Two-site in-house quality control for estrogen receptor (ER) assay

Abstract

As no external Quality Control Program has existed for ER assay since 1988, and commercial preparations are either unsuitable or expensive, a local QC program was set up between our hospitals. An ovarian tumour with high levels of ER was obtained. Cytosol was prepared, aliquoted into Nunc cryotubes and stored at -70°C. This material has been used in each ER assay (Abbott ER-EIA) at both the hospitals since January 1989. Mean cytosol ER values have not changed significantly over a 2.5 year period (see table). The difference in results between the laboratories was primarily due to different methods of proteins estimation. Mean intra-assay coefficients of variation (CV) were 2.1% and 4.8% for RWH and RMH respectively.RWHRMHNMEANSDCVNMEANSDCV1989 RESULTS378513154011728241990 RESULTS409918173810820181991 RESULTS19105131324140139.4 The cytosol preparation, although stable when frozen, was quite heat labile. It showed partial loss of activity after 10 minutes at room temperature, and total loss of activity after 30 minutes at 37°C. If stored at -70°C, it remains stable over at least two years, and provides a suitable cheap source of QC material. It, however, does not address the issue of inter-hospital error introduced in the homogenisation process.