Certification strategies for health-related SRMS at NIST

Abstract

Inaccuracy in health-related measurements raises overall health care costs, results in misdiagnoses, leads to inaccurate conclusions in clinical studies, and results in inaccurate nutrition labeling. NIST has an extensive program aimed at providing the health measurements community with standard reference materials (SRMs) to assist them in making accurate measurements. A variety of approaches are used to certify health-related SRMs. For pure crystalline SRMs used as primary standards, direct assays of purity are often not possible. Thus numerous techniques including differential scanning calorimetry, mass spectrometry, chromatography, 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 capabilities. When accuracy needs are the highest and the methods exist, NIST uses definitive methods, primarily involving isotope dilution mass spectrometry. These methods have been applied to the certification of serum-based SRMs for a number of the common clinical analytes. For many analytes, definitive methods have not been developed, so NIST uses other strategies 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 outside laboratories having extensive experience with a particular analysis. The paper includes tables with examples of many of the health-related SRMs that are available.