Specificity of a High-Sensitivity Cardiac Troponin I Assay Using Single-Molecule–Counting Technology

The Challenges of Developing Biosensors for Clinical Assessment: A Review

Emerging research in biosensors has attracted much attention worldwide, particularly in response to the recent pandemic outbreak of coronavirus disease 2019 (COVID-19). Nevertheless, initiating research in biosensing applied to the diagnosis of diseases is still challenging for researchers, be it in the preferences of biosensor platforms, selection of biomarkers, detection strategies, or other aspects (e.g., cutoff values) to fulfill the clinical purpose. There are two sides to the development of a diagnostic tool: the biosensor development side and the clinical side. From the development side, the research engineers seek the typical characteristics of a biosensor: sensitivity, selectivity, linearity, stability, and reproducibility. On the other side are the physicians that expect a diagnostic tool that provides fast acquisition of patient information to obtain an early diagnosis or an efficient patient stratification, which consequently allows for making assertive and efficient clinical decisions. The development of diagnostic devices always involves assay developer researchers working as pivots to bridge both sides whose role is to find detection strategies suitable to the clinical needs by understanding (1) the intended use of the technology and its basic principle and (2) the preferable type of test: qualitative or quantitative, sample matrix challenges, biomarker(s) threshold (cutoff value), and if the system requires a mono- or multiplex assay format. This review highlights the challenges for the development of biosensors for clinical assessment and its broad application in multidisciplinary fields. This review paper highlights the following biosensor technologies: magnetoresistive (MR)-based, transistor-based, quartz crystal microbalance (QCM), and optical-based biosensors. Its working mechanisms are discussed with their pros and cons. The article also gives an overview of the most critical parameters that are optimized by developing a diagnostic tool.

High sensitivity troponins and conventional troponins at the bedside

The continuing advances in the biochemical research for the discovering an ideal biomarker for diagnosing myocardial injury have led to discovery cardiac Troponin, a biochemical gold standard for myocardial necrosis. Further with advances in the immunoassay techniques, the 99th percentile cutoff value of cardiac troponin required for the diagnosis of myocardial infarction decreased, with the latest available ultrasensitive cardiac troponin assay capable of measuring level as low as 0.005 ng/ml. Troponin have both diagnostic as well as prognostic significance in myocardial necrosis, but the cut off value by 99th percentile rule is useful only when applied to patients with a high pretest probability of Acute Coronary Syndrome(ACS) and also the results must be interpreted in the context of clinical history, ECG findings, and possibly cardiac imaging to establish the correct diagnosis. As cardiac troponins are also elevated in other cardiac conditions such as cardiomyopaties, the serial monitoring of the cardiac troponin level along with the absolute value would help to differentiate myocardial infarction from these many varied conditions, with the interval of serial assay being reduced to 3 hours. The aim of this review is to complement the advantages, to emphasize on proper interpretation of positive results, to appraise the challenges faced with the available cardiac troponin assays and need for further research to overcome them and build up the most ideal cardiac marker for diagnosing the myocardial infarction.

Methodologies for measurement of cardiac markers

Antibody-based tests are the primary technology used for clinical measurement of cardiac biomarkers in peripheral circulation. This article focuses on the principles of immunometric methods that have been applied to cardiac biomarkers of widespread clinical utility (CKMB, Troponins, and B-type natriuretic proteins) and of more recent clinical testing (ST2, Galectin-2, and myosin binding protein C). How these principles are applied in the design of immunometric assays and how they influence assay performance in quantifying cardiac biomarkers in biologic fluids (serum or plasma) is discussed.

Rapid exclusion of acute myocardial infarction in patients with undetectable troponin using a high-sensitivity assay

OBJECTIVES

This paper sought to evaluate whether high sensitivity troponin (hs-cTnT) can immediately exclude acute myocardial infarction (AMI) at a novel 'rule out' cut-off.

BACKGROUND

Subgroup analysis of recent evidence suggests that undetectable hs-cTnT may exclude AMI at presentation.

METHODS

In a cohort study, we prospectively enrolled patients with chest pain, evaluating them with standard troponin T and testing for hs-cTnT (Roche Diagnostics, Basel, Switzerland) at presentation. The primary outcome was a diagnosis of AMI. We also followed up patients for adverse events within 6 months. After subsequent clinical implementation of hs-cTnT, we again evaluated whether initially undetectable hs-cTnT ruled out a subsequent rise.

RESULTS

Of 703 patients in the cohort study, 130 (18.5%) had AMI, none of whom initially had undetectable hs-cTnT (sensitivity: 100.0%, 95% confidence interval [CI]: 95.1% to 100.0%, negative predictive value: 100.0%, 95% CI: 98.1% to 100.0%). This strategy would rule out AMI in 27.7% of patients, 2 (1.0%) of whom died or had AMI within 6 months (1 periprocedural AMI, 1 noncardiac death). We evaluated this approach in an additional 915 patients in clinical practice. Only 1 patient (0.6%) with initially undetectable hs-cTnT had subsequent elevation (to 17 ng/l), giving a sensitivity of 99.8% (95% CI: 99.1% to 100.0%) and a negative predictive value of 99.4% (95% CI: 96.6% to 100.0%).

CONCLUSIONS

Undetectable hs-cTnT at presentation has very high negative predictive value, which may be considered to rule out AMI, identifying patients at low risk of adverse events. Pending further validation, this strategy may reduce the need for serial testing and empirical treatment, enabling earlier reassurance for patients and fewer unnecessary evaluations and hospital admissions.

High-Sensitivity Cardiac Troponin I Measurement for Risk Stratification in a Stable High-Risk Population

BACKGROUND

Past investigations regarding the utility of high-sensitivity cardiac troponin I (cTnI) assays have been focused primarily on the acute coronary syndrome setting. We assessed whether such assays can predict future ischemic cardiovascular events in a stable high-risk population.

METHODS

We quantified serum cTnI using an investigational high-sensitivity assay (hs-cTnI IUO, Beckman Coulter) in 2572 participants from the Heart Outcomes Prevention Evaluation (HOPE) study. The derived ROC curve cutoff and the 99th percentile for the hs-cTnI assay were assessed by Kaplan–Meier and Cox analyses for the primary outcome [composite of myocardial infarction (MI), stroke, and cardiovascular death] at 4.5 years of follow-up. We also assessed individual outcomes (MI, stroke, cardiovascular death) and the combined outcome (MI/cardiovascular death) by regression analyses to determine hazard ratios (HRs) and c statistics in models that included established risk factors, C-reactive protein, and N-terminal pro-B–type natriuretic peptide (NT-proBNP).

RESULTS

Participants with hs-cTnI >6 ng/L (ROC cutoff) were at higher risk for the primary outcome (HR 1.38, 95% CI 1.09–1.76; P = 0.008, adjusted models). For the individual outcomes, participants with hs-cTnI above the 99th percentile (≥10 ng/L) had higher risk for cardiovascular death (HR 2.15, 95% CI 1.32–3.52; P = 0.002) and MI (HR 1.49, 95% CI 1.05–2.10; P = 0.025) but not stroke (HR 1.38, 95% CI 0.76–2.47; P = 0.288, adjusted models). Addition of hs-cTnI to an established risk model with NT-proBNP also yielded a higher c statistic for the combined outcome of MI/cardiovascular death.

CONCLUSIONS

The investigational Beckman Coulter hs-cTnI assay provides prognostic information for future MI and cardiovascular death in a stable high-risk population.

Sensitive and high sensitivity next generation cardiac troponin assays: more than just a name

In the 20 years that cardiac troponin testing has been available in clinical laboratories, the biomarker has revolutionised testing of patients with acute coronary syndromes. Cardiac troponin I and T testing has become the cornerstone for diagnosis of myocardial infarction and is useful for risk assessment and management of suspected acute coronary syndrome patients. As evidence and knowledge have evolved, it has become clear that even small troponin elevations are associated with adverse health outcomes. As a result there have been several generations of troponin assays, all toward tests that reliably detect lower concentrations of this critical analyte. Guidance for cardiac troponin interpretation has been in the form of myocardial infarction redefinition and evidence-based clinical and analytical guidelines. Although terminology naming generations for cardiac troponin assays has been inconsistent, state-of-the-art cardiac troponin assays are generally referred to as 'sensitive' assays and are in general compliance with analytical guidelines. Evidence shows that use of a sensitive troponin assay can result in diagnosis of myocardial infarction earlier. Next generation cardiac troponin I and T assays will likely be termed 'high sensitivity'; these assays should have the ability to measure troponin with a CV of total error of <10% at concentrations significantly lower than the 99 percentile of the normal reference population. As such, these assays should reliably measure troponin in most normal individuals and detect troponin changes (delta values) below the 99 percentile. This property may result in earlier ACS diagnosis and better management. Utilisation of high sensitivity troponin measurements may be useful for applications other than acute coronary syndromes including risk stratifying patients with renal insufficiency, heart failure, cardiac amyloid and screening elderly patients.

Elevated cardiac troponin I and functional recovery and disability in patients after aneurysmal subarachnoid hemorrhage

BACKGROUND

Patients with aneurysmal subarachnoid hemorrhage experience myocardial injury at the time of rupture, but its effect on functional recovery and disability is unclear.

OBJECTIVE

To describe the prevalence of myocardial injury, as indicated by high serum levels of cardiac troponin I (≥0.3 ng/mL), within the first 5 days after aneurysmal subarachnoid hemorrhage and the effect of the injury on 3-month functional recovery and disability.

METHODS

In a prospective longitudinal study, 239 patients with Hunt/Hess grade 3 or greater and/or Fisher grade 2 or greater at admission had serum level of troponin I measured on days 0 to 5. Patients were interviewed at 3 months to evaluate functional recovery (Glasgow Outcome Scale) and functional disability (Modified Rankin Scale). Statistics included χ² analysis, t tests, and binary logistic regression.

RESULTS

Troponin values were elevated in 33.5% of the patients, and few patients in either group had a history of coronary artery disease (7.4% with troponin levels ≥0.3 ng/mL vs 2.7% with levels <0.3 ng/mL, P = .12). Higher troponin levels were significantly related to age and Hunt/Hess and Fisher grades, but not race, and were significantly associated with poorer functional recovery (P < .001) and more functional disability (P < .001). Even after controls for age, race, and more severe Hunt/Hess grades, higher levels remained a significant predictor of poorer functional recovery (P = .04) and disability (P = .01). CONCLUSION Elevated levels of cardiac troponin I after aneurysmal subarachnoid hemorrhage are common in patients with no cardiac history, are associated with severity of the hemorrhage, and are independently predictive of poorer functional recovery and increased disability.

Troponin elevation in heart failure prevalence, mechanisms, and clinical implications

Circulating biomarkers have become increasingly important in diagnosing and risk stratifying patients with heart failure (HF). While the natriuretic peptides have received much focus, there is increasing interest in the role of circulating cardiac troponin (cTn) in detecting myocardial injury (often subclinical) in those with HF. Accumulating evidence suggests that patients with chronic and acute HF may have measurable levels of circulating cTn, whose detection and magnitude may have prognostic implications. Furthermore, as new, more sensitive cTn assays are being developed, larger numbers of HF patients are found to have detectable cTn with a persistent relationship between magnitude and outcome. This knowledge improves our ability to understand the mechanism of worsening HF, improve risk stratification, and detect potential injury related to new therapeutics in HF. As investigators begin to understand the relationship of detectable cTn to HF outcomes, as well as temporal changes in its magnitude, and its relationship to other circulating biomarkers, more insight may be gained into the progressive nature of cardiac dysfunction and the transition from chronic compensated to acute decompensated HF. Ultimately, this information might allow physicians to guide therapy, choose appropriate therapeutics, and improve HF outcomes.

Sensitive Cardiac Troponin Assays: Myth and Magic or a Practical Way Forward?

Cardiac troponins (cTn) are considered to be the ‘gold standard’ biomarkers for the diagnosis of acute coronary syndrome (ACS) a pathological spectrum which includes cardiac ischemia, angina, myocardial infarction and ultimately cardiac failure. The growing evidence base for the diagnostic and prognostic use of cTn in ACS has resulted in a universal redefinition of acute myocardial infarction (AMI). A diagnosis of AMI includes the detection of an elevated cTn (or CK-MB) with at least one measurement within 24 hours of the cardiac episode being >upper 99th percentile of a reference population, in conjunction with evidence of myocardial ischemia. A number of high sensitivity immunoassays with claims of superior imprecision and a definable 99th percentile have been produced. Clinically, these have two important impacts. First, there is a drive to change the values into whole numbers by the application of a unit change which carries the scope for confusion. Secondly, the near-normal Gaussian distribution of sensitive cTn in healthy subjects will increase the frequency of cTn positivity in the non-ACS population. The problem is to decipher if such minor elevations in cTn are of clinical concern. What is certain is that AMI remains a clinical not a biochemical diagnosis and the interpretation of cTn concentrations should be made according to the clinical context.

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.

Clinical applications of highly sensitive troponin assays

Cardiac troponin is the biomarker of choice for the diagnosis of acute myocardial infarction. Recent consensus recommendations have adopted a concentration of troponin above the 99th percentile of a healthy population to diagnose myocardial infarction. Until recently, there was no assay capable of achieving recommended precision; however, with the development of "highly sensitive" troponin assays, it is now possible to accurately measure troponin concentrations at and below the current 99th percentile of a healthy population. These assays have enormous potential in not only identifying more patients with acute myocardial infarction, and providing superior risk prediction in those so afflicted, in addition highly sensitive troponins assays may be useful for long-term risk assessment of the patient with coronary disease. In this article, we will review the clinical applications, novel concepts, challenges, and limitations of using highly sensitive troponins assays.