Received: 24 April 2002 Accepted: 11 July 2002 Presented at GLOBAL ODYSSEY 2002 – International Conference on Proficiency Testing/External Quality Assessment for Medical Laboratories, 24–26 February 2002, Atlanta, GA, USA Abstract Proficiency testing and external quality assurance of medical laboratories is now entering its sixth decade. These activities comprise a broad range of applications includ- ing: providing participants and pub- lic health authorities with estimates of measurement uncertainty and na- tional infrastructure; providing edu- cation; provision of a practical basis for accreditation and regulatory com- pliance. All branches of medical lab- oratory science have employed ex- ternal quality assurance as a basis for improvement and comparability. The opportunities and challenges re- viewed here include: the proper es- tablishment of multiple target values in comparison to a system of trace- ability to reference or definitive methods; the problems of matrix ef- fects and commutability of patient and proficiency test samples; gener- ating information on laboratory in- frastructure and trends in analytical technique and performance; provid- ing education and setting goals for laboratory improvement; problems of specimen distribution; application of Internet technology; the role of programs in legal mandates and ac- creditation. Keywords Medical laboratories · Proficiency testing · Interlaboratory comparisons · Review Accred Qual Assur (2002) 7:335–340 DOI 10.1007/s00769-002-0513-8 © Springer-Verlag 2002 REVIEW PAPER Robert Rej Proficiency testing and external quality assurance: crossing borders and disciplines Introduction Although it has a foundation dating back centuries, labo- ratory medicine is a relatively young discipline that be- came established at the dawn of the twentieth century. Only through biomedical research after the Second World War were modern clinical laboratories established [1]. External quality assurance and proficiency testing have been integral to modern medical laboratories al- most from the outset. Unlike many developments in medicine and biological science, external quality assess- ment of medical laboratories did not evolve from the work of many sequential studies, but rather emerged – nearly fully-formed – from the seminal work of Belk and Sunderman [2]. Dr. Sunderman (Fig. 1) subsequently en- joyed a greater than 50 year distinguished career in the area of improvement of medical laboratories [3] and he recently celebrated his 103rd birthday. The model used by Belk and Sunderman over half a century ago for he- matology and clinical chemistry is still very much in use and remains a mainstay for nearly all laboratory im- provement, accreditation, and regulatory proficiency testing programs [3, 4]. Indeed, external quality assurance programs for medi- cal laboratories have components related to the technical performance of individual laboratories, education, regu- latory compliance, accreditation, traceability of analyti- cal techniques, and an overall assessment of the disci- pline. Increasing numbers of scientific publications each year relate to proficiency testing of medical laboratories (Fig. 2). Assessment schemes run the gamut from those of sperm morphology [5] to molecular detection and quantitation of hepatitis B virus DNA [6]; from special- ized focused programs (e.g., glycohemoglobin [7]) to R. Rej Laboratory of Molecular Diagnostics, Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany, NY 12201, USA e-mail: bob@wadsworth.org R. Rej Department of Biomedical Sciences, School of Public Health, State University of New York, Albany, NY 12201, USA