Quality control of estrogen receptor assays in the Netherlands

Summary Lyophilized receptor-positive tissue powders and cytosols, prepared from calf uterus and human breast tumor tissue, are used to assess the validity of routine dextran-coated charcoal estrogen receptor assays. Since 1978 lyophilized reference preparations have been analyzed twice yearly by 18 laboratories in the Netherlands. During 8 consecutive trials 20 different lyophilized samples were studied. The inter-laboratory variability of estrogen receptor results decreased with time. Most laboratories found receptor values around the median value of all groups together, though some participants consistently reported estrogen receptor values that were higher or lower than the median. The variability of estrogen receptor results between labs seemed to be associated with cytosol dilution, determination of non-specific binding, concentration and volume of dextrancoated charcoal, and the use of single dose assays or Scatchard analysis. The agreement on the presence or absence of estrogen receptors was more than 98% for lyophilized reference samples with high receptor content. For samples with low receptor content 85% agreement was observed, while 12% of the assays performed on receptor-negative material were reported to be estrogen receptor-positive. The use of the same protein determination (Coomassie Brilliant Blue) and human serum albumin standard has decreased the interlaboratory variation coefficient of the protein results to 7.5%. Address for reprnts: A. Koenders, Dept. of Experimental and Chemical Endocrinology, St. Radboud Hospital, Geert Grooteplein Z 8, 6500 HB Nijmegen, the Netherlands List of participating laboratories and institutions: Hospital de Lichtenberg, Amersfoort; Antoni van Leeuwenhoek Hospital, Amsterdam; Foundation Medical Laboratories, Breda; Foundation of Cooperative Hospitals Delft (SSDZ), Delft; Catharina Hospital, Eindhoven; Hospital de Stadsmaten and Ziekenzorg, Enschede; Academic Hospital, Groningen; The Wever Hospital, Heerlen; Laboratory of Public Health, Leeuwarden; Department of Pathological Chemistry, Academic Hospital, Leiden; Department of Experimental and Chemical Endocrinology, Sint Radboud Hospital, Nijmegen; Scientific Development Group Organon International B.V., Oss; Department of Biochemistry II, Erasmus University Rotterdam, Rotterdam; Rotterdam Radio-Therapeutic Institute/ Dr Daniel den Hoed Clinic, Rotterdam; Institute of Oncology Dr Bernard Verbeeten, Tilburg; Department of Endocrinology, Academic Hospital, Utrecht; Laboratory for Nuclear Medicine Voorburg, Vught; Sophia Hospital, Zwolle.