reagent, complicate accurate measurement. The present study evaluated a newly marketed reagent to detect prolactin, IDS Prolactin, comparing it to an established reagent, Roche Elecsys Prolactin, assessing its behavior toward macroprolactin and polyethylene glycol (PEG) treatment, and establishing reference intervals.

Methods: The IDS Prolactin and Roche Elecsys Prolactin assays were compared using 44 samples containing macroprolactin confirmed on gel filtration chromatography (macroprolactin: BBPRL) and 104 samples for which the diagnosis of macroprolactin was excluded (monomeric prolactin: MNPRL). Analytic performance of the IDS Prolactin assay was also assessed.

Results: The new reagent showed satisfactory analytic performance, meeting EFLM standards for repeatability and intermediate imprecision. Comparison between the two methods found robust correlation for monomeric samples (y=1.060x-18.28; r2=0.993). Compared to the Roche assay, which is particularly low in its reaction to macroprolactin, the IDS assay displayed a higher level of detection. PEG precipitation effectively separated monomeric and macroprolactin samples when a cut-off of 65% recovery was used or at the threshold of 444 mIU/L (20.9 µg/L) for post-PEG monomeric prolactin upper limit of normal. Reference intervals were established for women, with ROC curve analysis demonstrating high sensitivity and specificity.

Conclusion: The IDS Prolactin assay showed excellent analytic performance and satisfactory characteristics on macroprolactinemic samples.