Endocrine Abstracts

Issue: Macroprolactin (MPRL) is a high molecular mass complex of prolactin with minimal bioactivity in vivo that may be the cause of elevated serum prolactin (PRL) as determined by immunoassay. Unrecognised macroprolactinemia can lead to misdiagnosis and mistreatment. The frequency of MPRL is highly dependent on the affinity of the antibody used in the assay.

The aim of this study: Was to compare the frequency and quantity of MPRL measured by a first and second-generation prolactin assay.

Methods: 109 sera sent for PRL estimation were analysed: PRL was measured both in the native sera and after PEG-precipitation by a first and second-generation electrochemiluminscence immunoassay (ECLMA1 and ECLMA2, Elecsys 2010, Roche).

Results: The mean PRL concentration was lower if measured by ECLMA2 (961±687 versus 1419±1079 IU/l, P<0.001). The rate of elevated PRL was 59% by ECLMA1 and 51% by ECLMA2 respectively. The mean recovery following PEG-precipitation was not different (89±23 and 89±15), but the rate of macroprolactinemia defined (as less than 40% recovery) was 10-times more often by ECLMA1 (N=19) than ECLMA2 (N=2). Normalisation of elevated PRL levels after PEG precipitation occurred in 10% (N=11) and 12% (N=12), respectively of the sera with not difference according to the method used and typically in cases with slight hyperprolactinemia.

Conclusion: The affinity of the second-generation ECLMA2 assay to MPRL seems to be less than that of the first generation assay. Approximately 8% less cases of macroprolactinemia are to be expected by the novel assay even is the normal “cut off” level of PRL is decreased from 700 to 500 IU/l. The dramatic decrease of cases with less than 40% recovery raises the proposition that instead of %-recovery the normalisation of the PRL concentration following PEG precipitation should be used to define cases with macroprolactiemia.