Characterization of a New Certified Reference Material for Human Cardiac Troponin I

BACKGROUND: To address the continuing need for the standardization of clinical human cardiac troponin I (cTnI) assays, NIST, with the assistance of the AACC/IFCC Cardiac Troponin I Standardization Committee, has developed a new certified reference material, Standard Reference Material (SRM) 2921: Human Cardiac Troponin Complex. METHODS: The concentration of cTnI in SRM 2921 was determined through a combination of reversed-phase liquid chromatography (LC) with ultraviolet detection and amino acid analysis. Characterization of the intact troponin subunits was accomplished through reversed-phase LC coupled with mass spectrometry. Posttranslational modifications to the cTnI in SRM 2921 were investigated by combining proteolytic digestion with matrix-assisted laser desorption/ionization mass spectrometry. Additionally, reference concentration values for cTnT and cTnC were also determined. RESULTS: The concentration of human cTnI in SRM 2921 is 31.2 (1.4) mg/L (where 1.4 mg/L is the uncertainty at a 95% level of confidence), as certified through a method that provides traceability to the International System of Units (SI). Reference concentration values of the cTnT and cTnC subunits were determined to be 36.9 (3.8) mg/L and 24.2 (1.3) mg/L, respectively. CONCLUSIONS: This first cTnI reference material should provide SI traceability to clinical cTnI assays once commutability has been validated, and could assist in the international harmonization of cTnI assays as a tool for understanding the underlying causes of interassay variability.