National Academy of Clinical Biochemistry and IFCC Committee for Standardization of Markers of Cardiac Damage Laboratory Medicine Practice Guidelines: Analytical Issues for Biochemical Markers of Acute Coronary Syndromes

Abstract

I. OVERVIEW OF ANALYTICAL ISSUES FOR ACUTE CORONARY SYNDROME (ACS) BIOMARKERS…548 A. Analytical Issues: Background…548 II. ANALYTICAL BIOMARKER ISSUES…548 A. Cardiac Troponin Specifications…548 B. Cardiac Biomarker Turnaround…549 C. Biomarkers No Longer Recommended for Use in the Context of ACS…549 D. Determining Biomarker Decision Cutoff Characteristics for ACS…549 E. European Society of Cardiology (ESC)/American College of Cardiology (ACC) Recommendations…550 III. REFERENCES…550 In 1999, the National Academy of Clinical Biochemistry (NACB)1 published the first standards of laboratory practice addressing analytical and clinical recommendations for use of cardiac markers in coronary artery diseases (1). The objectives were to recommend the appropriate implementation and utilization of cardiac biomarkers, specifically for cardiac troponin (cTn), which had just gained US Food and Drug Administration (FDA) clearance as a cardiac biomarker to aid in the diagnosis of acute myocardial infarction (AMI). In 2001, the IFCC Committee on Standardization of Markers of Cardiac Damage (C-SMCD) recommended quality specifications for analytical and preanalytical factors for cTn assays (2). The objectives were intended for use by the manufacturers of commercial assays and by clinical laboratories that use cTn assays. The overall goal was to establish uniform criteria so that all cTn assays could objectively be evaluated for their analytical qualities and clinical performance. These general principles can also be applied to creatine kinase MB (CK-MB) mass and myoglobin assays by use of the analytical recommendations in this document. In this report, we provide the background for establishing updated practice guidelines with recommendations addressing analytical issues for cardiac biomarkers based on 8 years of evidence-based medical and scientific observations since the publication of the initial recommendations (1). ALL CLASS I Reference decision-limits should be established for each cardiac biomarker based on a population of normal, healthy individuals without a known history of heart disease (reference population). For cardiac troponin I (cTnI) and T (cTnT), as well as for CK-MB mass, the 99th percentile of the reference population should be the decision-limit for myocardial injury. The Clinical Laboratory Standards Institute (CLSI; formerly NCCLS) recommends a minimum of 120 individuals per group of healthy individuals for appropriate statistical determination of a normal reference limit cutoff. Sex-specific reference limits should be used in clinical practice for CK-MB mass. For myoglobin, the 97.5th percentile (with sex-specific reference limits) should be the decision-limit for myocardial injury (Level of Evidence: B). One decision-limit, the 99th percentile, is recommended as the optimum cutoff for cTnI, cTnT, and CK-MB mass. ACS patients with cTnI and cTnT results above the decision-limit should be labeled as having myocardial injury and a high-risk profile (Level of Evidence: B). Assays for cardiac biomarkers should strive for a total imprecision (%CV) of ≤10% at the 99th percentile reference limit. Before introduction into clinical practice, cardiac biomarker assays must be characterized with respect to potential interferences, including rheumatoid factors, human anti-mouse antibodies, and heterophile antibodies. Preanalytical and analytical assay characteristics should include biomarker stability (over time and across temperature ranges) for each acceptable specimen type used in clinical practice and identification of antibody/epitope recognition sites for each biomarker. Analytical and preanalytical specifications developed by professional groups such as the IFCC should be followed (Level of Evidence: C). Serum, plasma, and anticoagulated whole blood are acceptable specimens for the analysis of cardiac biomarkers. Choice of specimen must be based on sufficient evidence and the known characteristics of individual biomarker assays (Level of Evidence: C). First, in the context of cTn, the epitopes recognized by the antibodies must be delineated. Epitopes located on the stable part of the cTnI molecule should be a priority. Specific relative responses need to be described for the following cTnI forms: free cTnI, the I-C binary complex, the T-I-C ternary complex, and oxidized, reduced, and phosphorylated isoforms of the 3 cTnI forms. The effects of different anticoagulants on binding of cTnI also need to be addressed. Second, the source of material used to calibrate cTn assays, specifically for cTnI, should be reported. A cTnI standardization subcommittee of the AACC in collaboration with the NIST has developed a primary reference material (SRM #2921) (3). Although this material demonstrated commutability with only 50% of current cTn assays, it will be of use in harmonizing cTnI concentrations across different assays (4)(5). At present, it appears that the only way to achieve complete standardization for cTnI would b