Isotope dilution mass spectrometry and the National Reference System.

The clinical laboratory community of the United States, which is well represented by the NRSCL/NCCLS, has endorsed the IDMS/DMs developed at NIST. These DMs provide the accuracy (true value) base for the U.S. National Reference System for a number of specific analytes in human serum. Fortunately, the U.S. government through (a) actions of NIST administrators and scientists, (b) financial support from NIH (NIGMS) and FDA, and (c) interagency agreements with CDC has accepted the responsibility for developing and maintaining IDMS/DMs for clinically important analytes as an essential part of this national measurement system infrastructure. Furthermore, it is important to note that several professional organizations, particularly, The American Association for Clinical Chemistry (AACC) and The College of American Pathologists (CAP), have interacted heavily with NIST in full support of these national standardization activities. CAP supports three full-time Research Associates at NIST so that target values on serum samples used in its Interlaboratory Comparison Survey Programs may be traced to DMs. This remarkable cooperation and teamwork between government agencies and private sector organizations, as well as numerous individual scientists and physicians, which promotes greater accuracy of patient results, depends heavily upon the continued timely availability of IDMS/DM measurements. In short, NIST's value assignments on human serum samples (e.g., SRMs and materials for CLIA '88 proficiency testing programs) by this critical IDMS/DM metrology provide the pragmatic base for assuring accurate test results in medicine. The resources required to support IDMS/DM technology at NIST over many decades are not trivial and from time to time require renewed R&D efforts to upgrade methodology and recapitalization in mass spectrometry instrumentation.