In-Vitro Diagnostic Reagent Evaluation of Commercially Available Cardiac Troponin I Assay Kits Using H/D Exchange Mass Spectrometry for Antibody-Epitope Mapping

Cardiac troponin I (cTnI) is the biomarker of choice and considered a gold standard for the diagnosis of acute myocardial infarction. However, the quantitative results of cTnI assay kits from different manufacturers are not comparable. Based on the H/D exchange mass spectrometry (HDX-MS) workflow, we developed an in-vitro diagnostic reagent antibody evaluation strategy to analyze the interactions of epitopes and antibody cocktails─(R195, F12, S13) and (D1, D2, pAb2). The HDX results indicate that the quantitative result bias of the different reagents originates from the ability of antibodies to recognize various cTnI complex forms, such as free cTnI, hydrolyzed cTnI, and cTnI combined with cTnT or TnC as binary or ternary complexes (cTnIC, cTnTIC), in blood based on different epitopes. The data obtained from the peptide HDX of interest after treatment with various antibody cocktails clearly indicated epitope specificity. The consistency of quantitative results can be improved by a thorough investigation into the epitopes recognized by the antibodies of various diagnostic kits, which will lead to the standardization of cTnI diagnosis.

Sensitive Cardiac Troponins: Could They Be New Biomarkers in Pediatric Pulmonary Hypertension Due to Congenital Heart Disease?

To analyze the role of sensitive cardiac troponin I (scTnI) and high-sensitive troponin T (hscTnT) in the determination of myocardial injury caused by volume and pressure load due to pulmonary hypertension (PH) and to investigate if these markers may be useful in the management of PH in childhood. Twenty-eight patients with congenital heart disease (CHD) with left to right shunt and PH, 29 patients with CHD with left to right shunt but without PH, and 18 healthy children, in total 75 individuals, were included in the study. All cases were aged between 4 and 36 months. Echocardiographic evaluation was performed in all cases, and invasive hemodynamic investigation was performed in 33 cases. Blood samples were obtained from all cases, for the measurement of brain natriuretic peptide (BNP), pro-brain natriuretic peptide (pro-BNP), sensitive cardiac troponin I (scTnI), and high-sensitive troponin T (hscTnT) levels. The mean BNP, pro-BNP, scTnI, and hsTnT levels were statistically significantly higher in patients with PH than in the patients without PH (p < 0.001). A statistically significant positive correlation was determined between pulmonary artery systolic pressure and scTnI and hscTnT levels (r = 0.34 p = 0.01, r = 0.46 p < 0.001, respectively) levels. Pulmonary hypertension determined in congenital heart diseases triggers myocardial damage independently of increased volume or pressure load and resistance, occurring by disrupting the perfusion via increasing ventricular wall tension and the myocardial oxygen requirement. Serum scTnI and hscTnT levels may be helpful markers to determine the damage associated with PH in childhood.

Plasma Troponin Levels after Cardiac Surgery vs after Myocardial Infarction

Raised plasma troponin, a diagnostic marker for myocardial infarction, usually occurs after cardiac surgery, leading to difficulties in diagnosing postoperative myocardial infarction. To ascertain whether the same processes influence troponin elevation in both conditions, a literature search was performed for plasma troponin elimination curves after myocardial infarction, myocardial infarction with reperfusion, and cardiac surgery. From 70 studies, 11 curves using the Stratus immunoassay kit were analyzed: 5 post-cardiac surgery (412 patients), 2 after myocardial infarction with reperfusion (169 patients), and 4 after myocardial infarction (640 patients). For each group, a new plot was formulated from the mean troponin level at each time interval. While the up-slope of the cardiac surgery curve was much steeper than that of myocardial infarction, resembling that of myocardial infarction with reperfusion, its down-slope was significantly more gentle than that of both other groups (−0.91 vs −5.31, t = 3.47, df = 8, p < 0.01). This suggests that postoperative troponin elevation involves enhanced cell permeability as seen after ischemia reperfusion rather than permanent cellular damage. The gentler down-slope may point to surgery-induced impaired troponin removal from the circulation. Due to the different mechanisms proposed, implications from post-myocardial infarction troponin levels may not be conferred on post-cardiac surgery patients.

Epitope mapping and targeted quantitation of the cardiac biomarker troponin by SID-MRM mass spectrometry

The absolute quantitation of the targeted protein using MS provides a promising method to evaluate/verify biomarkers used in clinical diagnostics. In this study, a cardiac biomarker, troponin I (TnI), was used as a model protein for method development. The epitope peptide of TnI was characterized by epitope excision followed with LC/MS/MS method and acted as the surrogate peptide for the targeted protein quantitation. The MRM-based MS assay using a stable internal standard that improved the selectivity, specificity, and sensitivity of the protein quantitation. Also, plasma albumin depletion and affinity enrichment of TnI by anti-TnI mAb-coated microparticles reduced the sample complexity, enhanced the dynamic range, and further improved the detecting sensitivity of the targeted protein in the biological matrix. Therefore, quantitation of TnI, a low abundant protein in human plasma, has demonstrated the applicability of the targeted protein quantitation strategy through its epitope peptide determined by epitope mapping method.

An assessment of the concentration-related prognostic value of cardiac troponin I following acute coronary syndrome

In 2004 the British Cardiac Society redefined myocardial infarction by cardiac troponin I (cTnI) concentration: ≤ 0.06 μg/L (unstable angina), >0.06 to < 0.5 μg/L (myocardial necrosis), and ≥ 0.5 μg/L (myocardial infarction). We investigated the effects of this classification on all-cause mortality in 1,285 patients from the Evaluation of the Methods and Management of Acute Coronary Events (EMMACE)-2 registry. There were 528 deaths (6.6-year all-cause mortality 41.1%). Survival was greatest in the cTnI ≤ 0.06-μg/L subgroup at 30 days (p = 0.005), 6 months (p = 0.015), 1 year (p = 0.002), and 6.6 years (p = 0.045). After adjustment there was no significant difference in survival between the cTnI >0.06- to < 0.5-μg/L and ≥ 0.5-μg/L subgroups. Increased mortality (hazard ratio, 95% confidence interval) was associated with ages 70 to 80 years (2.58, 1.17 to 3.91) and >80 years (3.30, 3.50 to 5.06), peripheral vascular disease (1.50, 1.16 to 1.94), heart failure (1.36, 1.05 to 1.83), diabetes mellitus (1.68, 1.36 to 2.07), severe left ventricular systolic dysfunction (1.50, 1.00 to 2.21), and creatinine per 10 μmol/L (1.65, 1.02 to 1.08), whereas ages 50 to 60 years (0.55, 0.32 to 0.96), β blockers (0.53, 0.44 to 0.64), aspirin (0.80 0.65 to 0.99), angiotensin-converting enzyme inhibitors (0.67, 0.56 to 0.80), statins (0.73, 0.59 to 0.90), and revascularization (0.33, 0.12 to 0.92) were associated with a lower risk of death. In conclusion, although quantitative evaluation of cTnI concentration in patients with acute coronary syndrome with cTnI > 0.06 μg/L was associated with no added prognostic information, the dichotomization of patients by cTnI status ("positive" and "negative") facilitates acute coronary syndrome risk stratification.

Measurement of cardiac troponin I utilizing a point of care analyzer in healthy alpacas

BACKGROUND

Myocardial disease in camelids is poorly characterized. Nutritional (selenium deficiency) and toxic (ionophore toxicity) myocardial disease have been reported in camelids. Diagnosis and management of these and other myocardial diseases might be enhanced by evaluating cardiac troponin I (cTnI) concentrations. No information about cTnI reference intervals in camelids is currently available.

HYPOTHESIS/OBJECTIVES

(A) To determine cTnI concentrations obtained using a point of care i-STAT(®)1 analyzer (Heska Corporation) in healthy alpacas; (B) to compare alpaca cTnI concentrations between heparinized whole blood and plasma samples and between 2 different storage conditions (4 °C for 24 h or -80 °C for 30 days); (C) to examine assay reproducibility using the i-STAT(®)1.

ANIMALS, MATERIALS AND METHODS

23 healthy alpacas were evaluated. Blood and plasma samples were analyzed by the i-STAT(®)1 within 1 h of collection. Aliquots of plasma were stored at either 4 °C for 24 h or -80 °C for 30 days, and then analyzed. Assay reproducibility was determined by comparing 2 plasma or whole blood cTnI concentrations measured on the same sample over a 10 min period.

RESULTS

Analyzer-specific plasma cTnI concentrations in clinically normal alpacas had a median of <0.02 ng/mL (range: <0.02 ng/mL to 0.07 ng/mL). Plasma and whole blood concentrations showed good agreement. Storage did not affect cTnI concentrations (p > 0.75). Plasma cTnI concentrations had coefficient of repeatability of 0.02 ng/mL.

CONCLUSIONS

The i-STAT(®)1 can measure cTnI in alpacas on both plasma and whole blood and provides similar values for both samples. Storage at 4 °C for 24 h or -80 °C for 30 days does not affect estimates of plasma cTnI. Evaluation of cTnI might be of value in assessing cardiac disease in this species.

Biochemical markers in acute coronary syndrome

Owing to their higher risk for cardiac death or ischemic complications, patients with acute coronary syndrome (ACS) must be identified from other causes of chest pain. Patients with acute coronary syndrome are divided into categories based on their electrocardiogram; those with new ST-segment elevation and those who present with ST-segment depression. The subgroups of patients with ST-segment elevation are candidates for immediate reperfusion, while fibrinolysis appears harmful for those with non-ST elevation myocardial infarction. There is increasing evidence to encourage appropriate risk stratification before deciding on a management strategy (invasive or conservative) for each patient. The TIMI, GRACE or PURSUIT risk models are recommended as useful for decisions regarding therapeutic options. Cardiac biomarkers are useful additions to these clinical tools to correctly risk stratify ACS patients. Cardiac troponin is the biomarker of choice to detect myocardial necrosis and is central to the universal definition of myocardial infarction. The introduction of troponin assays with a lower limit of detection will allow for earlier diagnosis of patients who present with chest pain. Analytical and clinical validations of these new assays are currently in progress. The question is whether the lower detection limit of the troponin assays will be able to indicate myocardial ischemia in the absence of myocardial necrosis. Previous to the development of ultrasensitive cardiac troponin assays free fatty acids unbound to albumin and ischemia modified albumin were proposed as biochemical markers of ischemia. Advances in our knowledge of the pathogenesis of acute coronary thrombosis have stimulated the development of new biomarkers. Markers of left ventricular performance (N-terminal pro-brain natriuretic peptide) and inflammation (e.g. C-reactive protein) are generally recognized as risk indicators. Studies suggest that using a number of biomarkers clinicians can risk stratify patients over a broad range of short and long term cardiac events. Nevertheless, it is still under debate as to which biomarker combination is best preferred for risk prediction. This review will focus on recent practice guidelines for the management of patients with ACS as well as current advances in cardiac biomarkers, their integration into clinical care and their diagnostic, prognostic and therapeutic utility.

Unusual towering elevation of troponin I after ST-elevation myocardial infarction and intensive monitoring with echocardiography post-percutaneous coronary intervention: a case report

Introduction

The elevation of troponin levels directly corresponds to the extent of myocardial injury. Here we present a case of a robust rise in cardiac biomarkers that correspond to extensive damage to the myocardium but did not spell doom for our patient. It is important to note that, to the best of our knowledge, this is the highest level of troponin I ever reported in the literature after a myocardial injury in an acute setting.

Case presentation

A 53-year-old African American man with an unknown medical history presented to the emergency room of our hospital with chest pain associated with diaphoresis and altered mental status. He required emergency intubation due to acute respiratory failure and circulatory collapse within 10 minutes of his arrival. He was started on heparin and eptifibatide (Integrilin) drips but he was taken immediately for cardiac catheterization, which showed a total occlusion of his proximal left anterior descending, diffuse left circumflex disease and severe left ventricular dysfunction with segmental wall motion abnormality. He remained hypotensive throughout the procedure and an intra-aortic balloon pump was inserted for circulatory support. His urinary toxicology examination result was positive for cocaine metabolites. Serial echocardiograms showed an akinetic apex, a severely hypokinetic septum, and severe systolic dysfunction of his left ventricle. Our patient stayed at the Coronary Care Unit for a total of 15 days before he was finally discharged.

Conclusion

Studies demonstrate that an increase of 1 ng/ml in the cardiac troponin I level is associated with a significant increase in the risk ratio for death. The elevation of troponin I to 515 ng/ml in our patient is an unusual robust presentation which may reflect a composite of myocyte necrosis and reperfusion but without short-term mortality. Nevertheless, prolonged close monitoring is required for better outcome. We also emphasize the need for the troponin assays to be standardized and have universal cutoffs for comparisons across available data.

Experimental Rayless Goldenrod (Isocoma pluriflora) Toxicosis in Goats

Rayless goldenrod ( Isocoma pluriflora) sporadically poisons livestock in the southwestern United States. Similarities with white snakeroot ( Ageratina altissima) poisoning and nearly identical chemical analyses led early researchers to conclude that tremetol, a mixture of benzofuran ketones, is the rayless goldenrod toxin. The toxicity of these ketone toxins have not been fully characterized nor are the pathogenesis and sequelae of poisoning completely understood. The objective of the current study was to characterize and describe the clinical and pathologic changes of rayless goldenrod toxicity in goats. Fifteen goats were gavaged with rayless goldenrod to obtain benzofuran ketone doses of 0, 10, 20, 40, and 60 mg/kg/day. After 7 treatment days, the goats were euthanized, necropsied, and tissues were processed for microscopic studies. After 5 or 6 days of treatment, the 40-mg/kg and 60-mg/kg goats were reluctant to move, stood with an erect stance, and became exercise intolerant. They had increased resting heart rate, prolonged recovery following exercise, and increased serum aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and creatinine kinase activities. All treated animals developed skeletal myopathy with dose-related distribution and severity. The goats dosed with 20 mg/kg and higher also developed myocardial degeneration and necrosis. Although skeletal myonecrosis was patchy and widely distributed, the quadriceps femoris was consistently damaged, even in low-dosed animals. Myocardial lesions were most severe in the papillary muscles of 60-mg/kg—dosed animals. This indicates that goats are highly susceptible to rayless goldenrod poisoning, and that the characteristic lesion of poisoning is skeletal and cardiac myonecrosis.

Evaluating the role of elevated levels of troponin in acute ischemic stroke

Ischemic heart disease and cerebrovascular diseases may coexist in the same patient, and similar risk factors are shared. However, for several years, experimental and observational data have incessantly indicated that neurologically induced myocardial injury exists. This leaves the clinician with a diagnostic dilemma of how to distinguish between neurologically induced myocardial injury and myocardial infarction prior to the stroke. Since various alterations of the ECG have also been reported in this patient category, it has been suggested that elevated troponin levels are somehow neurologically mediated, thus not resulting from direct cardiac release. This review focuses on the available studies that systematically measured troponin in patients with acute ischemic stroke in order to properly interpret troponin elevations in these patients.

Comparison of site-reported and core laboratory-reported creatine kinase-MB values in non-ST-segment elevation acute coronary syndrome (from the international trial SYNERGY)

The effect of nonstandardized creatine kinase (CK)-MB assays on the assessment of myocardial infarction (MI) end points in multicenter international trials has not been evaluated. We compared the site-reported and corresponding core laboratory CK-MB measures from 5 countries participating in the Superior Yield of the New Strategy of Enoxaparin, Revascularization, and Glycoprotein IIb/IIIa Inhibitors (SYNERGY) trial. Samples for CK-MB were collected locally, with corresponding samples sent to a core laboratory at enrollment and after recurrent ischemic events, percutaneous coronary intervention, or coronary artery bypass grafting. The measured values were compared to the reported assay upper limits of normal (ULN) used at the site (or core laboratory for the core laboratory samples). The CK-MB results were available locally and from the core laboratory for 913 patients, constituting 4,693 time-matched laboratory values. The agreement between the core and site laboratory CK-MB/ULN ratio was moderate (concordance correlation coefficient 0.45) and varied considerably by geographic location and site. The CK-MB values were elevated (>or=2 times the ULN) by the core laboratory but normal (<2 times the ULN) by local standards in 708 instances (15%). There were 162 MI end points according to the core laboratory values versus 91 MI end points using the site-reported CK-MB data (kappa statistic 0.48). Compared with patients with no MI by the core or site laboratory values, patients with MI, as determined by both the core and the site laboratories, had significantly lower unadjusted 1-year survival rates (80.6% vs 93.5%, p <0.0001). Patients with MI, as determined by the core laboratory but not by the site laboratory, showed a trend toward a lower 1-year survival rate (89.8% vs 93.5%, p = 0.20). In conclusion, a substantial variation in CK-MB ratios and MI outcomes between the site and core laboratory data was observed in the SYNERGY trial. More MI outcomes were identified by the core laboratory, and patients with MI as defined by core laboratory data had lower 1-year survival, making these events potentially clinically important.

Cardiac markers: a clear cause for point-of-care testing

Point-of-care testing (POCT) in patients with ischemic heart disease is driven by the time-critical need for fast, specific, and accurate results to initiate therapy instantly. According to current guidelines, the results of the cardiac marker testing should be available to the physician within 30 min ("vein-to-brain" time) to initiate therapy within 60-90 min ("door-to-needle" time) after the patient has arrived at the emergency room or intensive care unit. This article reviews the current efforts to meet this goal (1) by implementing POCT of established biochemical markers such as cardiac troponins, creatine kinase MB, and myoglobin, in accelerated diagnosis and management workflow schemes, (2) by improving current POCT methods to obtain more accurate, more specific, and even faster tests through the integration of optical and electrochemical sensor technology, and (3) by identifying new markers for the very early and sensitive detection of myocardial ischemia and necrosis. Furthermore, the specific requirements for cardiac POCT in regard to analytical performance, comparability, and diagnostic sensitivity/specificity are discussed. For the future, the integration of new immunooptical and electrochemical chip technology might speed up diagnosis even further. However, every new development will have to meet the stringent method validation criteria set for corresponding central laboratory testing.

Biomarkers in Acute Coronary Syndrome

BACKGROUND: Evaluation of patients who present to the hospital with acute undifferentiated chest pain or other symptoms and signs suggestive of Acute Coronary Syndrome (ACS) is often a clinical challenge. The initial assessment, requiring a focused history (including risk factors analysis), a physical examination, an electrocardiogram (EKG) and serum cardiac marker determination, is time-consuming and troublesome. Recent investigations have indicated that increases in biomarkers of necrosis, inflammation, ischemia and myocardial stretch may provide earlier assessment of overall patient risk, help in identifying the adequate diagnostic and therapeutic management for each patient and allow for prevention of substantial numbers of new events. APPROACH AND CONTENT: The purpose of this review is to provide an overview of the characteristics of several biomarkers that may have potential clinical utility to identify ACS patients. Patho-physiology, analytical and clinical characteristics have been evaluated for each marker, underlying the properties for potential routine clinical use. SUMMARY: The biomarkers discussed in this review are promising and might lead to improved diagnosis and risk stratification of patients with ACS, however their clinical application requires further studies. It is important to define their clinical role as diagnostic markers, their predictive value and the specificity, standardization and detection limits of the assays.

New potential uses for cardiac troponins

This review briefly synthesizes the molecular biology of troponin, which is currently the best biochemical marker for the detection of cardiac injury and, thus, acute myocardial infarction as well. Potential new uses for the marker based on these insights, with a specific interest in cardiac troponin fragments that potentially could be linked to distinct clinical conditions, are described. Some of the clinical problems clinicians are faced with including how to use the markers in renal failure and the difficulties associated with the heterogeneity of current troponin assays are also discussed. Finally, we present the possibility of specific cardiac troponin fragments resulting from modification or degradation, associated with distinct pathological processes, as new potential uses for this biomarker.

Mechanism of troponin elevations in patients with acute ischemic stroke

Ischemic heart disease and cerebrovascular diseases frequently co-exist in the same patient, and similar risk factors are shared. For 60 years, experimental, observational, and clinical trial data have incessantly indicated that neurologically induced myocardial injury exists. Since the introduction of troponin in the diagnosis of acute myocardial infarction, this marker has been measured in a number of other conditions as well. One of these conditions is acute ischemic stroke, causing diagnostic dilemmas for clinicians. Because various electrocardiographic alterations have also been reported in these patients, it has been suggested that elevated troponin levels are somehow neurologically mediated, thus not caused by direct cardiac release. In conclusion, this review examines the available studies that systematically measured troponin in patients with acute ischemic stroke to properly interpret troponin elevations in these patients.

Evaluation of myocardial alterations using the enzymatic profile of elderly long-distance runners

Elderly population often is encouraged to practice sports in preventing cardiovascular diseases. However, evidences exist that intense physical efforts are related with a higher risk for acute myocardial infarction and sudden death. Biological markers for myocardial injury was analyzed in a group of 15 elderly athletes without a history of coronary artery disease, who participated in the 77th International Sao Silvestre race (15,000 m) in Sao Paulo City. A statistical difference was observed between total CPK activity levels before the run, immediately after the run, and some time later. Similar results were observed in the concentration of CK-MB mass. The cardiac troponin I (TnI-c) levels remained unchanged and within normal limits during the same time periods. The results of the present study showed no evidence of myocardial injury in elderly subjects without a history of coronary artery disease after participating in long-distance runs, as confirmed by the analysis of TnI-c levels. The increase in total CPK activity levels and the concentration of CK-MB mass do not represent myocardial injury in these subjects.

Cardiac markers and their point-of-care testing for diagnosis of acute myocardial infarction

Acute myocardial infarction (AMI) is the world's leading cause of mortality and morbidity. Therefore, quick and reliable diagnostics of AMI is extremely critical. Compared to the traditionally used central laboratory tests (CLT), which can be time-consuming and expensive, point-of-care testing (POCT) for AMI-indicative cardiac markers provides a convenient means for rapid diagnostic assays to be performed at the site of patient care delivery. In this article, the etiology and diagnosis of AMI are introduced, and some typical cardiac markers and their clinical applications are reviewed. Furthermore, the various POC cardiac marker devices that are currently available, the benefits of using cardiac marker POC assays, and challenges that cardiac marker POCT are facing are also discussed.

Biomarkers in acute cardiac disease: the present and the future

The use of biomarkers to aid diagnosis and treatment is increasing rapidly as genomics and proteomics help us expand the number of markers we can use and as an improved understanding of the pathophysiology of cardiac disease guides their use. However, as with all rapidly expanding fields, there is the risk of excessive enthusiasm unless we are circumspect about the data that guide the clinical use of these new tools. This review focuses first on how to use troponin, which at present is the best validated of the new markers, and will hopefully provide insight into how to use this biomarker more productively by distinguishing subsets of patients and by providing an understanding of the meaning of elevations in various clinical situations. The review then discusses the use as well as the knowledge gaps associated with emerging biomarkers such as B-type natriuretic peptide and C-reactive protein, which are increasingly moving toward more productive clinical use. Finally, it reflects on some of the large number of markers that are still in development.

The new definition of myocardial infarction and the impact of troponin determination on clinical practice

OBJECTIVE

To discuss the more controversial clinical and laboratory aspects in the application of the new biochemical diagnostic standard for myocardial infarction, 4 years after its introduction, and to make some suggestions, which could allow for a more realistic application of the new definition in the current clinical practice.

METHODS

Studies published in the last 4 years in the most important cardiology and laboratory medicine journals (including proceedings of the international meetings), discussing advantages and limits of the new definition of myocardial infarction, were reviewed and pertinent data were discussed and compared with similar information available in literature.

RESULTS AND CONCLUSIONS

Although the exact status of implementation of the new definition of myocardial infarction cannot yet be known, the trend toward such recommendation is evolving significantly, even if at different rates in different countries. To make the transition smoother, major educational efforts are required to disseminate the conceptual reasoning behind the new guidelines. On the other hand, more knowledge is needed for some relevant issues, such as the different analytical performance of cardiac troponin assays or the prognostic significance of biomarker changes after a percutaneous coronary intervention.

Cardiac markers in acute coronary syndrome

Over the last several years there has been a dramatic increase in the number of serum cardiac markers that may aid the diagnosis, prognosis, triage and treatment of patients with acute coronary syndrome. These markers help identify the degree of platelet activation, ischemia, inflammation, left ventricular dysfunction and myocardial necrosis encountered in acute coronary syndrome. The future challenge will be to determine which markers, or combination of markers, will be most effective in identifying and treating these patients.

Negative Interference in Cardiac Troponin I Immunoassays by Circulating Troponin Autoantibodies

Background: There are numerous potential sources of interference in immunoassays. Our aim was to identify the blood component that causes negative interference in cardiac troponin I (cTnI) immunoassays based on antibodies against the central part of cTnI.

Methods: We isolated an interfering factor (IF) from a sample with low recovery of added cTnI, using several consecutive purification steps: caprylic acid precipitation, ammonium sulfate precipitation, and purification on Cibacron Blue gel and protein G columns. Purified IF was identified by gel electrophoresis and mass spectrometric analysis of protein bands. For the direct detection of human antibodies to cardiac troponin in serum samples, we developed immunoassays using three different anti-human immunoglobulin antibodies and measured troponin antibodies in samples with low and normal cTnI recovery.

Results: Treatment with caprylic acid did not precipitate IF, but IF precipitated at 40% ammonium sulfate saturation. IF bound to a Cibacron Blue gel column, from which it was eluted with a linear salt gradient; it also bound to protein G. Gel electrophoresis of purified IF showed two major bands with molecular masses corresponding to the heavy (∼50 kDa) and light chains (∼25 kDa) of immunoglobulin, and their identities were confirmed by mass spectrometry. The presence of troponin-specific autoantibodies was confirmed in samples with low recoveries of cTnI by three different immunoassays. The median signals were significantly higher in 10 samples with low recovery than in 10 samples with normal recovery of cTnI (P ≤ 0.007).

Conclusions: Circulating autoantibodies to cTnI or other proteins of the troponin complex can be a source of negative interference in cTnI immunoassays.

Measurement of troponin I 48h after admission as a tool to rule out impaired left ventricular function in patients with a first myocardial infarction

Few studies have evaluated cardiac troponin I (cTnI) as a marker for infarct size and left ventricular (LV) dysfunction. Here we investigated the ability of a single-point cTnI, measured with a second-generation assay (Access AccuTnI), to estimate infarct size and assess LV function in patients with a first myocardial infarction (AMI). cTnI measurements were performed 12 and 48h after admission in 63 consecutive AMI patients. LV function was evaluated by gated single-photon emission computed tomography (SPECT) and infarct size was estimated by CK-MB peak and SPECT myocardial perfusion. LV function and infarct size were evaluated by SPECT before hospital discharge. SPECT was also repeated 3months later. Significant correlations (p<0.001) were found between cTnI at 12 and 48h and both the peak CK-MB (r=0.61 and r=0.82, respectively) and the perfusion defect size at SPECT (r=0.55 and r=0.61, respectively). cTnI at 12 and 48h were inversely related (p<0.001) to LV ejection fraction (LVEF) assessed both early (r=–0.45 and r=–0.57, respectively) and 3months after AMI (r=–0.51 and r=–0.69, respectively). cTnI >14.8 μg/L at 48h predicted an LVEF <40% at 3months with a sensitivity of 100% [95% confidence interval (CI) 73.5–100%], specificity of 65% (CI 49–79%), and a negative predictive value of 100%. Our findings demonstrate that a single cTnI measurement 48h after admission is useful for ruling out impaired LV function in a routine clinical setting.

The incremental value of troponin-I testing in patients with intermediate risk unstable angina

BACKGROUND

Classification of patients with unstable angina (UA) by Agency for Health Care Policy and Research (AHCPR) guidelines in the emergency department reliably stratifies risk of death or myocardial infarction (MI) for triage to outpatient evaluation (low-risk), hospitalization (high-risk), or additional testing (intermediate-risk). Cardiac troponin-I elevation may identify patients at higher risk, but the incremental value may vary with AHCPR clinical risk.

HYPOTHESIS

The objective of this study was to determine whether cardiac troponin-I had any additional value beyond triage based upon history, physical examination, and electrocardiogram, in the evaluation of patients with UA.

METHODS

In all, 212 consecutive patients with UA and normal serum creatine kinase (CK)-MB levels and elevated troponin-I were risk stratified by AHCPR guidelines to evaluate the incremental value of adding routine troponin-I measurements to our current model for risk stratification.

RESULTS

Primary events (death/nonfatal MI) occurred in 35% of high-risk, 15% of intermediate-risk, and 0% of low-risk patients (p < 0.001 by chi-square for trend). High troponin-I (> or =2.0 ng/dl) occurred in 48% of high-risk, 21% of intermediate-risk, and 19% of low-risk patients. The remaining patients in each risk group had indeterminate troponin-I levels (> or =0.4 < 2 ng/dl). Of those with high troponin-I, a primary event occurred in 36, 42, and 0% in the respective high-, intermediate-, and low-risk groups (p < 0.001). High troponin-I levels corresponded with a statistically significant increased rate of primary events only in patients at AHCPR intermediate risk: 42.4 vs. 7.3%, p < 0.001.

CONCLUSION

The AHCPR guidelines risk stratify patients with UA. High troponin-I adds significant (p < 0.001) prognostic value in the patients at AHCPR intermediate risk and should be evaluated further in larger trials of such patients.

Role of cardiac troponin testing in percutaneous transluminal coronary angioplasty

Percutaneous transluminal coronary angioplasty (PTCA) is a common invasive procedure for myocardial revascularization. This article reviews the role of monitoring cardiac troponins in identifying procedural myocardial damage as a result of PTCA, its associations with balloon inflation time, stenting, side-branch occlusion and the prognostic implications of elevated levels of cardiac troponins. A review of several studies demonstrates that cardiac troponins are more sensitive than creatine kinase MB, CK-MB (mass) in detecting minor myocardial damage during PTCA. Increases in post-procedural cardiac troponin T and cardiac troponin I are associated with a greater degree of morbidity and mortality. Increases are more common and more pronounced following a longer duration of balloon inflation time, stenting and side-branch occlusion. Elevated cardiac troponins pre-procedure are a poor prognostic indicator.

Current concepts in standardization of cardiac marker immunoassays

Cardiac markers are measured by a number of different immunoassays using specific antibodies directed to the respective antigens. Lacking assay standardization, different results from different assays measuring the same marker may be obtained and this problem may cloud interpretations of reported data. Presently, there are no reference procedures for cardiac markers; certified reference materials should still be established and, at least for cardiac troponins, the analyte in the patients' blood is significantly different from newly synthesized protein. It is therefore clear that the problems of cardiac marker standardization will not be quickly solved. A number of projects are, however, underway under the auspices of the IFCC and other organizations. The aim of this opinion is to reflect on some concepts related to the implementation of a metrologically correct measurement system, giving practical examples on how these concepts can be applied to immunoassays measuring cardiac markers.

Comparison of cardiac troponin T and I in healthy men and in aortic valve replacement

Troponins are of outstanding importance for the diagnosis of myocardial infarction. Cardiac troponin T (cTnT) and the various cardiac troponin I (cTnI) assays differ with respect to method comparison, diagnostic sensitivity and diagnostic specificity. To understand the differences in the diagnostic behavior of troponin assays, AccuTnI and Elecsys Troponin STAT were used in a group of healthy men and in the follow-up of patients with aortic valve replacement (AVR). Within the healthy subjects AccuTnI was able to differentiate two subgroups from each other, whereas the cTnT concentrations of all subjects were below the detection limit. In AVR patients, cTnT and cTnI correlated sufficiently, if the postoperative periods were taken into consideration. There was a rapid increase in cTnI within 24 h. In contrast, a broad peak was evident for cTnT between 48 and 120 h. The results emphasize more the differences in the release of cTnI and cTnT from the cytoplasm and the thin filaments of the cardiomyocytes than the modifications of the troponins circulating in the blood.

Cardiac troponin T and I and creatine kinase-MB as markers of myocardial injury and predictors of outcome following percutaneous coronary intervention

AIMS

This study was performed to determine the most sensitive biochemical marker for the detection of cardiac myocyte damage potentially sustained during percutaneous coronary intervention (PCI) and to assess whether such a marker can be used to identify patients at increased risk of poor subsequent clinical outcome.

METHODS AND RESULTS

We studied 109 consecutive patients presenting with clinical stable and unstable angina and undergoing PCI at our institution. Blood was sampled for creatine kinase-MB (CK-MB), cardiac Troponin T (cTnT) and I (cTnI) immediately before and at 6, 14 and 24 h post-PCI. Five patients with raised cardiac markers pre-PCI were excluded from further analysis. The occurrence of major adverse cardiac events (MACE) was documented in-hospital, at 30 days and at long-term clinical follow up of up to 20 months. MACE occurred in 26/109 (24%) patients: death=1, QWMI=4, NQWMI=5, repeat PCI=16 (nine target vessel revascularisations and seven de-novo lesions), CABG=5. cTnI had the highest detection rate for myocardial damage, with 58 cTnI-positive patients, 38 cTnT-positive patients and 28 CK-MB-positive patients in the 24 h following PCI (Pearson's Chi square test, P<0.01). The type of interventional strategy per se was not significantly associated with post-procedural cardiac marker concentrations (Kruskal-Wallis ANOVA, P>0.05). There was a significant association between post-procedural cardiac marker concentrations of CK-MB, cTnT and cTnI and the occurrence of procedural angiographic complications (P=0.0003, 0.0002, 0.001, respectively). All three markers, at each sampling time point between 6 and 24 h post-PCI, showed a significant predictive relationship with MACE in-hospital and at long-term follow up (ROC curve AUC analysis, P<0.05). All three markers provided equally predictive information at each of the three post-procedural sampling time points between 6 and 24 h following PCI. All levels of cardiac marker elevation above the clinically discriminant cut-off values were significantly predictive of outcome at long-term follow up.

CONCLUSIONS

cTnI proved to be the most sensitive marker in detecting myocardial necrosis following PCI. CK-MB, cTnT and cTnI all provided similarly reliable prognostic information, with cTnT and cTnI being marginally superior in predicting MACE at follow up.

Negative interference in cardiac troponin I immunoassays from a frequently occurring serum and plasma component

BACKGROUND

Cardiac troponin I (cTnI) is a sensitive marker of cardiac injury, but cTnI assays, like other immunoassays, are susceptible to interferences. We evaluated the presence of interfering substances by measuring the recovery of cTnI added to samples from volunteers and from patients with acute coronary syndromes (ACS).

METHODS

We added a ternary complex of human cardiac troponin (30-500 microg/L) or cTnI from serum to samples from healthy volunteers and ACS patients. We measured cTnI with a two-site sandwich time-resolved immunofluorometric assay using two antibodies against epitopes in the central stable part of cTnI. We also analyzed 108 heparin-plasma samples from 16 ACS patients with this assay, with an assay based on four antibodies, and with two commercial cTnI assays, AxSYM and ACS:180.

RESULTS

In samples from both healthy persons and ACS patients, recoveries for our assay were 1-167% (range). Recoveries were increased by addition of an antibody with an epitope in the N-terminal region of cTnI to the solid phase and an antibody with an epitope in the C-terminal region as a second detection antibody. In 2 of 16 patients with ACS, normal cTnI concentrations found when measured with the original assay demonstrated clinically abnormal (up to 10-fold higher) results with the additional N- and C-terminal antibodies in the early phase of infarction. Both commercial cTnI assays also demonstrated clinically misleading, falsely low cTnI concentrations.

CONCLUSIONS

Some yet unidentified, variable component, present in the blood from healthy volunteers and ACS patients, interferes with the binding of antibodies against epitopes in the central part of cTnI used in two commercial assays. Our approach to supplement the mid-fragment cTnI antibodies with antibodies in the N- and C-terminal parts of the molecule in an experimental assay represents a step in resolving this interferent.

Acute coronary syndrome: biochemical strategies in the troponin era

New biomarkers, such as cardiac troponins, have a major role to play for cost-effective management of individuals with acute chest pain and suspected coronary syndrome, and the laboratory is now poised to assume a vital role in assessing damage and determining prognosis. The redefined biochemical criterion proposed to classify acute coronary syndrome patients presenting with ischemic symptoms as patients with myocardial infarction is heavily predicated on an increased troponin concentration in blood. In an era of evidence-based medicine, we can no longer overlook the diagnostic and prognostic benefits provided by the measurement of these highly sensitive and specific proteins.

The measurement of cardiac markers: where should we focus?

Cardiac markers are presently a hot topic, with active debate on their use. They now have a major role for cost-effective management of acute chest pain and suspected acute coronary syndrome. The laboratory has a pivotal role in proper selection and interpretation of available markers, depending on the creation of evidence-based knowledge about test utilization and sources of variation. This article reviews this knowledge in the field of biomarkers determination and summarizes the major analytic and clinical issues, with reference to various recent recommendations of laboratory medicine and cardiology expert groups.

Cardiac troponin I for risk stratification following percutaneous coronary artery intervention in acute coronary syndromes

The cardiac troponins have been shown to provide prognostic information allowing risk stratification of patients with acute coronary syndromes (ACS). The benefit of early percutaneous coronary intervention (PCI) in this setting has been highlighted by the FRISC II study. We assessed the pattern of release of cardiac troponin I (cTnI) following PCI in patients with ACS and evaluated its prognostic value for major adverse cardiac events (MACE): death, Q-wave myocardial infarction (QWMI), and repeat revascularization at follow-up. cTnI was sampled at baseline and 6, 14, and 24 hr following PCI in 73 patients presenting with unstable and post-MI angina. Clinical follow-up was obtained in all 73 patients at a mean period of 43 +/- 19.9 weeks (range, 11-68 weeks). Patients were stratified into two groups according to whether cTnI remained unchanged or fell below baseline 24 hr post-PCI (group 1, n = 47) or increased above baseline 24 hr following PCI (group 2, n = 26). MACE occurred in 4 (8.5%) of patients in group 1 (QWMI = 1, CABG = 1, re-PCI = 2) and in 19 (73%) of patients in group 2 (death = 1, QWMI = 2, CABG = 2, re-PCI = 14; chi-square = 32.34, P < 0.0001). The positive predictive value of rising cTnI within 24 hr following PCI for MACE at follow-up was 0.73 and the negative predictive value was 0.92 (specificity = 83%, sensitivity = 86%; odds ratio = 29.18, 95% CI = 7.62-110.64, P < 0.0001). cTnI is an inexpensive and widely applicable tool that offers reliable prognostic information for the risk stratification of patients undergoing coronary revascularization in the setting of acute coronary syndromes and may identify a group of patients at particular risk of repeat PCI.

Recent approaches in standardization of cardiac markers

The development of commercial assays for the determination of new cardiac proteins has been one of the most important innovations in the field of cardiovascular diagnostics in the last decade. This significant and sudden advancement has however led to some analytical and interpretative problems. There are problems in test standardization, imprecision, interference and preanalytical variability. We also need to standardize utilization of biomarkers in diagnosis and management of acute cardiac syndromes and clearly define decision thresholds. Powerful tests, such as cardiac markers, on which critical decisions will rest, need highly reliable methods. The feeling is that some assays are inadequately appraised prior to their introduction in clinical use. More studies are needed to implement new devices in the laboratory routine, and only well documented assays should be used in hospital-based laboratories. The technology to address many analytic problems is at hand, but commitment on the part of manufacturers and their customers in the laboratory community is essential.

Clinical significance of low-positive troponin I by AxSYM and ACS:180

We compared troponin I (TnI) assays (AxSYM [Abbott]; ACS:180 [Bayer]) in blood samples with concentrations less than 10 ng/mL (< 10 micrograms/L). Discordant results were evaluated by linearity studies and by testing for rheumatoid factor. Patients with discordant TnI results were compared with patients with concordant results and patients with negative TnI who had a new myocardial infarction or died within 2 months of initial testing. Positive TnI cutoffs by AxSYM and ACS:180 were 0.7 ng/mL (0.7 microgram/L) and 0.13 ng/mL (0.13 microgram/L), respectively. We identified 173 specimens that were repeatedly positive by at least 1 assay; 143 specimens were positive by both assays. Twenty samples positive for TnI by AxSYM were negative by ACS:180, while 10 samples positive by ACS:180 were negative by AxSYM. The discordant samples showed no evidence of interfering substances, including rheumatoid factor. Clinical follow-up showed that 26% of patients with elevated TnI by both assays, 33% with TnI positive only by AxSYM, 22% with TnI positive only by ACS:180, and 8% with negative TnI by AxSYM encountered at least 1 clinical end point. Variable detection rates by these assays for low-positive TnI represent a clinically significant problem.

Clinical evaluation of the ACS:180 cardiac troponin I assay

All patients admitted to the coronary care unit with suspected acute coronary syndromes were evaluated by serial electrocardiography and blood draws on admission and at 4 and 12h from admission. Diagnosis was based on conventional WHO criteria. Samples were measured for creatine kinase (CK), cardiac troponin T (cTnT), myoglobin, CK isoenzyme MB (CK-MB) and cardiac troponin I (cTnI). A set of samples from individuals undergoing extreme endurance training was also examined. Analytical imprecision was consistent with published quality goals. Samples were stable for cTnI under a range of storage conditions, including multiple freeze thaw cycles. CK-MB, cTnI and cTnT were equally efficient for the diagnosis of acute myocardial infarction, irrespective of the final diagnostic criteria used. Both cTnI and cTnT were of equal efficiency in the identification of a high-risk subgroup of patients with unstable angina. Significant elevations of cTnI were not seen in an e ndurance-training group.

Measurement of cardiac troponins

The cardiac troponins form part of the regulatory mechanism for muscle contraction. Specific cardiac isoforms of cardiac troponin T and cardiac troponin I exist and commercially available immunoassay systems have been developed for their measurement. A large number of clinical and analytical studies have been performed and the measurement of cardiac troponins is now considered the 'gold standard' biochemical test for diagnosis of myocardial damage. There have been advances in understanding the development and structure of troponins and their degradation following myocardial cell necrosis. This has contributed to the understanding of the problems with current assays. Greater clinical use has also highlighted areas of analytical and clinical confusion. The assays are reviewed based on manufacturers' information, current published material as well as the authors' in-house experience.

Comparison of diagnostic performance of cardiac troponin I on the IMMULITE system with other automated troponin I assays in minor myocardial damage

An analytical and clinical evaluation of cardiac troponin I (cTnI) on the IMMULITE system is presented. The assay results were compared with those of the Stratus II and the Dimension RxL-HM. A between-run imprecision CV < 20% was found at a cTnI concentration of 0.23 microg/L (functional limit of detection). On the basis of a reference study including 215 patients without ischemic heart disease (97.5th percentile: 0.294 microg/L) and 36 patients clinically classified as having stable angina pectoris (<0.22 microg/L) a preliminary cutoff level of 0.3 microg/L was defined. Assay linearity, sample stability, influence of sample material and method comparison studies were performed. In patients with Duchenne's disease, chronic hemodialysis treatment, pulmonary embolism, coronary artery bypass surgery and minimally cardiac surgery the cTnI results of the IMMULITE agreed better with the Dimension RxL-HM than with the Stratus II data. Of 142 samples from patients with unstable angina 67 samples were classified as cTnI positive with the IMMULITE, 76 with the Dimension RxL-HM, and 62 with the Stratus II. In conclusion, the new assay is sensitive for the determination of cTnI and easy to perform within 45 min.

Membrane assisted isoform immunoassay. A rapid method for the separation and determination of protein isoforms in an integrated immunoassay

Proteins often exist as isoforms with structural microheterogenity due to, for example, small variations in their carbohydrate structure. This can give rise to differences in biological activity. Measurements of low concentrations of such isoforms are usually performed by complicated methods, which demand discrete steps of separation (chromatographic or electrophoretic) and immunodetection. In this paper a new, highly specific and rapid (<15 min) analytical technique is described which permits the quantitative determination of several types of protein isoform. The method, which is called membrane assisted isoform immunoassay (MAIIA), is based on separation (by ion-exchange or affinity chromatography) and immunoassay detection of the protein isoforms in the same lateral flow, assisted by capillary forces in a membrane device. The technique is exemplified with a method for measuring carbohydrate-deficient isoforms of the glycoprotein transferrin, where the measured isoforms constitute a minimal part (<3%) of the total amount of transferrin. The time for the measurement was about 10 min and the correlation coefficient with an established, commercial two-step procedure, which takes 4-5 h to perform, was 0. 99. The detection limit was about 1 fmol of transferrin. The anion-exchange membrane used in the test device had the ability to separate transferrin isoforms with down to 0.1 unit difference in pI. The results indicate that the technique should be useful for rapid point-of-care testing of clinically interesting charged protein isoforms.

Cardiac troponin I for stratification of early outcomes and the efficacy of enoxaparin in unstable angina: a TIMI-11B substudy

OBJECTIVES

We sought to evaluate cardiac troponin I (cTnI) for predicting early clinical outcomes and the efficacy of enoxaparin among patients with non-ST segment elevation acute coronary syndrome (ACS) and negative creatine kinase, MB fraction (CK-MB) levels.

BACKGROUND

Cardiac TnI identifies patients with unstable angina who are at higher risk of death or myocardial infarction (MI) by 30 days. The utility of cTnI for predicting very early clinical events, including recurrent ischemia, and the efficacy of enoxaparin are not yet established.

METHODS

At baseline and 12 h to 24 h after enrollment in the Thrombolysis in Myocardial Infarction (TIMI)-11B trial, samples were collected for cTnI determination.

RESULTS

Among 359 patients with negative serial CK-MB values, 50.1% had a cTnI result > or =0.1 ng/ml within the first 24 h. Patients with elevated cTnI were at higher risk of death or MI at 48 h (3.9 vs. 0%, p = 0.01) and 14 days (13.9 vs. 2.2%, p<0.0001). Elevated cTnI also correlated with higher risk of recurrent ischemia requiring urgent revascularization by 48 h (10.0 vs. 1.7%, p = 0.001) and 14 days (20.6 vs. 5.6%, p< or =0.0001). Enoxaparin had a greater benefit among patients with elevated vs. normal cTnI (p = 0.03), achieving a 47% reduction in the risk of death, MI or urgent revascularization by 14 days in cTnI-positive patients (p = 0.007).

CONCLUSIONS

Elevation of cTnI among patients with non-ST segment elevation ACS and negative levels of CK-MB identifies those at higher risk for very early adverse outcomes, including severe recurrent ischemia. Treatment with enoxaparin reduces the risk associated with elevated cTnI.