Development of Reference Methods and Reference Materials for Clinical Diagnostic Markers

The accuracy of clinical diagnostic measurements is essential for reliable diagnosis and cost-effective treatment of disease. NIST's involvement in reference methods and reference materials to support accuracy in health-related measurements began more than forty years ago, and NIST is continually expanding the range of SRMs available. NIST works closely with the in-vitro diagnostic (IVD) community to identify and address reference material and methods needs, and to ensure that these SRMs are commutable with routine clinical assays. As part of this effort, new higher-order analytical methods have also been developed. These new reference methods and the associated SRMs provide critical traceability to the IVD industry and help improve the reliability of routine clinical measurements.

Reference measurement procedures and standard reference materials help ensure accuracy and comparability of routine clinical assays. In addition, this work allows U.S. clinical diagnostic manufacturers to comply with the European Union directive regarding in-vitro diagnostic medical devices (IVD MD), which requires that values assigned to calibrators and control materials be traceable to reference materials and reference measurement procedures of a higher order. The Joint Committee for Traceability in Laboratory Medicine (JCTLM) maintains a listing of these higher-order reference materials and methods. The SRMs also support accuracy in measurements performed as part of the National Health and Nutrition Examination Survey (NHANES) that is conducted by CDC.

NIST continually updates its portfolio of SRMs for clinical diagnostics to meet the needs of the clinical chemistry community. Listed below are materials that are currently available. Early serum-based SRMs for clinical diagnostics were lyophilized materials. NIST is now moving toward fresh-frozen matrices because these materials are anticipated to have improved commutability with routine assays. In addition, certain SRMs, such as SRM 900 Antiepilepsy Drug Level Assay, are being updated with new analytes to better reflect current medical testing. SRM 955c Lead in Caprine Blood has been developed as a replacement for SRM 966 Toxic Elements in Bovine Blood. In addition to values for lead, this SRM will include values for inorganic and organic mercury species. New SRMs are also in development for several vitamins in serum, including vitamin B₆, B₁₂, and D. 

Many of the original reference measurement procedures for clinical analytes (formerly known as definitive methods) were based upon gas chromatography-mass spectrometry (GC/MS). These methods often required multi-step sample preparation as well as derivatization of the analyte of interest. More recently, liquid chromatography-mass spectrometry (LC/MS and LC-MS/MS) has been investigated as an alternative approach. Analyte derivatization is typically not required, and protein precipitation may be sufficient to release the analytes of interest. Both GC/MS and LC/MS methods were used to certify SRM 967 Creatinine in Human Serum, and the two techniques provided comparable results. The new LC/MS method is now listed as a higher-order method by the Joint Committee for Traceability in Laboratory Medicine (JCTLM).  

Major Accomplishments:

• NIST now has over 30 SRMs available in the area of clinical diagnostics.   
• New reference measurement procedures have been developed for analytes of clinical diagnostic significance.    
• New SRMs have been developed in consultation with the IVD industry, the clinical chemistry community, and other government agencies.