Acs:180 Results Obtained for Macroprolactinemic Samples Multiplexed Mutagenically Separated Pcr: Simulta- Neous Single-tube Detection of the Factor V R506q (g1691a), the Prothrombin G20210a, and the Methyl- Enetetrahydrofolate Reductase A223v (c677t) Variants

(range, 250% to 86%) indicates a highly variable, sampledependent response of the ACS:180 assay to macroprolactin. The great disparity of values observed when comparing results from macroprolactinemic samples measured by the Elecsys or the Immulite assay with the results obtained by a low-reading method such as ACS:180 may reflect variation in the structure of macroprolactin. Macroprolactin is most probably not one unique macromolecule but rather a heterogeneous family of PRL-IgG complexes that react differently depending on the type of immunoassay used for PRL determination. In conclusion, our study reinforces the point that PRL assays from different manufacturers give highly variable prolactin results for samples containing macroprolactin (4–8). Our data additionally show that the reactivity of macroprolactin in a PRL immunoassay, be it a low-, medium-, or high-reading method, is not identical for all macroprolactinemic samples. This finding underscores the necessity of a systematic screening strategy for macroprolactin in all samples with increased PRL (4, 5, 10, 11). With the Elecsys PRL assay, PEG precipitation, with a cutoff value of 50%, was an efficient and easy-to-use screening tool for the presence of macroprolactin. Because of the interference of PEG in some commercially available PRL assays, the confirmation of macroprolactinemia may require time-consuming methods, such as centrifugal ultrafiltration (9 ) and GFC. We thank Michael N. Fahie-Wilson, Department of Clinical Chemistry, Southend Hospital, Westcliff-on-Sea, Essex, UK, for expert advice.