Cross-reactivities of macroprolactin and big-prolactin in three commercial immunoassays for prolactin: A chromatographic analysis

Objectives: To compare the recently released Elecsys Prolactin II with the Access and Centaur assays for reactivity with macroPRL, bigPRL and monomeric PRL in samples fractionated using gel filtration chromatography (GFC). Methods: Prolactin (PRL) concentration was measured before (total PRL) and after GFC over Superdex 75 (n = 16–18) using prolactin assays on the Access2 (Beckman Coulter Inc.) and Centaur (Siemens Medical Solutions Diagnostics) analyzers and the Prolactin II assay (Roche Diagnostics) on the Elecsys 2010 analyzer. The amounts of macroPRL, bigPRL and monomeric PRL were quantified from GFC peak areas. Results: Total PRL concentrations in macroPRL-containing specimens were (means ± SD, n = 13), 842 ± 496; 851 ± 564 mIU/L (Access and Elecsys II, p > 0.05) and 695 ± 469 mIU/L (Centaur, p < 0.05). Monomeric PRL (GFC peak area) was lower by the Centaur (p < 0.05; Deming regression) than by the Access or Elecsys II assays. Method comparisons (Bland and Altman) therefore used PRL peak areas expressed as percent total PRL recovered after GFC. The mean differences for macroPRL and bigPRL, respectively, were (a) Elecsys PRL II–Access assay: − 2.83% and − 2.54% (both p < 0.05); (b) Elecsys PRL II–Centaur: − 1.56% (p > 0.05) and − 6.48% (p < 0.05) and (c) Access–Centaur: 1.41% (p > 0.05) and − 3.95% (p < 0.05). Conclusion: The new Elecsys Prolactin II assay has similar cross-reaction with macroPRL and bigPRL to the Access and Centaur Prolactin assays. The differences detected were small and unlikely to have clinical impact.