CERTIFICATION STRATEGIES FOR HEALTH-RELATED SRMS AT NIST

Inaccuracy in health-related measurements raises overall health care c osts, results in misdiagnoses, leads to inaccurate conclusions in clin ical studies, and results in inaccurate nutrition labeling. NIST has a n extensive program aimed at providing the health measurements communi ty with standard reference materials (SRMs) to assist them in making a ccurate measurements. A variety of approaches are used to certify heal th-related SRMs. For pure crystalline SRMs used as primary standards, direct assays of purity are often not possible. Thus numerous techniqu es including differential scanning calorimetry, mass spectrometry, chr omatography, and others may be used to assess purity. For matrix SRMs used to assess the accuracy of measurement systems, the approaches for certification depend upon the needs of the users and NIST capabilitie s. When accuracy needs are the highest and the methods exist, NIST use s definitive methods, primarily involving isotope dilution mass spectr ometry. These methods have been applied to the certification of serum- based SRMs for a number of the common clinical analytes. For many anal ytes, definitive methods have not been developed, so NIST uses other s trategies for certification. In some cases, such as for drugs of abuse , two independent methods are used for the measurements. For nutrients such as vitamins, in-house methods are used along with results from o utside laboratories having extensive experience with a particular anal ysis. The paper includes tables with examples of many of the health-re lated SRMs that are available.