Thermal degradation of polyethylene glycol 6000 and its effect on the assay of macroprolactin

Objectives: To study the effectiveness of partially degraded polyethylene glycol 6000 (PEG) as a precipitant for macroprolactin. Design and methods: PEG was heated to 63 degrees C in air for up to 20 days and its effectiveness assessed as a precipitant for sera containing normal prolactin or macroprolactin. Decomposition was studied chemically and with NMR spectroscopy. Results: Thermal degradation was similar to what had occurred over several years of natural degradation. Initially PEG degraded 2-5 days caused excess precipitation of monomeric prolactin (false-positive macroprolactinemia). Samples degraded 18-20 days failed to precipitate macroprolactin, giving false negative results. Two H-1 NMR peaks at 4-4.5 ppm were not detectable in undegraded PEG but were after 1 day. Their relative integral increased to 20 days. Conclusions: Aging of PEG can be accelerated by heating. The suitability of PEG for use in macroprolactin assays can be assessed by the absence of peaks at 4-4.5 ppm by H-1 NMR. (C) 2010 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.