The 99th percentile of reference population for cTnI and cTnT assay: methodology, pathophysiology and clinical implications

Abstract

According to recent international guidelines, including the 2012 Third Universal Definiton of Myocardial Infarction by the Joint ESC/ACCF/AHA/WHF Task Force, an increase in cardiac troponin (cTn) levels over the 99th percentile upper reference limit (99th URL) should be considered clinically relevant, this cut-off being measured with an imprecision ≤10 CV%. In theory 99th URL values strongly depend not only on demographic and physiological variables (i.e. criteria for considering the reference population "healthy"), but also on the analytical performance of cTn methods and mathematical algorithms used for the calculation. The aim of the present article was therefore to review the methodological and pathophysiological factors affecting the evaluation and calculation of the 99th URL for cTn assay. The critical analysis made showed that no uniform procedure is followed, and nor have experts or regulatory bodies provided uniform guidelines for researchers or cTn assays manufacturers as an aid in "their quest to define normality". In particular, little attention has been paid to the way in which a healthy reference population is to be selected, or the criteria for calculating the 99th URL value for cTn assays, thus highlighting the need for international recommendations not only for demographic and physiological variables criteria for defining a healthy reference population, but also for calculating mathematical algorithms for establishing/ calculating clinical decision values. An expert consensus group, comprising laboratory and clinical scientists, biomedical statisticians, industrial and regulatory representatives, should be responsible for drawing up these guidelines.

ANMCO/ELAS/SIBioC Consensus Document: biomarkers in heart failure

“…First, it is important to accurately define the analytical specifications characterizing the highly sensitive methods 66 , 67 . One should define methods with high sensitivity only the immunoassays that measure the 99th percentile of the distribution of proteins cTnI and cTnT in the reference population (99th ULN) with an error (expressed as coefficient of variation, CV) equal to or lower than 10%, 66 , 67 as required by all the most international guidelines, including the Third Universal Definition of Myocardial Infarction 6 . The methods showing an intermediate imprecision (10–20%) should be considered clinically usable (but not highly sensitive methods) 6–8 , 66 , 67 .…”

“…One should define methods with high sensitivity only the immunoassays that measure the 99th percentile of the distribution of proteins cTnI and cTnT in the reference population (99th ULN) with an error (expressed as coefficient of variation, CV) equal to or lower than 10%, 66 , 67 as required by all the most international guidelines, including the Third Universal Definition of Myocardial Infarction 6 . The methods showing an intermediate imprecision (10–20%) should be considered clinically usable (but not highly sensitive methods) 6–8 , 66 , 67 . The reference population on which the 99th URL value is calculated should consist of at least 300 apparently healthy subjects of both genders with a broad age distribution (usually from 18 to 70 years) 7 , 66 , 67 .…”

High-sensitivity assays for cardiac troponins – continued

“…The articles covered a broad spectrum of critical topics which were debated in the scientific community and they addressed gaps of knowledge associated with the use of these novel assays. In this issue we have again a series of articles dealing with various aspects of the novel assays for cTn showing clearly that even though there has been substantial progress there are still unanswered questions and unmet needs in the field [2][3][4][5][6][7].…”

“…This immediately raises the question, whether we should spend much effort on determination of the 99th percentile or rather on clinical studies providing individual NPV and PPV. As Clerico et al [4] discuss in detail, determination of the 99th percentile is strongly dependent on the selection of the reference cohort. Age, sex, underlying cardiac and non-cardiac diseases all affect individual cTn concentrations.…”

“…While there is ample evidence that women have lower cTn plasma concentrations than men and the 99th percentiles of the sexes are significantly different, the use of sex specific cutoffs is not uniform [4]. Interestingly, most rapid rule-out and rule-in strategies proposed so far do not take this sex difference into account [8][9][10][11][12].…”