Laboratory-related issues in the measurement of cardiac troponins with highly sensitive assays

A number of assay-related issues can affect the performance of cardiac troponin (cTn) measurement in everyday practice. In this respect, it is vital that all information on cTn assays is known and that the performance characteristics of assays are objectively assessed and adequately described. The advent of the latest generation of more sensitive cTn assays has heralded a new wave of information about low concentrations of cTn in blood. These recent generation assays have improved analytical sensitivity and corresponding performance at low cTn concentrations when compared to their predecessors, providing a convincing goal for laboratory medicine in helping clinicians in the diagnosis of acute myocardial infarction. Crucial to the clinical utility of highly sensitive cTn assays is the laboratorians' role in closely scrutinizing proposed assays and defining their value in relation to available evidence. Analytical, as well as pre-analytical and post-analytical, aspects must be documented. In this review, we describe what laboratory professionals should know about their cTn assay performance characteristics and the pre-analytical prerequisites for robustness to ensure optimal post-analytical reporting.

Reference limits of high-sensitive cardiac troponin T indirectly estimated by a new approach applying data mining. A special example for measurands with a relatively high percentage of values at or below the detection limit

A new model for the indirect estimation of reference limits (RLs) has been proposed recently and was coined TMC approach (truncated minimum chi-square estimation) which can be performed with R statistic. A spline function is applied to the RLs to get a continuous function if age is graphically presented vs. the RLs avoiding artificial “jumps” between different age groups. Most indirect models assume a power normal distribution and fail if this assumption is not fulfilled as e.g. if a relatively high percentage of measured values is below the detection limit and the data are distributed extremely skewed. This problem is handled by the TMC model. High-sensitive cardiac troponin T (hs cTnT) was chosen as an example. The hs cTnT concentration in serum or plasma is well accepted as a valuable marker in the diagnosis of acute myocardial infarction. Currently, the 99th percentile derived from a “healthy” subpopulation is the decision limit recommended by consensus groups. However, this decision limit is questioned by several authors for many reasons. In the present report, the 97.5th and the 99th percentile limits were reinvestigated by the TMC model with different subpopulations stratified according to age and sex and were finally compared to presently recommended decision limits. In summary, the generally recommended 99th percentile as a fixed decision limit should be reconsidered. It is suggested to apply more specific reference limits stratified for age and sex instead of a fixed decision limit.

Clinical Determinants of Myocardial Injury, Detectable and Serial Troponin Levels among Patients with Hypertensive Crisis

Introduction There is a high prevalence of hypertensive crisis with myocardial injury, as evidenced by elevation in cardiac troponin levels. The risk factors predisposing patients to developing a myocardial injury, detectable troponin, and increase in serial troponin in this population are not known. Methods A retrospective study was designed to include all patients, presenting to the emergency room, diagnosed with hypertensive crisis, using International Classification of Diseases, 10th revision, Clinical Modification (ICD-10-CM) codes between 2016-2018 (n=467). Logistic regression was used to determine the important predictors of myocardial injury evidenced by troponin elevation >99th percentile of upper reference level (URL), detectable troponin (> 0.015 ng/ml), and increase in serial troponin levels. Results The 99th percentile of the initial troponin level among all patients was 0.433 ng/ml. A total of 15% had a myocardial injury, and the significant risk factors associated with it were body mass index (BMI) < 30 kg/m2 (odds ratio [OR] 0.50, confidence interval [CI] 0.28-0.89), congestive heart failure (CHF; OR 4.28, CI 2.21-8.25) and prior use of aspirin (OR 1.98, CI 1.08-3.63). About 35% had detectable troponin, and BMI < 30 kg/m2 (OR 0.62, CI 0.40-0.97), CHF (OR 3.49, CI 2.06-5.9), elevated creatinine (OR 1.17, CI 1.02-1.34) and age <61 years (OR 0.59, CI 0.38-0.94) were associated with it. The factors associated with an increase in serial troponin were BMI < 30 Kg/m2 (OR 0.56, CI 0.36-0.87), CHF (OR 1.78, CI 1.06-3.0), coronary artery disease (CAD; OR 2.08, CI 1.28-3.36) and non-Caucasian race (OR 0.52, CI 0.29-0.93). Conclusion About one-third of patients with the hypertensive crisis have detectable troponin. Still, among these, less than half have troponin levels >99th percentile URL, and the majority of these patients have minimal changes in serial troponin. Low BMI was associated with higher initial and serial troponin levels, and this obesity paradox was stronger among females and older patients.

Analytical validation of cardiac troponin I assays in horses

Human cardiac troponin I (cTnI) assays have been used in equine medicine, often without prior analytical validation for equine use. In the absence of appropriate validation, the clinical significance of assay results is uncertain and can lead to misdiagnosis. We followed the American Society for Veterinary Clinical Pathology guidelines and investigated linearity, precision, limit of quantification (LoQ), and comparative recovery for 6 commercial cTnI assays developed for use in human medicine. Clinically acceptable linearity was observed in assays A-D, whereas assay E did not detect equine cTnI in any sample. Comparative recovery revealed 1-3-fold differences between assay results, and low analyte recoveries (2.2-3.4%) were observed in assay F. Precision was investigated in assays A and B, and found to be within acceptable limits. The LoQ was 1.53 ng/L for assay A, and 0.031 µg/L for assay B. Assays A and B performed within clinically acceptable limits and were deemed suitable for use in equine medicine. Assays C and D did not undergo full validation but had acceptable linearity, which demonstrates their potential for use in equine medicine. Assays E and F are unsuitable for use in horses given issues with detection of equine cTnI. The variability in results between assays indicates that reference intervals and cutoffs for diagnostic decision-making are assay specific and should be established prior to adoption by diagnostic laboratories.

Advances in Cardiac Biomarkers of Acute Coronary Syndrome

Acute coronary syndrome (ACS) encompasses a pathophysiological spectrum of cardiovascular diseases, all of which have significant morbidity and mortality. ACS was once considered an acute condition; however, new treatment strategies and improvements in biomarker assays have led to ACS being an acute and chronic disease. Cardiac troponin is the preferred biomarker for the diagnosis of myocardial infarction, and there is considerable interest and efforts toward development and implementation of high-sensitivity cardiac troponin (hs-cTn) assays worldwide. Analytical and clinical performance characteristics of hs-cTn assays as well as testing limitations are important for laboratorians and clinicians to understand in order to utilize testing appropriately. Furthermore, expanding the clinical utility of hs-cTn into other cohorts such as asymptomatic community dwelling populations, heart failure, and chronic kidney disease populations supports novel opportunities for improved short- and long-term prognosis.

Troponin assays in the assessment of the equine myocardium

In 2000, troponin assays were adopted as the test of choice for detection of myocardial injury in man. This decision was made after extensive testing and followed a 60 year search for a biomarker of myocardial damage with sufficient analytical sensitivity and specificity. This has led to proliferation of assays for use in human medicine, each requiring extensive testing and validation before it could be made available on the open market for human use. The search for ever-more analytically sensitive assays and for a standard reference material continues. The adoption of troponin testing in veterinary medicine followed shortly after its development for use in man, providing a much-needed means of detecting and monitoring myocardial damage in horses. However, application of these tests in veterinary medicine has exclusively involved use of assays designed for and clinically validated in human patients. There is no mandated requirement for test validation in veterinary medicine and, while many of these assays have been shown to be capable of detecting equine troponin, the wide diversity of available tests, lack of validation, absence of protocols for their use and lack of standardisation make their application problematic. The objective of this review article is to address this issue, offering guidance where data are available and encouraging caution where there are none. Ultimately, the overall goal of this review is to examine critically the use of troponin assays in the horse and to promote the accurate and appropriate interpretation of valid results.

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.

Delta troponin for the early diagnosis of AMI in emergency patients with chest pain

OBJECTIVES

In patients presenting to the Emergency Department (ED) with potential acute myocardial infarction (AMI), elevated cardiac troponin (cTn) levels are indicative of myocardial necrosis. We assessed the accuracy of 'delta cTn' at 2h or 6h compared to the cTn concentration above the 99th percentile reference value for AMI in a prospective study of adult patients presenting to ED with symptoms suggestive of possible acute coronary syndrome.

METHODS

Blood was sampled for cardiac troponin I (cTnI) on presentation, and at 2h and 6h following presentation using a sensitive assay (Beckman AccuTnI). All clinical endpoints were adjudicated by a cardiologist who was blinded to the 2h cTn assay result.

RESULTS

Of the 874 patients, 70 (8%) were diagnosed with an AMI during their index presentation. The area under the ROC curve for diagnosing AMI at 2h was 0.89 [95%CI, 0.84-0.95] for absolute delta cTn versus 0.79 [95%CI 0.73-0.85] for the relative change. Specificity and PPV at 2h were optimized using a delta cTnI ≥ 0.03 μg/L (95.8% [95%CI 94.1-97.0] and 61.4% [95%CI 50.9-70.9] respectively). Sensitivity and NPV for AMI were optimized using the 99th percentile with the addition of a delta of<0.03 μg/L (97.1% [95%CI 90.2-99.2] and 99.7% [95%CI 99-99.9] respectively).

CONCLUSIONS

An algorithm incorporating cTnI concentration and delta cTn values with a sensitive troponin assay allows accurate diagnosis of AMI within 2h from presentation and earlier rule-out of AMI in the majority of patients.

High-sensitivity troponin T as a marker of myocardial injury after radiofrequency catheter ablation

Background

The aim of our study was to monitor radiofrequency catheter ablation-induced myocardial damage by measuring high-sensitivity cardiac troponin T (hs-cTnT).

Methods

Serum concentrations of hs-cTnT (Elecsys 2010 system, Roche) were measured in 73 healthy blood donors and serially in 27 patients who had samples taken both before and 24 h after radiofrequency ablation (RFA) for atrioventricular nodal re-entry tachycardia (AVNRT), atrial fibrillation (AF) or right atrial flutter (AFL).

Results

Significant increases of hs-cTnT were seen in patients after RFA (AVNRT: P = 0.0115, AF: P = 0.0011, AFL: P = 0.0009). Postprocedural serum hs-cTnT correlated with the number of radiofrequency applications and with the duration of RFA procedure. Spearman's coefficient of rank correlation ( r) were as follows: hs-cTnT versus RFA duration: r = 0.771 ( P < 0.001); hs-cTnT versus number of pulses: r = 0.708 ( P < 0.001). Patients with the diagnosis of AVNRT had lower serum hs-cTnT concentration after RFA compared with AFL ( P < 0.0001) and AF ( P < 0.0001) patients.

Conclusions

Our data indicate that RFA causes a significant increase of serum hs-cTnT concentration that could be used to monitor myocardial injury.

Recommendations for the use of cardiac troponin measurement in acute cardiac care

The release of cardiomyocyte components, i.e. biomarkers, into the bloodstream in higher than usual quantities indicates an ongoing pathological process. Thus, detection of elevated concentrations of cardiac biomarkers in blood is a sign of cardiac injury which could be due to supply-demand imbalance, toxic effects, or haemodynamic stress. It is up to the clinician to determine the most probable aetiology, the proper therapeutic measures, and the subsequent risk implied by the process. For this reason, the measurement of biomarkers always must be applied in relation to the clinical context and never in isolation. There are a large number of cardiac biomarkers, but they can be subdivided into four broad categories, those related to necrosis, inflammation, haemodynamic stress, and/or thrombosis. Their usefulness is dependent on the accuracy and reproducibility of the measurements, the discriminatory limits separating pathology from physiology, and their sensitivity and specificity for specific organ damage and/or disease processes. In recent years, cardiac biomarkers have become important adjuncts to the delivery of acute cardiac care. Therefore, the Working Group on Acute Cardiac Care of the European Society of Cardiology established a committee to deal with ongoing and newly developing issues related to cardiac biomarkers. The intention of the group is to outline the principles for the application of various biomarkers by clinicians in the setting of acute cardiac care in a series of expert consensus documents. The first of these will focus on cardiac troponin, a pivotal marker of cardiac injury/necrosis.

Use of a nurse-led intervention to optimize beta-blockade for reducing cardiac events after major noncardiac surgery

BACKGROUND

Although guidelines recommend the use of beta-adrenoceptor blocking drugs to reduce cardiac events (CEs) after major noncardiac surgery, trial results have varied between showing benefit, ineffectiveness, and harm. We sought whether optimizing beta-blockade (BB) delivery could make them more effective.

METHODS

Intermediate risk patients undergoing major noncardiac surgery (n = 400) were randomized to 2 strategies of BB therapy: universal BB (UBB; n = 197) comprising an algorithm-based, nurse-led strategy to optimize dosing and adherence to bisoprolol titration over > or =1 week preoperatively versus usual care (UC; n = 203), whereby BB are continued in those already taking them or prescribed for patients identified as high risk based on ischemia (new or inducible wall motion abnormalities) at dobutamine echocardiography (DbE). Daily electrocardiogram and troponin levels were obtained on 3 postoperative days. The primary end point was a major CE (cardiac death or myocardial infarction) within 30 days.

RESULTS

There were 25 major CEs (6.3%), occurring in 13 (6.6%) of 197 UBB and 12 (5.9%) of 203 UC patients (OR 1.12, 95% CI 0.52-2.39). Independent predictors of CEs were baseline systolic blood pressure (beta 1.02, P = .005) and postoperative hypotension (beta 1.02, P = .03) but not treatment strategy. Those randomized to UBB had significantly better heart rate control perioperatively, at the cost of bradycardia and hypotension. The negative predictive value of DbE in this study was 95%.

CONCLUSIONS

These data confirm a persistent CE rate after major noncardiac surgery despite nurse-led dose titration of bisoprolol. Cardiac events were equivalent to a UC strategy based on DbE results.

Reference population and marathon runner sera assessed by highly sensitive cardiac troponin T and commercial cardiac troponin T and I assays

BACKGROUND

Endurance exercise can increase cardiac troponin (cTn) concentrations as high as those seen in cases of minor myocardial infarction. The inability of most cTn assays to reliably quantify cTn at very low concentrations complicates a thorough data analysis, and the clinical implications of such increases remain unclear. The application of recently developed highly sensitive cTn immunoassays may help resolve these problems.

METHODS

We evaluated the precommercial highly sensitive cardiac troponin T (hs-cTnT) assay from Roche Diagnostics and the Architect cardiac troponin I (cTnI-Architect) assay from Abbott Diagnostics by testing samples from a reference population of 546 individuals and a cohort of 85 marathon runners. We also measured the samples with the current commercial cTnT assay for comparison.

RESULTS

Although the hs-cTnT and cTnI-Architect assays were capable of measuring cTn concentrations at low concentrations (<0.01 microg/L), only the hs-cTnT assay demonstrated a CV of <10% at the 99th percentile of the reference population and a near-gaussian distribution of the measurements. After a marathon, 86% of the runners had cTnT concentrations greater than the 99th percentile with the hs-cTnT assay, whereas only 45% of the runners showed increased concentrations with the current cTnT assay. cTn concentrations remained significantly increased the day after the marathon. A multiple regression analysis demonstrated marathon experience and age to be significant predictors of postmarathon cTn concentrations (P < 0.05).

CONCLUSIONS

The hs-cTnT assay was the only assay tested with a performance capability sufficient to detect cTn concentrations in healthy individuals. The number of runners with increased cTn concentrations after a marathon depends highly on an assay's limit of detection (LOD). The assay with the lowest LOD, the hs-cTnT assay, showed that almost all runners had increased cTn concentrations. The clinical implications of these findings require further investigation.