Prognostic significance of chronic myocardial injury diagnosed by three different cardiac troponin assays in patients admitted with suspected acute coronary syndrome

OBJECTIVES

Chronic myocardial injury (CMI) is defined as stable concentrations of cardiac troponin T or I (cTnT or cTnI) above the assay-specific 99th percentile upper reference limit (URL) and signals poor outcome. The clinical implications of diagnosing CMI are unclear. We aimed to assess prevalence and association of CMI with long-term prognosis using three different high-sensitivity cTn (hs-cTn) assays.

METHODS

A total of 1,292 hospitalized patients without acute myocardial injury had cTn concentrations quantified by hs-cTn assays by Roche Diagnostics, Abbott Diagnostics and Siemens Healthineers. The median follow-up time was 4.1 years. The prevalence of CMI and hazard ratios for mortality and cardiovascular (CV) events were calculated based on the URL provided by the manufacturers and compared to the prognostic accuracy when lower percentiles of cTn (97.5, 95 or 90), limit of detection or the estimated bioequivalent concentrations between assays were used as cutoff values.

RESULTS

There was no major difference in prognostic accuracy between cTnT and cTnI analyzed as continuous variables. The correlation between cTnT and cTnI was high (r=0.724-0.785), but the cTnT assay diagnosed 3.9-4.5 times more patients with having CMI based on the sex-specific URLs (TnT, n=207; TnI Abbott, n=46, TnI Siemens, n=53) and had higher clinical sensitivity and AUC at the URL.

CONCLUSIONS

The prevalence of CMI is highly assay-dependent. cTnT and cTnI have similar prognostic accuracy for mortality or CV events when measured as continuous variables. However, a CMI diagnosis according to cTnT has higher prognostic accuracy compared to a CMI diagnosis according to cTnI.

Diagnostic and prognostic value of the sex-specific 99th percentile of four high-sensitivity cardiac troponin assays in patients with suspected myocardial infarction

AIMS

High-sensitivity cardiac troponin (hs-cTn) assays are used for detection of myocardial infarction (MI). Ninety-ninth percentiles show wide inter-assay variation. The use of sex-specific cut-offs is recommended as definitory cut-off for MI. We compared diagnostic performance and prognostic value of sex-specific 99th percentiles of four hs-cTn assays in patients with suspected MI.

METHODS AND RESULTS

Concentrations of four hs-cTn assays were measured at presentation and after 3 h in patients with suspected MI. Final diagnoses were adjudicated according to the 4th Universal Definition of MI. Unisex and sex-specific 99th percentiles were evaluated as diagnostic cut-offs following the ESC 0/3 h algorithm. These cut-offs were used in Cox-regression analyses to investigate the association with a composite endpoint of MI, revascularization, cardiac rehospitalization, and death. Non-ST-elevation MI was diagnosed in 368 of 2718 patients. Applying the unisex 99th percentile, Elecsys hs-cTnT provided highest negative predictive value (NPV) of 99.7 and a positive predictive value (PPV) of 75.9. The analysed hs-cTnI assays showed slightly lower NPVs and comparable PPVs [Architect (NPV 98.0, PPV of 71.4); Atellica (NPV 97.7, PPV of 76.1); Pathfast (NPV 97.7, PPV of 66.6)]. Application of sex-specific 99th percentiles did not significantly affect diagnostic performance. Concentrations above 99th percentile were independent predictors for impaired long-term outcome (hazard ratios 1.2-1.5, P < 0.001).

CONCLUSION

We describe a good diagnostic accuracy of four hs-cTn assays using the assay-specific 99th percentile for detection of MI. Application of sex-specific 99th percentiles did neither affect diagnostic performance nor prognostic value significantly. Finally, values above the 99th percentile were associated with poor long-term outcome.

Diagnostic Role and Methods of Detection of Cardiac Troponins: An Opinion from Historical and Current Points of View

The laboratory methods for the determination of cardiac troponins (cTnI, cTnT) used nowadays are extremely diverse, which has a significant impact on our understanding of the biology and diagnostic the value of cTnI and cTnT as biomarkers. The main classification of methods for the determination of cTnI and cTnT is based on the sensitivity of the immunoassay. Low- and moderately sensitive detection methods are known to be relatively less sensitive, which leads to a relatively late confirmation of cardiomyocyte death. Due to the new highly sensitive methods used to determine cTnI and cTnT, designated as a highly or ultrasensitive immunoassays (hs-TnT and hs-TnT), we received new, revised data about the biology of cardiac troponin molecules. In particular, it became clear that they can be considered products of normal myocardium metabolism since hs-TnT and hs-TnT are detected in almost all healthy patients. It also turned out that hs-TnT and hs-TnT differ by gender (in men, troponin concentration in the blood is higher than in women), age (in elderly patients, the levels of troponins are higher than in young ones) and circadian cycles (morning concentrations of troponins are higher than in the evening). A large variety of methods for determining cTnI and cTnT, differing in their diagnostic capabilities, creates the need for tests to perform an unbiased assessment of the analytical characteristics of each method. This review focuses on the most pressing issues related to the discussion of the biological characteristics of cardiac troponin and the analytical characteristics of troponin immunoassays from a historical and contemporary point of view.

Analytical Considerations in Deriving 99th Percentile Upper Reference Limits for High-Sensitivity Cardiac Troponin Assays: Educational Recommendations from the IFCC Committee on Clinical Application of Cardiac Bio-Markers

The International Federation of Clinical Chemistry Committee on Clinical Application of Cardiac Bio-Markers provides evidence-based educational documents to facilitate uniform interpretation and utilization of cardiac biomarkers in clinical laboratories and practice. The committee's goals are to improve the understanding of certain key analytical and clinical aspects of cardiac biomarkers and how these may interplay in clinical practice. Measurement of high-sensitivity cardiac troponin (hs-cTn) assays is a cornerstone in the clinical evaluation of patients with symptoms and/or signs of acute cardiac ischemia. To define myocardial infarction, the Universal Definition of Myocardial Infarction requires patients who manifest with features suggestive of acute myocardial ischemia to have at least one cTn concentration above the sex-specific 99th percentile upper reference limit (URL) for hs-cTn assays and a dynamic pattern of cTn concentrations to fulfill the diagnostic criteria for MI. This special report provides an overview of how hs-cTn 99th percentile URLs should be established, including recommendations about prescreening and the number of individuals required in the reference cohort, how statistical analysis should be conducted, optimal preanalytical and analytical protocols, and analytical/biological interferences or confounds that can affect accurate determination of the 99th percentile URLs. This document also provides guidance and solutions to many of the issues posed.

The intra-individual variation of cardiac troponin I: the effects of sex, age, climatic season, and time between samples

OBJECTIVES

Knowing the intra-individual variation (CVi), also termed within subject biological variation, of an analyte is essential to properly interpret apparent changes in concentration. While there have been many studies assessing the CVi of cardiac troponin (cTnI), they have been limited in looking at CVi in different settings, and there is no data available on whether CVi might change in different settings.

METHODS

We used our large cTnI data bank to look at the CVi of cTnI in Emergency Department (ED) patients who had an acute myocardial infarction event excluded. We looked at the effects of gender, age, climatic season, and time between samples to assess whether CVi changed. To assess the effect of age, after exclusion, we collected two samples from each subject for each study which were used to calculate the CVi between those identified groups. There were 139 males and 98 females aged <65 years and 109 males and 98 females aged ≥65 years. For gender and season, there were 122 males and 94 females in the summer period and 126 males and 102 females in the winter period. To assess long term variation there were 195 males and 153 females who had further admissions after more than 12 months.

RESULTS

For the four variables listed, there were no significant differences in within individual variation (CVi), but there was a significant difference in between individual variation (CVg) for men and women with regard to age. The Index of Individuality (II) was <0.20 for all conditions studied. We noted that >90% of subjects had an reference change value (RCV) <9 ng/L.

CONCLUSIONS

Because troponin concentration in patients without an identified cardiac condition change so little, delta changes are potentially of great value in assessing patients in the ED. Significant delta changes in troponin can occur without the 99th percentile being exceeded.

Evaluation of the Atellica TnIH cardiac troponin I assay and assessment of biological equivalence

OBJECTIVES

We evaluated the analytical performance characteristics and the biological equivalence of the Atellica TnIH assay.

METHODS

Precision, detection capability, linearity, and sex specific 99^th percentiles were determined de novo. Classification of patients relative to the 99^th percentiles was used to assess biological equivalence.

RESULTS

Analytical precision and detection capability of the Atellica TnIH assay is excellent with a limit of blank <1 ng/L and 62.5% of women and 93% of men had results above the limit of detection. The 99th percentiles (90% CI) in women were 49 ng/L (31-67) and 70 ng/L (48-121) in men. An asymmetrical distribution involving 5% of results was notable. Agreement was moderate (Kappa 0.58, 95% CI 0.53-0.63) with 20% of patients discordantly classified with Atellica TnIH below and Access hsTnI above the 99th percentiles. Serial results in 195 patients demonstrated good agreement (Kappa 0.84, 95% CI 0.77-0.90). Differences greater than the assay specific reference change values (z_≥±1.96) occurred in 65% (95% CI 53-76%) of 99th percentile discordant patients compared to 2.7% (p<0.001) and 76% (p=0.17) of the concordant low and high cTnI groups respectively.

CONCLUSIONS

The 99th percentile discordant and the concordantly elevated groups are more alike with respect to their z_≥±1.96 rates. This favours an overestimated Atellica TnIH 99th percentile as more likely, and we hypothesize that antibody interference resulting in asymmetric scatter of nearly 5% samples may be the underlying mechanism. Analytical accuracy and interferences in cardiac troponin assays should be investigated and resolved with high priority.

Cardiac Troponins: Contemporary Biological Data and New Methods of Determination

Laboratory diagnosis plays one of the key roles in the diagnosis of many diseases, including cardiovascular diseases (CVD). The methods underlying the in vitro study of many CVD biomarkers, including cardiac troponins (cTnI and cTnT), are imperfect and are continually being improved to enhance their analytical performance, with sensitivity and specificity being the most important. Recently developed improved cTnI and cTnT detection methods, referred to as highly sensitive methods (hs-cTnI, hs-cTnT), have changed many of our ideas about the biology of cardiac troponins and opened up a number of additional diagnostic capabilities for practical healthcare. This article systematizes some relevant data on the biology of cardiac troponins as well as on methods for determining cTnI and cTnT with an analysis of the diagnostic value of their analytical characteristics (limit of blank, limit of detection, 99th percentile, coefficient of variation, and others). Data on extracardiac expression of cTnI and cTnT, mechanisms of formation and potential clinical significance of gender, age, and circadian characteristics of hs-cTnI and hs-cTnT content in serum are discussed. Considerable attention is paid to the discussion of new diagnostic capabilities of hs-cTnI, hs-cTnT, including consideration of promising possibilities for their study in biological fluids that can be obtained by non-invasive methods. Also, some possibilities of using hs-cTnI and hs-cTnT as prognostic laboratory biomarkers in healthy people (for example, to assess the risk of developing CVD) and in patients suffering from a number of pathological conditions that cause damage to cardiomyocytes are examined, and the potential mechanisms underlying the increase in hs-cTnI and hs-cTnT are discussed.

How Well Do Laboratories Adhere to Recommended Guidelines for Cardiac Biomarkers Management in Europe? The CArdiac MARker Guideline Uptake in Europe (CAMARGUE) Study of the European Federation of Laboratory Medicine Task Group on Cardiac Markers

BACKGROUND

The CARdiac MARker Guideline Uptake in Europe (CAMARGUE) program is a multi-country audit of the use of cardiac biomarkers in routine clinical practice.

METHODS

An email link to a web-based questionnaire of 30 multiple-choice questions was distributed via the professional societies in Europe.

RESULTS

374 questionnaires were returned from 39 countries, the majority of which were in northern Europe with a response rate of 8.2%-42.0%. The majority of the respondents were from hospitals with proportionately more responses from central hospitals than district hospitals. Cardiac troponin was the preferred cardiac biomarker, evenly split between cardiac troponin T (cTnT) and cardiac troponin I (cTnI). Aspartate transaminase and lactate dehydrogenase are no longer offered as cardiac biomarkers. Creatine kinase, creatine kinase MB isoenzyme, and myoglobin continue to be offered as part of the cardiac biomarker profile in approximately on 50% of respondents. There is widespread utilization of high sensitivity (hs) troponin assays. The majority of cTnT users measure hs-cTnT. 29.5% of laboratories measure cTnI by a non-hs method but there has been substantial conversion to hs-cTnI. The majority of respondents used ng/L and use the 99th percentile as the upper reference limit (71.9% of respondents). A range of diagnostic protocols are in use.

CONCLUSIONS

There is widespread utilization of hs troponin methods. A significant minority do not use the 99th percentile as recommended and there is, as yet, little uptake of very rapid diagnostic strategies. Education of laboratory professionals and clinicians remains a priority.

Evaluating the performance of an updated high-sensitivity troponin T assay with increased tolerance to biotin

OBJECTIVES

Biotin >20 ng/mL may interfere with the Elecsys^® Troponin T-high sensitive assay (cTnT-hs; Roche Diagnostics International Ltd). We evaluated the performance of an updated assay, cTnT-hs*, which was designed to reduce biotin interference.

METHODS

cTnT-hs* assay performance was assessed using up to two applications (18 min/9 min) on three analyzers (cobas e 411/cobas e 601/cobas e 801). Biotin interference was determined by measuring recovery in an 11-sample series dilution with biotin ranging from 0-3600 ng/mL. Repeatability/reproducibility were evaluated in five serum sample pools (n=75 each). Method comparisons tested: cTnT-hs* vs. cTnT-hs (18 min/cobas e 601); cTnT-hs* assay 18 vs. 9 min (cobas e 601); cTnT-hs* (18 min) on cobas e 601 vs. cobas e 411 and cobas e 601 vs. cobas e 801. Concordance at the 99th percentile decision limit between cTnT-hs* and cTnT-hs (9 min/cobas e 601) was calculated using 300 lithium-heparin plasma samples and a 14 ng/L assay cutoff.

RESULTS

cTnT-hs* assay (18 min/cobas e 601) recovery was ≥96% for biotin ≤1250 ng/mL. Across all applications/analyzers, coefficients of variation for repeatability/reproducibility with the cTnT-hs* assay were <5% in most serum sample pools (mean cardiac troponin T: 8.528-9484 ng/L). High correlation (Pearson's r=1.000) was demonstrated for all method comparisons. Concordance at the 99th percentile decision limit was high between the cTnT-hs* and cTnT-hs assays.

CONCLUSIONS

The updated cTnT-hs* assay may provide greater tolerance to biotin interference, and shows good analytical and clinical agreement/concordance with the previous cTnT-hs assay.

Determination of high sensitive cardiac troponin I 99th percentile upper reference limits in a healthy Pakistani population

OBJECTIVE

This study aims to establish the 99^th percentile upper reference limits of high sensitive cardiac troponin I in a healthy Pakistani population.

METHODS

It was an Observational cohort study carried out in Department of Chemical Pathology and Endocrinology Rehman Medical Institute Peshawar, over the period of one year (January 2019- December 2019). Total 299 cardio-healthy males and females were interviewed and taken past medical history. Based on history, clinical examination, echocardiogram and laboratory data including results of estimated glomerular filtration rate (eGFR) and N-terminal pro-B-type natriureteric peptide (NT-proBNP), subjects with possible subclinical diseases were excluded. High Sensitive Cardiac Troponin I (hs-cTtrop I) was analysed on Abbot ARCHITECT STAT ci8200 using chemiluminescent immunoassay technique. The 99th percentile upper reference limit (URL) of hs-cTtrop I was determined using a non-parametric statistic, while gender specific results were compared.

RESULTS

In this study, 178 males (59.5%) and 121 females (40.5%) were included. The median Interquartile ranges (IQR) of age was 57 (11.6) for males and 56 (13) for females. The 99th percentile URL hs-cTtrop I was found to be 33.9 ng/L, while gender specific values were 38.41ng/L and 15.73ng/L for males and females, respectively (p= 0.0045).

CONCLUSION

High sensitivity cardiac troponin I 99th percentile URL in our study population was found to be 33.9 ng/L with gender specific values being 38.41 ng/L and 15.73ng/L for males and females respectively. Troponin I in males was substantially high in comparison with females.

Establishing the 99th percentile of a novel assay for high-sensitivity troponin I in a healthy blood donor population

Background

The recommended cut-off of cardiac troponin (cTn) for the diagnosis of acute myocardial infarction (AMI) is the 99th percentile in a healthy reference population. We aimed to determine the 99th percentile of the novel ADVIA Centaur® High Sensitivity Troponin I assay (Siemens Healthcare Diagnostics) in fresh lithium heparin plasma samples from healthy blood donors.

Methods

A total of 1000 apparently healthy blood donors were included. High-sensitivity (hs) cTnI, hs-cTnT, creatinine and N-terminal pro b-type natriuretic peptide (NT-proBNP) were measured in fresh lithium heparin plasma samples, and glycated hemoglobin (HbA1c) was measured in ethylenediaminetetraacetic acid (EDTA)-blood. The 99th percentile was estimated for the whole population, as well as for males and females separately.

Results

For the total population the 99th percentile of ADVIA Centaur® High Sensitivity Troponin I was 96 (65-149) ng/L. The estimated value differed significantly from results published by others and was highly dependent on which values were considered statistical outliers.

Conclusions

The estimated 99th percentile for hs-cTnI in the population studied differed significantly from previously published results. There is a need for further specifications regarding how subjects used for estimating the 99th percentile of cTns in healthy populations should be recruited and how outlier values should be identified, as this can highly influence the diagnostic cut-off applied for AMI.

Optimal Detection of Acute Myocardial Injury and Infarction with Cardiac Troponin: Beyond the 99th Percentile, into the High-Sensitivity Era

PURPOSE OF REVIEW

Cardiac troponin (cTn) is the biomarker of choice for the diagnosis of acute myocardial infarction (MI); use of this biomarker has centered around the 99th percentile upper reference limit (URL) for healthy populations. Recent development and regulatory approval of high-sensitivity cardiac troponin (hs-cTn) assays have required a fresh look at utilization of the 99th percentile URL. This review covers issues regarding the 99th percentile URL and approaches for use of cTn as biomarker for detecting cardiac injury and diagnosis of acute myocardial infarction.

RECENT FINDINGS

Development of hs-cTn assays has allowed determination and use of sex-specific 99th percentile URLs for assessing cardiac injury and increased the utility of cTn values below the 99th percentile URL. This improved analytical performance for hs-cTn assays has allowed for development of accelerated diagnostic protocols (ADPs) for rapid assessment and disposition of patients based on serial sampling of cTn for use in acute MI diagnosis as soon as 0-1 h after clinical presentation. The 99th percentile URLs of cTn is essential for detecting cardiac injury; however, use of the 99th percentile URLs in the era of hs-cTn results may be modified. ADPs have the potential to substantially decrease the time many patients spend under evaluation for acute MI, thereby potentiating improvement in patient satisfaction, decreased healthcare costs, and reducing the burden on emergency departments.

The 99th percentile upper reference limit for the 5th generation cardiac troponin T assay in the United States

BACKGROUND

Determining diagnostic thresholds for cardiac troponin assays is key to interpreting their clinical performance. We describe the calculation of 99th percentile upper reference limits (URLs) for the Elecsys® Troponin T Gen 5 (TnT Gen 5) assay.

METHODS

Plasma and serum samples from healthy US participants were prospectively evaluated using TnT Gen 5 Short Turn Around Time and 18-min assays on cobas e 411 and cobas e 601 analyzers (Roche Diagnostics); with, up to 8 TnT Gen 5 results per participant.

RESULTS

A total of 10,402 TnT Gen 5 results from 1301 participants were included (50.4% female). Across 9 calculation methods, overall 99th percentile URL was 19.2 ng/l (females, 13.5-13.6 ng/l; males, 21.4-22.2 ng/l). Across different sample/assay/analyzer combinations, overall 99th percentile URLs ranged from 18.4-20.2 ng/l. Median TnT Gen 5 results increased with age, were higher in males, and ranged from 3.0-3.7 ng/l across races/ethnicities and from 3.0-3.6 ng/l across body mass index (BMI) classes. Applying additional exclusion criteria (N-terminal pro-brain natriuretic peptide, BMI and estimated glomerular filtration rate) resulted in lower 99th percentile URLs (overall, 16.9 ng/l; females, 11.8 ng/l; males, 18.5 ng/l).

CONCLUSION

Our findings facilitate the interpretation of TnT Gen 5 results in US clinical practice.

Establishing the 99th percentile for high sensitivity cardiac troponin I in healthy blood donors from Southern Italy

Introduction

The knowledge of high sensitivity cardiac troponin I (hsTnI) distribution in a reference population is mandatory for its introduction in clinical practice. The aim of this study was to define the Upper Reference Limit (URL) of hsTnI measured by Single Molecule Counting technology (SMC) in an accurately selected reference population.

Materials and methods

In the study 1140 blood donors were included and selected on the basis of medical history and biomarkers. High sensitivity cardiac troponin I was measured by SMC technology (Clarity, Singulex, Alamed, USA). The 99th percentile was calculated by the non-parametric method according to the Clinical and Laboratory Standard Institute - CLSI C28-A3.

Results

The median age was 41 years (IQR: 28 - 50) and 69% were males. The overall 99th percentile was 5 ng/L (90% CI: 4.2 - 5.6). When considering sex-related differences, we found slight differences between the 99th percentile in males and females. Moreover, the 99th percentile trended with age, especially in females.

Conclusions

We defined the 99th percentile of hs-cTnI measured by SMC technology in a highly selected healthy population, with only minor differences between males and females. Our findings provide the basic criteria for the reliable interpretation of hsTnI concentrations measured by the SMC technology in clinical settings.

Determination of high-sensitivity cardiac troponin T upper reference limits under the improved selection criteria in a Chinese population

BACKGROUND

There is no common consensus on how to define the reference population for determination of high-sensitivity cardiac troponin (hs-cTn) upper reference limit (URL). This study aimed to establish 99th percentile URLs of hs-cTnT under both 2018 AACC/IFCC criteria and improved selection criteria for further judging whether two URLs are different.

METHODS

Applying the stratified cluster sampling protocol, this study took 1848 apparently healthy subjects in communities of Shenyang China as the screening objects. We first followed 2018 AACC/IFCC criteria using surrogate biomarker for diabetes, myocardial dysfunction, renal dysfunction, and electrocardiogram. Then, we followed improved selection criteria to exclude hypertension, overweight and obesity, and dyslipidemia by physical examination and laboratory screening. Accordingly, 99th percentile URLs of hs-cTnT were established.

RESULTS

If the 2018 AACC/IFCC criteria were applied, 99th percentile URLs (90% confidence interval) of hs-cTnT male, female, and total were 19 (17-20) ng/L, 16 (15-17) ng/L, and 18 (16-19) ng/L, respectively. If added a single supplementary selection criteria, 99th percentile URLs of hs-cTnT total reduced to 16 ng/L, 17 ng/L, and 16 ng/L, respectively. If the improved selection criteria were applied, 99th percentile URLs (90% confidence interval) of hs-cTnT male, female, and total were 18 (14-24) ng/L, 13 (11-16) ng/L, and 16 (13-17) ng/L, respectively. The 99th percentile URLs of hs-cTnT male were higher than those of female in every age group.

CONCLUSIONS

Improved selection criteria through questionnaire survey, physical examination, and laboratory screening to further exclude hypertension, overweight and obesity, and dyslipidemia can avoid overestimation of the 99th percentile URL of hs-cTnT.

Trial design for assessing analytical and clinical performance of high-sensitivity cardiac troponin I assays in the United States: The HIGH-US study

BACKGROUND

High-sensitivity cardiac troponin I (hs-cTnI) assays have been developed that quantify lower cTnI concentrations with better precision versus earlier generation assays. hs-cTnI assays allow improved clinical utility for diagnosis and risk stratification in patients presenting to the emergency department with suspected acute myocardial infarction. We describe the High-Sensitivity Cardiac Troponin I Assays in the United States (HIGH-US) study design used to conduct studies for characterizing the analytical and clinical performance of hs-cTnI assays, as required by the US Food and Drug Administration for a 510(k) clearance application. This study was non-interventional and therefore it was not registered at clinicaltrials.gov.

METHODS

We conducted analytic studies utilizing Clinical and Laboratory Standards Institute guidance that included limit of blank, limit of detection, limit of quantitation, linearity, within-run and between run imprecision and reproducibility as well as potential interferences and high dose hook effect. A sample set collected from healthy females and males was used to determine the overall and sex-specific cTnI 99th percentile upper reference limits (URL). The total coefficient of variation at the female 99th percentile URL and a universally available American Association for Clinical Chemistry sample set (AACC Universal Sample Bank) from healthy females and males was used to examine high-sensitivity (hs) performance of the cTnI assays. Clinical diagnosis of enrolled subjects was adjudicated by expert cardiologists and emergency medicine physicians. Assessment of temporal diagnostic accuracy including sensitivity, specificity, positive predictive value, and negative predictive value were determined at presentation and collection times thereafter. The prognostic performance at one-year after presentation to the emergency department was also performed. This design is appropriate to describe analytical characterization and clinical performance, and allows for acute myocardial infarction diagnosis and risk assessment.

Assessment of Access hsTnI 99th percentiles upper reference limits following IFCC recommendations

BACKGROUND

The detection of an increase and/or decrease of cardiac troponin (cTnI) values, with at least one value above the 99th percentile of the upper reference limit (URL) have a central role in acute myocardial infarction (AMI) diagnosis. The employment of sex specific 99th percentile URLs and High-sensitivity (Hs) assays are recommended. We assessed sex specific 99th percentile URL for Access Hs-cTnI and AccuTnI3+ (Beckman Coulter) using European donor reference population following recent International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) recommendations.

METHODS

300 males and 300 females plasma samples were collected. Both chemiluminescent immunoenzymatic assays were performed on UniCel DxI 800 platform (Beckman Coulter).

RESULTS

For Access hsTnI, the observed sex-specific 99th percentile URLs were 5.5 (90% CI: 4.4-7.6) for females and 13.9 ng/L (90% CI: 7.4-17.4) for males. For AccuTnI+3 we could not establish them because the assay couldn't report detectable values of troponin for most of the analyzed samples.

CONCLUSION

The sex-specific 99th percentile URLs established for Access hsTnI assay were significantly lower than those declared by the manufacturer caused by the different choice of population selection, age groups and sample types: for those reasons, we maintain the 99th URLs provided by manufacturer.

Validation of high-sensitivity performance for a United States Food and Drug Administration cleared cardiac troponin I assay

BACKGROUND

High-Sensitivity (hs) cardiac troponin (cTn) assays are categorized by two criteria: (i) cTn values above the limit of detection (LoD) for >50% of male and female healthy cohorts of ≥300 individuals; (ii) imprecision ≤10% total %CV for sex-specific 99th-percentile clinical decision values (CDVs). No documented hs-Tn assay has yet been FDA-cleared.

METHODS

The PATHFAST cTnI-II assay's LoD was 2.3 ng/L using CLSI EP-17. The AACC Universal Sample Bank of 847 healthy men (50.6%) and women (49.4%) was used to determine 99th-percentile CDVs with Nonparametric, Harrell-Davis and Robust modeling. Health/Medication questionnaires and Amino-terminal proBNP, Hemoglobin A_1c and estimated Glomerular Filtration Rate surrogates excluded underlying health conditions.

RESULTS

The cTnI-II test's total CV was 6.1% at 29 ng/L and 7.1% at 22 ng/L; the LoD was 2.3 ng/L. Of the full 847-member healthy cohort, 113 (13.3%) were excluded by abnormal surrogate biomarkers. The final 734-member healthy population had the following (% > LoD): overall, 487 (66.3%); women, 186 (52.8%); and men, 301 (78.8%). 99th-percentile CDVs by Nonparametric modeling were: 28 ng/L (90% CI: 20-30), overall final 732-member healthy population; 20 ng/L (90% CI: 13-30), 352 women; and 30 ng/L (90% CI: 21-37), 382 men. Differences between sex-specific CDVs were not significantly different (p > .05) with Nonparametric or Harrell-Davis modeling; however, Robust Modeling did show significance (<0.05), with lower CDVs at 11 ng/L (90% CI: 9-12) and 16 ng/L (90% CI: 15-18) for the female and male cohorts, respectively.

CONCLUSIONS

cTnI-II is the only FDA-cleared assay that has demonstrated high-sensitivity cTn assay. Use of recommended modeling in >300 healthy subjects for determining sex-specific 99th-percentile CDVs did not show statistically significant differences except with the Robust modeling.

Distribution of cardiac troponin I in the Japanese general population and factors influencing its concentrations

BACKGROUND

The 99th percentile of cardiac troponin I level in the general population is accepted as the cut-off for the diagnosis of acute myocardial infarction (AMI). However, it is not clear whether the cut-offs derived in racially and geographically different populations are applicable in Japan.

METHODS

Troponin I was determined using the Abbott ARCHITECT STAT high-sensitive troponin I immunoassay in 698 apparently healthy individuals who visited the Japanese Red Cross Medical Center for a health checkup.

RESULTS

The 99th percentile of the hsTnI in the overall population was 22.5 (95% confidence interval (CI), 16.8-36.6) pg/mL, 17.7 (95% CI 12.0-22.8) pg/mL for females and 30.6 (95% CI 17.1-53.4) pg/mL for males. The median of the hsTnI in the overall population was 3.2 (95% CI, 3.0-3.3) pg/mL, 2.6 (95% CI 2.4-2.8) pg/mL for females and 4.0 (95% CI 3.8-4.3) pg/mL for males. The age and gender had a significant influence on these values. The troponin I level also showed significant associations with the body mass index (BMI), the gamma glutamyl transferase (GGT), lactate dehydrogenase (LDH), estimated glomerular filtration rate (eGFR), and cardiac abnormalities by electrocardiography (ECG) but not with the high-sensitive C-reactive protein (hsCRP) level.

CONCLUSIONS

The 99th percentiles of the troponin I measured in the general population in Japan were comparable as the ones derived in the US, Germany, and Singapore. The troponin I level was dependent on the gender, age, BMI, and cardiac abnormalities found by ECG but not by the hsCRP level.

Laboratory diagnosis of gestational diabetes: An in silico investigation into the effects of pre-analytical processing on the diagnostic sensitivity and specificity of the oral glucose tolerance test

INTRODUCTION

Delayed separation of red cells from plasma causes pre analytical glucose loss, which in turn results in an under-diagnosis of GDM (gestational diabetes) based on the OGTT (oral glucose tolerance test). In silico investigations may help laboratory decision making, when exploring pragmatic improvements to sample processing.

METHODS

Late pregnancy 0, 1 and 2h 75g OGTT values were obtained from two distinct populations of pregnant women: 1. Values derived from the HAPO (Hyperglycemia and Adverse Pregnancy Outcome) Study and 2. New Zealand women identified as at higher risk of GDM by their caregivers, undergoing OGTT during routine antenatal care. In both populations studied, in silico modelling focussed on the effects of pre-analytical delays in plasma separation, when using fluoride collection tubes.

RESULTS

Using a model that 'batched' samples from the three OGTT collection times, diagnostic sensitivity was estimated as follows: 66.1% for HAPO research population and 48.4% for the 1305 women receiving routine antenatal care. If samples were not batched, but processed shortly after each blood sample was collected, then sensitivity increased to 81%.

CONCLUSION

Exploration of a range of clinical and laboratory scenarios using in silico modelling, showed that delaying the processing of pregnancy OGTT samples, using batched sample collection into fluoride tubes, causes unacceptable loss of GDM diagnostic sensitivity across two distinct population groups. This modelling approach will hopefully provide information that helps with final decision making around improved laboratory processing techniques.

Challenging the 99th percentile: A lower troponin cutoff leads to low mortality of chest pain patients

BACKGROUND

Rule-out of non-ST-elevation myocardial infarction is based on consecutive measurements of cardiac troponins using the 99th percentile of the respective assay as cutoff. The new ESC guidelines alternatively offer rapid 1h algorithms with lower cutoffs than the 99th percentile for rule-out of non-ST-elevation myocardial infarction. We aimed to compare a recently introduced 1h algorithm based on a high-sensitivity cardiac troponin I (hs-TnI) cutoff of 6ng/L at 0h and 1h to the current standard of care using the 99th percentile (27ng/L) as cutoff with reference to follow-up events in a large chest pain cohort.

METHODS

Hs-TnI was measured at three time points (0h, 1h and 3h) in 1625 patients presenting with suspected myocardial infarction to the emergency department of the University-Medical Center Hamburg-Eppendorf. Seventy-five patients with ST-elevation myocardial infarction were excluded from the analysis. All-cause mortality, cardiac death, acute myocardial infarction, revascularization and cardiac rehospitalization after 12months were assessed.

RESULTS

Patients ruled out by the 1h algorithm showed significantly less cardiac rehospitalizations (12.84% vs. 17.66%; p<0.001), and overall mortality (1.30% vs 3.46%, p<0.001) compared to using the 99th percentile as cutoff. The majority of deaths were caused by non-cardiac reasons. Cardiac deaths were rare using the 1h algorithm (0.21%).

CONCLUSION

The commonly used 99th percentile as cutoff neglects patients with a high risk in the setting of acute chest pain.

TRIAL REGISTRATION

www.clinicaltrials.gov (NCT02355457).

Impact of physical activity of individuals and creatine kinase on 99th percentiles of troponin I assays

Determination of cardiac troponin I (cTnI) is one central means for diagnosis of myocardial infarction. Assay performance of three troponin I assays was compared previously in a large reference population detecting sex-differences in the 99th percentile only for the Dimension Vista cTnI assay. The present study examined the underlying effects. Values for cTnI were reused. Creatine kinase (CK) activity was determined in 2358 samples from blood donors. Information on physical activity was evaluated from health questionnaires. Using quantile regression data were analysed to investigate the impact of sex, physical activity, and CK on the 99th percentile of the cTnI assay. We report significant sex-differences for the 99th percentile of cTnI. Physical activity was significantly associated with cTnI values. Strong association of CK activity with cTnI values was detected only in men. Adjustment for CK in quantile regression abolished sex-differences in the 99th percentile. Two other contemporary sensitive cTnI assays were not relevantly affected by physical activity or CK. Sex-differences in the 99th percentile for the Dimension Vista cTnI assay arise from a positive association between cTnI and physical activity and were abrogated when data were adjusted for CK activity. These findings should be taken into account when using this assay.

Determination of high-sensitivity cardiac troponin I 99th percentile upper reference limits in a healthy Korean population

OBJECTIVES

This study aimed to determine the 99th percentile upper reference limit (URL) concentration of cardiac troponin I (cTnI) with a high-sensitivity assay in a Korean population.

DESIGN AND METHODS

Cardio-healthy males and females were enrolled between March 2014 and March 2015. Participants with possible subclinical conditions were excluded on the basis of laboratory measures (primary: estimated glomerular filtration rate and glycated hemoglobin; secondary: B-type natriuretic peptide). Serum cTnI was measured using ARCHITECT STAT High-Sensitive Troponin-I Assay (Abbott Diagnostics, USA).

RESULTS

A total of 1204 participants completed a self-reporting questionnaire for inclusion in the study. Of these, we excluded 349 (29.0%) participants on the basis of primary (n=283) and secondary (n=66) laboratory measures. Ultimately, we included 854 participants (mean age, 49.8±10.2years) in the final analysis. The 99th percentiles of cTnI concentrations were 18 (90% confidence interval [CI], 14-35) ng/L for all participants, 20 (90% CI, 15-69) ng/L for males and 19 (90% CI, 11-41) ng/L for females. In both males and females, the median cTnI concentrations were significantly higher in participants aged 50years and older than in those younger than 50years old.

CONCLUSIONS

In this study, the reference population with Korean ethnicity had lower overall and male 99th percentile URLs than other reference populations. Our data suggest that 99th percentile URLs may be influenced by factors such as ethnicity, age distribution of participants, and selection criteria used to define a healthy reference population.

The distribution of Abbott high-sensitivity troponin I levels in Korean patients with chest pain

BACKGROUND

Troponin is considered a primary biomarker for coronary heart disease. We investigated the clinical utility of the Abbott high-sensitivity cardiac troponin I (hs-TnI) assay in patients with various cardiac problems.

METHODS

Precision was investigated by ten levels of pooled sera and three levels of control materials. We determined Abbott hs-TnI levels in a total of 3314 Korean patients with chest pain, including acute myocardial infarction (n=381), unstable angina (n=327), stable angina (n=1361), variant angina (n=189), non-coronary artery diseases (n=236), and nonspecific chest pain (n=820). The 99(th) percentile cutoff was established by the plasma from the cardio-healthy subgroup and validated by 118 healthy individuals.

RESULTS

The total coefficient of variation in patient pooled sera and controls ranged from 3.93-6.35% and 4.81-9.73%, respectively. There was a significant difference in hs-TnI among various cardiac problems: subjects with non-cardiac chest pain (median 1.7 pg/mL, 25%/75% quartile 1.1/2.8 pg/mL), variant angina (2.4 pg/mL,1.4/5.6 pg/mL), stable angina (3.7 pg/mL, 2.1/8.9 pg/mL), unstable angina (10.7 pg/mL, 3.7/61.7 pg/mL), and non-coronary artery diseases (9.3 pg/mL, 4.3/37.4 pg/mL). However, the median levels of hs-TnI were not statistically different (p=0.921) between unstable angina and non-coronary artery diseases. The overall 99(th) percentile cutoff was 19.3 pg/mL (range 0.2-30.6 pg/mL).

CONCLUSIONS

This new hs-TnI assay may be helpful in determining a differential diagnosis in patients with chest pain.

Effect of population selection on 99th percentile values for a high sensitivity cardiac troponin I and T assays

OBJECTIVE

Using objective laboratory and clinical criteria to more accurately determine the 99th percentile values for cardiac troponin I and T.

DESIGN AND METHODS

We measured cardiac troponin T and cardiac troponin I with high-sensitivity assays in a large cohort of apparently healthy community subjects and calculated 99th percentiles for different sexes and ages. Subjects with possible subclinical disease were eliminated based on objective laboratory criteria, eGFR and NT-proBNP, and clinical criteria, history and examination and echocardiogram.

RESULTS

For men and women of all ages, separately, more than 50% of subjects were excluded using these criteria, with a lesser proportion of younger subjects being excluded. In men aged <75 years, the 99th percentile for cTnI decreased by more than 50% from 22.9 ng/L to 10.3 ng/L. In other age groups and for cTnT the decrease was smaller (%) but still considerable.

CONCLUSIONS

For establishing cardiac troponin 99th percentiles, simply using self-reporting of health is insufficient. Objective laboratory measures and clinical and echocardiographic assessments are essential to define a healthy population, especially in older persons.