Clinical and analytical performance of the liaison cardiac troponin I assay in unstable coronary artery disease, and the impact of age on the definition of reference limits. A FRISC-II substudy

Cardiac troponin I in healthy Norwegian Forest Cat, Birman and domestic shorthair cats, and in cats with hypertrophic cardiomyopathy

Objectives

The aims of this study were to assess the potential associations between the serum cardiac troponin I (cTnI) concentration in healthy cats and feline characteristics, systolic blood pressure, heart rate (HR), echocardiographic measurements and storage time; and to compare cTnI concentrations in healthy cats with concentrations in cats with hypertrophic cardiomyopathy (HCM), with or without left atrial enlargement (LAE) and in cats with HCM, to assess potential associations between cTnI concentration and echocardiographic variables.

Methods

Cardiac TnI was analysed using an Abbott ARCHITECT ci16200 analyser in serum from prospectively included healthy Norwegian Forest Cat (NF; n = 33), Birman (n = 33) and domestic shorthair (DSH; n = 30) cats, and from 39 cats with HCM, with or without LAE.

Results

In healthy cats, higher cTnI concentrations were found in Birman cats than in NF cats (P = 0.014) and in neutered male cats than in intact females (P = 0.032). Cardiac TnI was positively associated with HR (P <0.0001). In cats with HCM, cTnI concentration was positively associated with left ventricular wall thickness and with left atrial-to-aortic root ratio (all P ⩽0.010). Cats with HCM had higher cTnI concentrations than healthy cats, and cTnI concentrations were higher in cats with HCM and LAE than in those with HCM without LAE (all P = 0.0003).

Conclusions and relevance

Breed and sex may affect serum cTnI concentrations in healthy cats. The cTnI concentration increased with increasing severity of HCM.

Retrospective cause analysis of troponin I elevation in non-CAD patients: Special emphasis on sepsis

BACKGROUND

Troponin I is one of the most commonly tested biochemical markers in the emergency room (ER) and in the hospital setting. Besides coronary artery disease (CAD), demand ischemia with underlying tachycardia, anemia, hypertensive emergency, congestive heart failure, kidney disease, sepsis, and pulmonary embolism have also been reported to cause troponin I elevations. Few reports have excluded patients with CAD, and no study has summarized the proportion of these factors relative to an increased troponin I level.

METHODS

The aim of this retrospective study was to investigate the level of contribution of causative factors in troponin I elevation. Charts of patients tested for troponin I during an ER visit or during hospitalization were collected. Patients with known CAD, abnormal stress tests, cardiac catheterizations, or discharge without an adequate cardiac evaluation were excluded. Logistic regression was used to identify predictors of elevated troponin I levels.

RESULTS

A total of 586 patients were investigated in this study. Age, hemoglobin (Hb), heart rate (HR), glomerularfiltration rate, atrial fibrillation, congestive heart failure (CHF), and sepsis were significant predictors of elevated troponin I by analysis in univariate logistic regression (all P < .001). In multivariate logistic regression, sepsis, CHF, age, Hb, and HR were independent predictors of troponin I (all P < .01). A simple clinical scoring system was generated with 1 score on patients with age ≥ 60, Hb < 10 g/dL, and HR ≥ 100 beats per minute (bpm). The prevalence of elevated troponin I was 4%, 16%, 38%, and 50% for patients with scores of 0, 1, 2, and 3, respectively. In patients without sepsis and CHF, the chances of elevated troponin I were 2%, 11%, 28%, and 43%.

CONCLUSIONS

Sepsis was found to be the strongest independent cause of elevated troponin I levels in non-CAD patients. The scoring system composed of age, hemoglobin (Hb), and heart rate (HR) can assist clinical evaluation of elevated troponin I test in non-CAD patients.

Decision limits and the reporting of cardiac troponin: Meeting the needs of both the cardiologist and the ED physician

Cardiac troponin is the preferred biomarker for defining the acute coronary syndrome and acute myocardial infarction. Currently, the only decision limit formally endorsed with regard to the cardiac troponins is the 99th percentile. This is a "rule-in" criterion, intended to ensure that only persons with the acute coronary syndrome are reviewed. The 99th percentile is an arbitrary cut point and there are many problems associated with its application, including defining a truly healthy population, the difficulty of standardisation of cardiac troponin assays, especially but not only cardiac troponin I, and the effects of age and sex on this parameter. The Emergency Department (ED) screens many more persons for possible acute coronary syndromes than actually have the condition and their needs are best met by a "rule-out" test that enables them to clear their busy departments of the many persons who do not actually have the condition. The needs of the ED are not optimally met using the 99th percentile. The index of individuality for the cardiac troponins is small and significant changes consistent with an acute coronary syndrome can occur without the 99th percentile being exceeded. It appears that the ED may be better served by use of delta troponin changes rather than the 99th percentile, but there are problems with this approach, particularly in persons who present late when troponin release has plateaued. In addition, there are many non-acute coronary syndrome causes for cardiac troponin release. The needs of the cardiologist and the ED physician are so different that it may be inappropriate for both groups to use the same diagnostic criteria for cardiac troponin, and it is of great importance that cardiac troponin measurement be used as only one part of the assessment of the person presenting with possible acute coronary syndrome.

Chimeric recombinant antibody fragments in cardiac troponin I immunoassay

OBJECTIVES

To introduce a novel nanoparticle-based immunoassay for cardiac troponin I (cTnI) utilizing chimeric antibody fragments and to demonstrate that removal of antibody Fc-part and antibody chimerization decrease matrix related interferences.

DESIGN AND METHODS

A sandwich-type immunoassay for cTnI based on recombinant chimeric (mouse variable/human constant) antigen binding (cFab) antibodies and intrinsically fluorescent nanoparticles was developed. To test whether using chimeric antibody fragments helps to avoid matrix related interferences, samples (n=39) with known amounts of triglycerides, bilirubin, rheumatoid factor (RF) or human anti-mouse antibodies (HAMAs) were measured with the novel assay, along with a previously published nanoparticle-based research assay with the same antibody epitopes.

RESULTS

The limit of detection (LoD) was 3.30ng/L. Within-laboratory precision for 29ng/L and 2819ng/L cTnI were 13.7% and 15.9%, respectively. Regression analysis with Siemens ADVIA Centaur® yielded a slope (95% confidence intervals) of 0.18 (0.17-1.19) and a y-intercept of 1.94 (-1.28-3.91) ng/L. When compared to a previously published nanoparticle-based assay, the novel assay showed substantially reduced interference in the tested interference prone samples, 15.4 vs. 51.3%. A rheumatoid factor containing sample was decreased from 241ng/L to <LoD.

CONCLUSIONS

Utilization of cFab-fragments enabled the development of a sensitive (LoD=3.3ng/L) immunoassay for the detection of cTnI and decreased matrix related interferences, thus resulting in a lower number of falsely elevated cTnI-values.

The influence of age on serum concentrations of cardiac troponin I: results in rats, monkeys, and commercial sera

Cardiac troponins serve as serum biomarkers of myocardial injury. The current study examined the influence of age on serum concentrations of cardiac troponin I (cTnI). An ultrasensitive immunoassay was used to monitor cTnI concentrations in Sprague-Dawley (SD) rats and Erythrocebus patas monkeys of different ages. The mean cTnI concentrations were highest in 10-day-old rats compared to 25-, 40-, and 80-day-old SD rats. Cardiomyocyte remodeling was apparent in hearts from 10-day-old SD rats as evident by hypercellularity, irregularly shaped nuclei, and moderate numbers of myocytes undergoing mitosis and apoptosis. The mean concentration of cTnI in 5 newborn monkeys was considerably higher than that of three 1-year-old monkeys. Evidence of cardiomyocyte remodeling was also observed in these newborn hearts (loss of myofibrils and cytoplasmic vacuolation). Commercial animal serum samples were also analyzed. The concentrations of cTnI detected in fetal equine and porcine serum were considerably higher than that found in adult equine and porcine serum samples Likewise, fetal bovine serum had higher cTnI concentrations (>2,400 pg/ml) than did adult caprine and laprine samples (2.5-2.7 pg/ml). The present study found age-related differences in cTnI concentrations, with higher levels occurring at younger ages. This effect was consistent across several animal species.

The global need to define normality: the 99th percentile value of cardiac troponin

BACKGROUND

How to select a presumably normal population for the establishment of 99th percentile cutoffs for cardiac troponin assays has not been adequately addressed. Lack of attention to this question can result in misleading medical decision cutoffs.

CONTENT

From our review of the peer-reviewed literature, including international recommendations, no uniform procedure is followed and no uniform guideline has been published by experts or regulatory agencies to guide researchers or manufacturers of cardiac troponin assays in their quest to define the health or "normality" of a reference population that is used to establish an accurate 99th percentile value. As we progress globally into the era of high-sensitivity cardiac troponin assays, we propose several suggested approaches to define presumably normal individuals by use of clinical and biomarker surrogates.

SUMMARY

Our uniform approach to defining who is normal and who may not be normal will help to define diagnostic and risk outcomes assessments in the management of patients with suspected myocardial injury, both for use in current clinical practice and clinical research, as well as for the potential future use of cardiac troponin in primary prevention.

New insights in the pathophysiology of acute myocardial infarction detectable by a contemporary troponin assay

OBJECTIVES

ST-elevation and non-ST-elevation myocardial infarction (STEMI, NSTEMI) are considered two distinct pathophysiologic entities. We evaluated cardiac troponin I (cTnI) release in STEMI and NSTEMI using a "contemporary" (CV>10 to 20% at the 99th percentile concentration) cTnI assay for patients undergoing early percutaneous coronary intervention (PCI).

DESIGN AND METHODS

856 patients with suspected acute coronary syndrome consecutively admitted to the Emergency Department of the Maggiore Hospital of Novara (225 STEMI and 135 NSTEMI) were selected according to: 1) early (≤ 4 h from admission) and successful PCI; and 2) cTnI measurements at ED presentation and within 24h. The influence of the MI type on cTnI concentrations at baseline and after PCI as well as the velocity of cTnI [cTnI V=absolute increase (after log conversion of cTnI measurements)/delay between the two measurements] was studied by multiple regression analysis, adjusting for patient parameters.

RESULTS

A statistically significant interaction between MI type and time from symptoms was reported on cTnI concentrations (p<0.0001): STEMI and NSTEMI differed for cTnI releases at admission and after revascularization. Higher cTnI V in STEMI was detectable in patients admitted within 6h from symptoms. Baseline cTnI concentrations were lower in patients with a history of coronary artery disease (CAD) and increased with aging (p<0.0001). In the elderly (>75 years), the cTnI V was significantly increased.

CONCLUSION

STEMI and NSTEMI patients have different patterns and dynamics of cTnI release influenced by the interaction with time from symptoms, by aging and history of CAD.

Cardiac troponin assay classification by both clinical and analytical performance characteristics: a study on outcome prediction

BACKGROUND

Cardiac troponin assays have been classified according to whether they measure the 99th percentile concentration of a healthy reference population with imprecision (expressed as CV) of ≤10%, between 10% and 20%, or >20%. Assays in these categories have been deemed "guideline acceptable," "clinically usable," or "not acceptable," respectively. We compared four widely used "clinically usable" cardiac troponin I (cTnI) assays with an assay designated "not acceptable" for accuracy in predicting the clinical outcome of death.

METHODS

Blood was collected from 259 men and 249 women, mean (SD) age 68.8 (17.8) and 70.2 (17.8) years, respectively, admitted to the emergency department for suspected myocardial infarction. We measured cTnI by the Access, Architect, i-Stat, Stratus CS, and VIDAS assays. Deaths in this population were recorded over a 31-month period.

RESULTS

We found VIDAS cTnI assay measurement CVs of 10% and 20% at concentrations of 0.04 and 0.02 μg/L, respectively. Comparing at the 10% CV cutoff concentration, VIDAS cTnI was less sensitive than the Access and Architect assays (P < 0.001) but more sensitive than i-Stat (P < 0.001) and Stratus CS (P < 0.001) in identifying patients with poor outcomes. At the 20% CV cutoff, the VIDAS assay was equivalent to the other assays in identifying patients with poor outcomes.

CONCLUSIONS

For outcome prediction, the VIDAS cTnI assay was clinically equivalent or superior to other cTnI assays judged to be acceptable from a pure analytical standpoint. Thus, comparison of cardiac troponin assays should consider not only analytical performance, but also clinical performance characteristics.

Troponin-Specific Autoantibody Interference in Different Cardiac Troponin I Assay Configurations

BACKGROUND

Autoantibodies to cardiac troponins (cTnAAb) can interfere with the measurement of cardiac troponin I (cTnI) by immunoassays. The aim of this study was to explore the degree of cTnAAb interference in different cTnI assay configurations.

METHODS

Ternary troponin complex was added into samples (serum or plasma, n = 132, 68% cTnAAb positive) from individuals without known cardiac conditions. The recovery of cTnI was then measured with 6 investigational cTnI assays (2, 3, or 4 antibodies per assay). Three of these assays were then selected for further comparison by use of samples (plasma, n = 210, 33% cTnAAb positive) from non–ST-elevation acute coronary syndrome patients in the FRISC-II (FRagmin/Fast Revascularisation during InStability in Coronary artery disease) cohort. Finally, these results were compared to those obtained with 3 commercial cTnI assays.

RESULTS

Analytical recoveries varied widely among the 6 investigational assays. Notably the low recoveries (median 9%) of the midfragment-targeting reference assay were normalized (median 103%) with the use of the 4-antibody assay construct (3 capture, 1 tracer antibody) with only 1 antibody against a midfragment epitope. Reduced analytical recoveries correlated closely with measured autoantibody amounts. cTnI concentrations from cTnAAb-positive patient samples determined with 3 investigational assays confirmed the reduced concentrations expected from the low analytical recoveries. The results from the commercial cTnI assays with antibody selections representative for contemporary assay constructs revealed a similar underestimation (up to 20-fold) of cTnI in cTnAAb-positive samples.

CONCLUSIONS

A novel cTnI assay deviating from the conventional IFCC-recommended midfragment approach substantially improves cTnI detection in samples containing cTnAAbs.

A comprehensive review of upper reference limits reported for (high-)sensitivity cardiac troponin assays: the challenges that lie ahead

Cardiac troponins (cTn) are the preferred markers for the diagnosis of acute myocardial infarction (AMI). The guidelines recommend the use of the 99th percentile upper reference concentration of a healthy population as the diagnostic cut-off for AMI. However, a broad range of upper reference limits is still employed, complicating the diagnosis of AMI. This overview is meant to assist laboratory specialists to define an appropriate cut-off value for the diagnosis of AMI. Therefore, we provide an overview of the analytical performance and upper reference limits of seven (high-)sensitivity cTn assays: Roche high-sensitivity cTnT and ADVIA Centaur, Stratus CS, Dimension Vista, Vitros ECi, Access and Architect cTnI assays. It is shown that none of the reference populations completely met the guidelines, including those in package inserts. Forty percent of the studies collected less than the advised minimum of 300 subjects. Many studies (50%) did not report their inclusion criteria, while lower 99th percentile limits were observed when more stringent selection criteria were applied. Higher troponin cut-offs were found in men and elderly subjects, suggesting sex- and age-specific cut-offs would be considered. Therefore, there is still need for a large, rigorously screened reference population to more accurately establish cTn upper reference limits.

Evaluation of four rapid immunochromatographic tests for the detection of cardiac troponin I

Cardiac troponin I (cTnI) is a sensitive and specific marker of acute coronary syndromes and myocardial damage. During the past few years, it has become the preferred biochemical marker of myocardial infarction. However, due to the sensitivity required for its detection, only automated systems can be used in developed countries. However, these are rather expensive and unaffordable for most laboratories in developing countries. Many manufacturers have therefore proposed rapid immunochromatographic tests to detect cTnI. The aim of this study was to assess the limit of detection (LOD) and performance of four rapid immunochromatographic tests available in Madagascar. The four tests evaluated were Hexagon Troponin, Nadal troponin I cassette, Troponitest+, and Amicheck-Trop. Amicheck-Trop had a sensitivity and negative predictive value of about 80%, whereas for the three others, they were about 20%. The specificity of Amicheck-Trop of 87.3% was lower than the specificities of the other tests (98% to 100%). These differences were explained by the limits of detection of the tests: 0.3 to 0.4 ng/ml for Amicheck-Trop but only 1.8 to 2 ng/ml for the three other tests. It was concluded that Amicheck-Trop could be useful in the management of acute myocardial infarction or myocarditis in sparsely equipped laboratories in developing countries.

Early and late outcome prediction of death in the emergency room setting by point-of-care and laboratory assays of cardiac troponin I

BACKGROUND

Point-of-care (POC) assays of cardiac troponins are common in the emergency department setting. The question raised was as follows: What is the clinical impact of the results of POC assays of cardiac troponins as compared with sensitive laboratory assays?

METHODS

Patients admitted consecutively to the emergency department (N = 1,069) and on whom cardiac troponins were requested as part of their clinical work-up were included. Cardiac troponin I (cTnI) was measured by the POC assays-i-Stat (Abbott Diagnostics, Abbott Park, IL) and Stratus CS (Siemens Healthcare Diagnostics, Deerfield, IL)-and by the laboratory assays-Access AccuTnI (Beckman Coulter, Fullerton, CA) and Architect cTnI (Abbott Diagnostics). Results were related to early (14 days) and late outcome (median 3.3 months, range 0.1-35) as to death.

RESULTS

The laboratory assays identified more patients (P < .001) with elevated levels than the two POC assays (39%-74% vs 20%-27%). Adopting the 99th percentiles upper reference limit, the Access AccuTnI identified 88% and Architect cTnI identified 81% of all patients who died of cardiovascular disease as compared with 50% and 54% for i-Stat and Stratus CS, respectively (P < .001). Negative predictive values for the laboratory assays were 97% as compared with 89% to 93% for the POC assays. Negative likelihood ratios were 0.25 (CI 0.15-0.041) and 0.59 to 0.68 (CI 0.47-0.79), respectively.

CONCLUSIONS

The current POC cTnI assays are less sensitive for outcome prediction of patients with myocardial injury. The clinical judgment of the patient with suspected myocardial ischemia should not solely rely on results from POC assays. If a clinical suspicion of myocardial injury remains despite negative cTnI results with the POC assays, such results should be complemented by results from sensitive laboratory assays.

Normal plasma levels of cardiac troponin I measured by the high-sensitivity cardiac troponin I access prototype assay and the impact on the diagnosis of myocardial ischemia

OBJECTIVES

This study sought to evaluate the analytical and clinical performance of the novel hypersensitive cardiac troponin I (cTnI) prototype assay from Beckman Coulter (Fullerton, California).

BACKGROUND

Studies on patients with acute coronary syndromes and on seemingly healthy subjects have shown that even very minor elevations of cardiac troponins are associated with an increased risk of death. However, the normal plasma levels of cardiac troponins are still not known.

METHODS

cTnI plasma levels were measured in 542 healthy subjects, 319 men (age 59.9 +/- 11.8 years) and 213 women (age 59.8 +/- 13.1 years), and in 1,503 randomly selected patients of the GUSTO IV (Global Utilization of Strategies To open Occluded arteries IV) cohort with unstable angina and non-ST-segment elevation myocardial infarctions (MIs).

RESULTS

The cTnI levels at 10% coefficient of variation and 20% coefficient of variation imprecision were 0.0033 and 0.0016 microg/l, respectively. The cTnI levels were measurable in >95% of the healthy subjects. The median level of healthy subjects <60 years of age was 0.0032 microg/l (range 0.0011 to 0.0079 microg/l) with the 99th percentile being 0.010 microg/l. No sex differences were observed. A receiver-operator characteristic curve analysis showed an optimal discrimination between healthy subjects and patients at 0.0064 microg/l with a sensitivity of 84.8% (95% confidence interval: 82.8% to 86.6%) and specificity of 89.7% (95% confidence interval: 86.8% to 92.2%). Outcomes as to death and/or MI were significantly different at this level (p < 0.01) in the GUSTO IV cohort.

CONCLUSIONS

The novel high-sensitivity cTnI prototype assay from Beckman Coulter allows for the first time the measurement of cTnI levels in almost all healthy subjects. Our data indicate that the assay may be a powerful aid in the diagnosis and outcome prediction of patients with suspected myocardial ischemia and question any definition of myocardial infarction.

Imprecision of cardiac marker analyses among laboratories on the basis of external quality assurance results: Finnish experience

The purpose of this report was to evaluate the reproducibility and harmonization of cardiac marker tests and to describe the current situation concerning quality of assays for cardiac markers on the basis of the results of the external quality control schemes (EQAS) of Labquality Ltd., Helsinki, Finland in the period 2002 to 2005. Finnish EQAS surveys obtained for proficiency samples at low marker concentration indicated that the overall coefficient of variation (CV) between laboratories for CK-MBmass and troponin I exceeded 10 %, while for cardiac troponin T the CV was 8.6 %. Intra-laboratory reproducibility was investigated in a single laboratory using concomitant testing in the same EDTA plasma samples to establish cut-off limits for one CK-MBmass and three troponin assays. The 10 % imprecision limit obtained from the concomitant testing in the same samples for CK-MBmass was (by Elecsys) 8.5 microg/L, for cardiac troponin T (by Elecsys) 0.023 microg/L and for cardiac troponin I (by AxSYM) and by Immulite 2000) 0.85 microg/L and 0.63 microg/L. At present, it is recommended that laboratories determine the concentration at which the 10 % imprecision for a specific cardiac marker assay is reached, because the assays generally do not reach that imprecision at the level of the 99th percentile value, usually taken as decisional level. However, common efforts of scientific societies and professional diagnostic industry associations internationally are needed if consensus is to be reached on standardization of immunoassays for cardiac markers and uniform results obtained among laboratories.

Aborted myocardial infarction: is it real in the troponin era?

BACKGROUND

Cardiac troponins are the markers of choice for the diagnosis of acute myocardial infarction. The objective of this study was to compare the frequency of "aborted myocardial infarction" (no detectable myocardial injury) determined by measurement of troponin versus that determined by creatine kinase (CK) and creatine kinase-muscle brain (CK-MB) measurement criteria among patients with ST-elevation myocardial infarction (STEMI) who received reperfusion therapy.

METHODS

Since 2004, the Mayo Clinic (Rochester, MN) has had a standard reperfusion protocol for the treatment of patients with STEMI. During the study period, 767 patients presented with new or presumed new ST elevation or left bundle block.

RESULTS

The diagnosis of STEMI was confirmed in 765 (99.7%) patients. Using the 99th percentile cutoff value, troponin T elevations occurred in 765 (100%) of 765 patients when serial samples were available. Creatine kinase-MB levels of twice or more the upper limit of normal occurred in 681 (90.1%) of 749 patients with serial samples for CK-MB, and CK equal or greater than twice the gender-specific upper limits of normal occurred in 521 (78.8%) of 661 patients with serial samples for CK available.

CONCLUSION

The frequency of aborted myocardial infarction is 0% when using troponin at the 99th percentile cutoff as recommended by contemporary guidelines from the European Society of Cardiology (Nice, France) and American College of Cardiology (Washington, DC).

Value of Cardiac Troponin I Cutoff Concentrations below the 99th Percentile for Clinical Decision-Making

Background: The aim of this study was to evaluate factors influencing the 99th percentile for cardiac troponin I (cTnI) when this cutoff value is established on a highly sensitive assay, and to compare the value of this cutoff to that of lower cutoffs in the prognostic assessment of patients with coronary artery disease.

Methods: We used the recently refined Access AccuTnI assay (Beckman-Coulter) to assess the distribution of cTnI results in a community population of elderly individuals [PIVUS (Prospective Study of the Vasculature in Uppsala Seniors) study; n = 1005]. The utility of predefined cTnI cutoffs for risk stratification was then evaluated in 952 patients from the FRISC II (FRagmin and Fast Revascularization during InStability in Coronary artery disease) study at 6 months after these patients had suffered acute coronary syndrome.

Results: Selection of assay results from a subcohort of PIVUS participants without cardiovascular disease resulted in a decrease of the 99th percentile from 0.044 μg/L to 0.028 μg/L. Men had higher rates of cTnI elevation with respect to the tested thresholds. Whereas the 99th percentile cutoff was not found to be a useful prognostic indicator for 5-year mortality, both the 90th percentile (hazard ratio 3.1; 95% CI 1.9–5.1) and the 75th percentile (hazard ratio 2.8; 95% CI 1.7–4.7) provided useful prognostic information. Sex-specific cutoffs did not improve risk prediction.

Conclusions: The 99th percentile of cTnI depends highly on the characteristics of the reference population from which it is determined. This dependence on the reference population may affect the appropriateness of clinical conclusions based on this threshold. However, cTnI cutoffs below the 99th percentile seem to provide better prognostic discrimination in stabilized acute coronary syndrome patients and therefore may be preferable for risk stratification.

Clinical Performance of Two Highly Sensitive Cardiac Troponin I Assays

Background: The aim of this study was to compare the clinical performance of 2 sensitive cTnI assays with 10% CV imprecision below the 99th percentile upper reference limit.

Methods: We measured cardiac troponin and N-terminal pro-brain natriuretic peptide (NT-proBNP) concentrations in a random sample of the Global Use of Strategies To Open Occluded Coronary Arteries (GUSTO) IV cohort (n = 1251). Outcome data of 1-year mortality and the composite endpoint DMI [death and/or myocardial infarction (MI) within 30 days] were available in all patients. The 99th percentile of a healthy population was estimated from the Sweden Women and Men and Ischemic Heart Disease (SWISCH) cohort (n = 442). We measured cardiac troponin I (cTnI) using the Access AccuTnI (Beckman Coulter) and Centaur TnI Ultra (Siemens Healthcare Diagnostics) and NT-proBNP using the Elecsys 2010 (Roche Diagnostics).

Results: Applying the 10% CV cutoff, the sensitivity of the Access AccuTnI assay in identifying DMI and death was higher than that of the Centaur TnI Ultra (P = 0.02 and P &lt; 0.001), and the AccuTnI assay also identified more patients at risk (P &lt; 0.001) and with poor outcome. Applying the 99th percentile cutoffs, AccuTnI identified more patients at risk than the Centaur TnI (P &lt; 0.001) and with significant differences in outcome. Significantly more patients with cardiac troponins below the cutoffs as measured by Centaur TnI had increased NT-proBNP concentrations (P &lt; 0.001) compared with AccuTnI.

Conclusions: The AccuTnI assay identified more patients at risk than the Centaur cTnI Ultra assay. Our results demonstrate the clinical potential of high-sensitivity cardiac troponin assays for the identification of patients at risk of dying from cardiovascular disease.

Present and Future Biochemical Markers for Detection of Acute Coronary Syndrome

The use of biochemical markers in the diagnosis and management of patients with acute coronary syndrome has increased continually in recent decades. The development of highly sensitive and cardiac-specific troponin assays has changed the view on diagnosis of myocardial infarction and also extended the role of biochemical markers of necrosis into risk stratification and guidance for treatment. The consensus definition of myocardial infarction places increased emphasis on cardiac marker testing, with cardiac troponin replacing creatine kinase MB as the "gold standard" for diagnosis of myocardial infarction. Along with advances in the use of more cardiac-specific markers of myocardial necrosis, biochemical markers that are involved in the progression of atherosclerotic plaques to the vulnerable state or that signal the presence of vulnerable plaques have recently been identified. These markers have variable abilities to predict the risk of an individual for acute coronary syndrome. The aim of this review is to provide an overview of the well-established markers of myocardial necrosis, with a special focus on cardiac troponin I, together with a summary of some of the potential future markers of inflammation, plaque instability, and ischemia.

Cardiac troponin I measurement using the ACS:180 to predict four-year cardiac event rate

Background

This study aimed at evaluating the ability of cardiac troponin I (cTnI) measurement on the ACS:180 for prognostic risk stratification. Sequential admissions to the coronary care unit of a busy district general hospital were studied. All patients were followed up for a maximum of 4.3 years and cardiac events, either cardiac death, readmission with acute myocardial infarction or admission with acute unstable angina were documented.

Methods

Blood samples were taken on admission and at 4 and 12 h. A serum aliquot was taken and stored frozen at −70oC. The frozen aliquots were subsequently analysed for cTnI by chemiluminescent immunoassay using an ACS:180. Patients were categorized into those with or without ST segment elevation on the presenting electrocardiogram. The optimized decision threshold for mortality and event prediction was then determined by log-rank analysis and by construction of Kaplan-Meier survival plots.

Results

A total of 289 patients (196 men) median age 65.3 years, range 27.4–87.9 years were studied. Out of this, 139 had ST elevation myocardial infarction (STEMI) and 150 had suspected non-STEMI (NSTEMI). Full data were available from 278 patients. Admission cTnI did not predict any of the endpoints in the STEMI group. In patients admitted with suspected NSTEMI, admission and peak cTnI predicted increased risk of death or readmission with acute myocardial infarction. In addition, peak cTnI predicted increased risk of death.

Conclusion

A cTnI exceeding 0.16 μg/L on admission or during hospital stay predicted an increased cardiac event rate at four years in patients admitted with suspected NSTEMI.

Combined measurements of N-terminal pro-brain natriuretic peptide and cardiac troponins in potential organ donors

OBJECTIVE

Brain death may induce cardiac dysfunction. In potential organ donors measurements of N-terminal pro-brain natriuretic peptide (NT-proBNP) and circulating cardiac troponins T and I (cTnT and cTnI), alone or in combination, are performed to investigate the accuracy of these biomarkers for early diagnosis of left ventricular systolic dysfunction.

DESIGN AND SETTING

Prospective study in a multidisciplinary intensive care unit of an university hospital.

PATIENTS

63 brain-dead patients scheduled for multiple organ harvesting.

MEASUREMENTS AND RESULTS

We measured NT-proBNP, cTnT, and cTnI and determined fractional area change (FAC) using transesophageal echocardiography. Forty-five patients had normal FAC, 9 a moderate decrease in FAC (30-50), and 9 a severe decrease in FAC (<or=30%). NT-proBNP and cTnT concentrations were significantly higher in patients with a severe decrease in FAC than in those with a moderate decrease. Combining measurements of these two biomarkers, the sensitivity of the test to predict severe decrease in FAC increased significantly to reach 1.00 compared with the sensitivities of individual measurements. The ROC curve area of combined measurements of NT-proBNP and cTnT was significantly higher than single measurements: 0.87 vs. 0.82 for NT-proBNP, 0.78 for cTnT, and 0.72 for cTnI.

CONCLUSIONS

In potential organ donors the combined measurement of NT-proBNP and cTnT concentrations is more accurate than individual measurement of NT-proBNP, cTnT, and cTnI in the early diagnosis of severe left ventricular systolic dysfunction. These findings may lead to improve the quality of cardiac care of the potential organ donors.

The Antibody Configurations of Cardiac Troponin I Assays May Determine Their Clinical Performance

Background: Previous studies have shown superior clinical performance of the cardiac troponin I (cTnI) assay from Beckman-Coulter Diagnostics. This assay had a unique combination of monoclonal antibodies with 2 monoclonal antibodies directed against epitopes near the NH2 terminus of the heart-specific region of troponin I. The approach has been adopted by the new cTnI assay from Abbott Diagnostics. The aim of our study was to investigate whether this approach affects the clinical performance of cTnI assays.

Methods: Cardiac troponin concentrations were measured in a random sample of patients with unstable coronary artery disease included in the GUSTO IV trial (n = 696) by the AccuTnI (Beckman-Coulter Diagnostics), Architect cTnI (Abbott Diagnostics), Immulite 2500 cTnI (Diagnostics Products Corporation), and Elecsys 2010 cTnT (Roche Diagnostics) assays and related to the 1-year mortality. The primary cutoff concentrations were based on the 99th percentile upper reference limits and an imprecision (CV) ≤10%.

Results: The sensitivities of the AccuTnI and Architect cTnI assays in identifying patients who died within 1 year were equal and were significantly higher (P &lt;0.05) than those of the Immulite 2500 cTnI and the Elecsys cTnT assays. The concordance between the AccuTnI and Architect cTnI assays was 97%, but concordances between the Architect cTnI and the Elecsys cTnT assays were 89%–92% with more at-risk patients (P &lt;0.01 to P &lt;0.001) identified by the Architect cTnI assay.

Conclusions: The Architect cTnI assay has clinical performance similar to that of the AccuTnI, probably as a result of the inclusion of a monoclonal antibody against troponin I epitope 41–49 in the assay.

Comparison of Cardiac Troponin I Immunoassays Variably Affected by Circulating Autoantibodies

Background: We recently provided evidence that circulating autoantibodies against cardiac troponin I (cTnI) or the troponin complex cause negative interference in cTnI immunoassays. By comparing three cTnI immunoassays, we further explored the phenomenon of circulating autoantibodies and their consequences in patient samples.

Methods: We developed a cTnI immunoassay with a novel assay design using three antibodies, two of which bind epitopes outside the stable, central part of cTnI. Samples from 541 chest pain patients were measured with the new cTnI assay and with a first-generation cTnI assay (Innotrac Aio cTnI) using a conventional midfragment assay design. Using another sample cohort, we also compared the new assay with a second-generation cTnI assay (Access AccuTnI).

Results: The analytical detection limit of the new cTnI assay was 0.012 μg/L, and the lowest concentration giving a total imprecision (CV) of 10% was 0.060 μg/L. The mean difference (95% limits of agreement) between the new cTnI and Aio cTnI assays was larger in admission samples (21.0%; −107.8% to 149.7%) than in samples taken 6–12 h (12.8%; −61.5% to 87.2%) and 24 h after admission (3.0%; −71.3% to 77.4%; P &lt;0.001). With the lowest concentrations giving 10% CV (0.22 μg/L for Aio cTnI) used as cutoffs, 14.3% (n = 76) of admission samples were positive only with the new assay, whereas 13.5% (n = 72) were positive with both assays. Of samples taken at 6–12 and 24 h, 10.2% (n = 31) and 8.3% (n = 29) were positive only with the new assay. ROC curve analysis of admission samples showed a significantly higher area under the curve for the new cTnI assay (0.940) than for the Aio cTnI assay (0.846; P &lt;0.001). The new cTnI assay gave generally lower results than the AccuTnI assay; the mean (95% limits of agreement) differences were −58.9% (−151.8% to 34.0%) in admission samples. In samples with severe interference from autoantibodies, median ratios between the new assay and AccuTnI were higher than in samples with no apparent troponin autoantibodies (0.875 vs 0.481; P&lt;0.001).

Conclusions: The new cTnI assay, which is based on a novel antibody combination different from the conventional midfragment antibody approach, offers improved detection of cTnI in samples containing troponin autoantibodies.

Multicenter evaluation of analytical performance of the Liaison® troponin I assay

OBJECTIVES

This study evaluated the analytical characteristics of the Liaison immunoassay for cardiac troponin I (cTnI).

DESIGN AND METHODS

The protocol consisted of eight sections: evaluation of antibody specificity, linearity, detection limit and imprecision, method comparison, evaluation of endogenous interferents, anticoagulant interference, sample stability, and reference values.

RESULTS

The assay equally measured free and complexed cTnI. The minimum detectable cTnI concentration was 0.021 microg/l. The cTnI concentration corresponding to a total CV of 10% was 0.056 microg/l. Linearity of response was demonstrated along the entire dynamic range of the assay. Assay interferences were minimal. cTnI concentrations in serum and heparinized plasma were significantly different. Values in EDTA plasma were on average approximately 5% higher than in matched serum, but this difference was not significant. The 99th percentile cTnI value in healthy subjects was 0.036 microg/l.

CONCLUSIONS

Being sensitive, specific, and precise, the Liaison cTnI assay meets current requirements to aid in the diagnosis of myocardial necrosis.

British Cardiac Society Working Group on the definition of myocardial infarction

The British Cardiac Society commissioned this report to help address inconsistencies in the terminology for acute coronary syndromes and wide variations in the threshold for the diagnosis of myocardial infarction (MI) depending on the assay performed, the precision, and the sensitivity. In addition, several publications have highlighted potential problems with the application of the European Society of Cardiology(ESC)/American College of Cardiology (ACC) consensus document published in 2000. A revision process has been initiated under the guidance of the ESC, the ACC, and the American Heart Association (AHA). The purpose of this report is to help inform the next revision of the ESC/ACC/AHA guidelines for the diagnosis of MI.

An interfering component in cardiac troponin I immunoassays—Its nature and inhibiting effect on the binding of antibodies against different epitopes

OBJECTIVES

We recently reported on the occurrence of a common interfering factor (IF) that negatively affects determinations of cardiac troponin I (cTnI). The aim of the present investigation was to extend our initial finding by a detailed epitope-based determination of the location of IF and to reveal the approximate size and characteristics of IF.

DESIGN AND METHODS

Two-site immunoassays using combinations of 16 monoclonal and 2 polyclonal cTnI antibodies and 1 monoclonal troponin C (TnC) antibody were used to measure the analytical recovery of cTnI or cTnI-TnC in serum samples. Gel filtration of serum samples containing IF was performed and the analytical recovery of cTnI in the fractions was determined. EDTA-plasma samples to which cTnI had been added and serum samples containing endogenous cTnI were also separated by gel filtration.

RESULTS

The mean analytical recoveries of cTnI were 28.3% (range 7.5-55.1%) and of cTnI-TnC were 23.5% (range 8.7-51.8%) in samples containing IF when antibodies against midfragment epitopes of cTnI were used. The mean recovery of cTnI was 65.1% and 73.3% for antibodies with N- and C-terminal epitopes. Gel filtration of samples with low recovery of cTnI showed that the approximate molecular mass of IF was 50-200 kDa and that the cTnI elution profiles of samples containing IF were shifted towards higher molecular mass compared with samples with less IF.

CONCLUSIONS

Antibodies against midfragment epitopes of cTnI are affected by IF to a considerable but variable extent, and the presence of IF can be demonstrated by gel filtration.