Polyethylene glycol precipitation as a screening method for macroprolactinemia.

Vieira et al. (1) used the Wallac Delfia immunofluorometric assay to demonstrate that macroprolactin is a common cause of apparent hyperprolactinemia, and this confirms our experience (2) and that of others (3). However, their data validating the polyethylene glycol (PEG) precipitation as a screening method for detecting macroprolactinemia are substantially different than ours (2) and appear to be inconsistent. They suggest that a recovery of >65% of serum prolactin (PRL) after PEG precipitation indicates the absence of macroprolactin; however, their Fig. 1⇓ shows that samples giving such recoveries contained 10–40% high-molecular weight PRL as determined by gel filtration chromatography. Furthermore, the data shown in Fig. 1⇓ of the recovery of PRL after PEG precipitation and the proportion of PRL present as the high-molecular …