Two of the authors of the Technical Brief cited above respond:

M. Fahie-Wilson makes several interesting points to which we would like to respond. First, we agree that a recovery of >65% does not indicate the absence of macroprolactin, but that macroprolactin is not the predominant form in circulation. Regarding the imprecision of the polyethylene glycol (PEG) precipitation technique, it is worth considering that the highest values were observed in the sample with a recovery in the intermediate range (47%) and in the sample with very low recovery (5%) (1). The slight differences in the PEG precipitation processes, especially those relating to temperature and centrifugation, can help to explain the differences observed when comparing our results with those of Fahie-Wilson and Soule (2). Another important point is the definition of “substantial quantities of macroprolactin”; we arbitrarily defined that >50% of the circulating prolactin in the form of macroprolactin should be considered as a substantial quantity; however, this definition obviously depends on the total prolactin present in the sample. Samples with high prolactin values and substantial quantities of macroprolactin could still have monomeric prolactin in sufficient quantities to induce clinical symptoms. As a last point, we would like to stress that the chromatographic system adopted by Fahie-Wilson and Soule (2) has a better resolution than the one that we used. Our choice of a simpler and more rapid system stems from practical necessity. Finally, we would like to add that the Fahie-Wilson and Soule publication (2) was not available during the preparation of our Technical Brief, which was very unfortunate, because access to their data would have allowed us to produce a more comprehensive publication. Nonetheless, calling attention to the macroprolactin phenomenon and providing a practical way of dealing with it are the objectives that, in our understanding, were fulfilled by the publications.