Development and Preliminary Clinical Validation of a High Sensitivity Assay for Cardiac Troponin Using a Capillary Flow (Single Molecule) Fluorescence Detector

Digital detection of proteins

This paper reviews methods for detecting proteins based on molecular digitization, i.e., the isolation and detection of single protein molecules or singulated ensembles of protein molecules. The single molecule resolution of these methods has resulted in significant improvements in the sensitivity of immunoassays beyond what was possible using traditional "analog" methods: the sensitivity of some digital immunoassays approach those of methods for measuring nucleic acids, such as the polymerase chain reaction (PCR). The greater sensitivity of digital protein detection has resulted in immuno-diagnostics with high potential societal impact, e.g., the early diagnosis and therapeutic intervention of Alzheimer's Disease. In this review, we will first provide the motivation for developing digital protein detection methods given the limitations in the sensitivity of analog methods. We will describe the paradigm shift catalyzed by single molecule detection, and will describe in detail one digital approach - which we call digital bead assays (DBA) - based on the capture and labeling of proteins on beads, identifying "on" and "off" beads, and quantification using Poisson statistics. DBA based on the single molecule array (Simoa) technology have sensitivities down to attomolar concentrations, equating to ∼10 proteins in a 200 μL sample. We will describe the concept behind DBA, the different single molecule labels used, the ways of analyzing beads (imaging of arrays and flow), the binding reagents and substrates used, and integration of these technologies into fully automated and miniaturized systems. We provide an overview of emerging approaches to digital protein detection, including those based on digital detection of nucleic acids labels, single nanoparticle detection, measurements using nanopores, and methods that exploit the kinetics of single molecule binding. We outline the initial impact of digital protein detection on clinical measurements, highlighting the importance of customized assay development and translational clinical research. We highlight the use of DBA in the measurement of neurological protein biomarkers in blood, and how these higher sensitivity methods are changing the diagnosis and treatment of neurological diseases. We conclude by summarizing the status of digital protein detection and suggest how the lab-on-a-chip community might drive future innovations in this field.

Recent Advances in Rapid and Highly Sensitive Detection of Proteins and Specific DNA Sequences Using a Magnetic Modulation Biosensing System

In early disease stages, biomolecules of interest exist in very low concentrations, presenting a significant challenge for analytical devices and methods. Here, we provide a comprehensive overview of an innovative optical biosensing technology, termed magnetic modulation biosensing (MMB), its biomedical applications, and its ongoing development. In MMB, magnetic beads are attached to fluorescently labeled target molecules. A controlled magnetic force aggregates the magnetic beads and transports them in and out of an excitation laser beam, generating a periodic fluorescent signal that is detected and demodulated. MMB applications include rapid and highly sensitive detection of specific nucleic acid sequences, antibodies, proteins, and protein interactions. Compared with other established analytical methodologies, MMB provides improved sensitivity, shorter processing time, and simpler protocols.

Digital plasmonic nanobubble detection for rapid and ultrasensitive virus diagnostics

Rapid and sensitive diagnostics of infectious diseases is an urgent and unmet need as evidenced by the COVID-19 pandemic. Here, we report a strategy, based on DIgitAl plasMONic nanobubble Detection (DIAMOND), to address this need. Plasmonic nanobubbles are transient vapor bubbles generated by laser heating of plasmonic nanoparticles (NPs) and allow single-NP detection. Using gold NPs as labels and an optofluidic setup, we demonstrate that DIAMOND achieves compartment-free digital counting and works on homogeneous immunoassays without separation and amplification steps. DIAMOND allows specific detection of respiratory syncytial virus spiked in nasal swab samples and achieves a detection limit of ~100 PFU/mL (equivalent to 1 RNA copy/µL), which is competitive with digital isothermal amplification for virus detection. Therefore, DIAMOND has the advantages including one-step and single-NP detection, direct sensing of intact viruses at room temperature, and no complex liquid handling, and is a platform technology for rapid and ultrasensitive diagnostics.

Optical modulation biosensing system for rapid detection of biological targets at low concentrations

In many sensitive assays, target molecules are tagged using fluorescently labeled probes and captured using magnetic beads. Here, we introduce an optical modulation biosensing (OMB) system, which aggregates the beads into a small detection area and separates the signal from the background noise by manipulating the laser beam in and out of the cluster of beads. Using the OMB system to detect human interleukin-8, we demonstrated a limit of detection of 0.02 ng/L and a 4-log dynamic range. Using Zika-positive and healthy individuals' serum samples, we show that the OMB-based Zika IgG serological assay has 96% sensitivity and 100% specificity.

Direct single-molecule imaging for diagnostic and blood screening assays

Every year, over 100 million units of donated blood undergo mandatory screening for HIV, hepatitis B, hepatitis C, and syphilis worldwide. Often, donated blood is also screened for human T cell leukemia-lymphoma virus, Chagas, dengue, Babesia, cytomegalovirus, malaria, and other infections. Several billion diagnostic tests are performed annually around the world to measure more than 400 biomarkers for cardiac, cancer, infectious, and other diseases. Considering such volumes, every improvement in assay performance and/or throughput has a major impact. Here, we show that medically relevant assay sensitivities and specificities can be fundamentally improved by direct single-molecule imaging using regular epifluorescence microscopes. In current microparticle-based assays, an ensemble of bound signal-generating molecules is measured as a whole. By contrast, we acquire intensity profiles to identify and then count individual fluorescent complexes bound to targets on antibody-coated microparticles. This increases the signal-to-noise ratio and provides better discrimination over nonspecific effects. It brings the detection sensitivity down to the attomolar (10^-18 M) for model assay systems and to the low femtomolar (10^-16 M) for measuring analyte in human plasma. Transitioning from counting single-molecule peaks to averaging pixel intensities at higher analyte concentrations enables a continuous linear response from 10^-18 to 10^-5 M. Additionally, our assays are insensitive to microparticle number and volume variations during the binding reaction, eliminating the main source of uncertainties in standard assays. Altogether, these features allow for increased assay sensitivity, wide linear detection ranges, shorter incubation times, simpler assay protocols, and minimal reagent consumption.

Single-Particle Counting Based on Digital Plasmonic Nanobubble Detection for Rapid and Ultrasensitive Diagnostics

Rapid and sensitive diagnostics of infectious diseases is an urgent and unmet need as evidenced by the COVID-19 pandemic. Here we report a novel strategy, based on DIgitAl plasMONic nanobubble Detection (DIAMOND), to address these gaps. Plasmonic nanobubbles are transient vapor bubbles generated by laser heating of plasmonic nanoparticles and allow single-particle detection. Using gold nanoparticles labels and an optofluidic setup, we demonstrate that DIAMOND achieves a compartment-free digital counting and works on homogeneous assays without separation and amplification steps. When applied to the respiratory syncytial virus diagnostics, DIAMOND is 150 times more sensitive than commercial lateral flow assays and completes measurements within 2 minutes. Our method opens new possibilities to develop single-particle digital detection methods and facilitate rapid and ultrasensitive diagnostics.

One Sentence Summary

Single-particle digital plasmonic nanobubble detection allows rapid and ultrasensitive detection of viruses in a one-step homogeneous assay.

Scanning single-molecule counting system for Eprobe with highly simple and effective approach

Here, we report a rapid and ultra-sensitive detection technique for fluorescent molecules called scanning single molecular counting (SSMC). The method uses a fluorescence-based digital measurement system to count single molecules in a solution. In this technique, noise is reduced by conforming the signal shape to the intensity distribution of the excitation light via a circular scan of the confocal region. This simple technique allows the fluorescent molecules to freely diffuse into the solution through the confocal region and be counted one by one and does not require statistical analysis. Using this technique, 28 to 62 aM fluorescent dye was detected through measurement for 600 s. Furthermore, we achieved a good signal-to-noise ratio (S/N = 2326) under the condition of 100 pM target nucleic acid by only mixing a hybridization-sensitive fluorescent probe, called Eprobe, into the target oligonucleotide solution. Combination of SSMC and Eprobe provides a simple, rapid, amplification-free, and high-sensitive target nucleic acid detection system. This method is promising for future applications to detect particularly difficult to design primers for amplification as miRNAs and other short oligo nucleotide biomarkers by only hybridization with high sensitivity.

Advances in Optical Single-Molecule Detection: En Route to Supersensitive Bioaffinity Assays

The ability to detect low concentrations of analytes and in particular low-abundance biomarkers is of fundamental importance, e.g., for early-stage disease diagnosis. The prospect of reaching the ultimate limit of detection has driven the development of single-molecule bioaffinity assays. While many review articles have highlighted the potentials of single-molecule technologies for analytical and diagnostic applications, these technologies are not as widespread in real-world applications as one should expect. This Review provides a theoretical background on single-molecule-or better digital-assays to critically assess their potential compared to traditional analog assays. Selected examples from the literature include bioaffinity assays for the detection of biomolecules such as proteins, nucleic acids, and viruses. The structure of the Review highlights the versatility of optical single-molecule labeling techniques, including enzymatic amplification, molecular labels, and innovative nanomaterials.

Direct single-molecule counting for immunoassay applications

Single-molecule methods offer specificity in studying complex systems and dynamics, but they also offer high sensitivity for basic enumeration. We apply single-molecule TIRF to immunoassays by counting the number of target molecules captured on a streptavidin surface. We demonstrate the utility of using single-molecule counting on eluted detection conjugate, following the capture and sandwich formation portions of the assay having been completed on microparticles. This approach is simple and effective, and creates the opportunity for a universal detection platform that can be used to perform a variety of diagnostic and blood screening assays. We take advantage of the low volume requirements of single-molecule detection and apply a sample reloading approach to concentrate sample onto the detection surface. Due to the high affinity of the streptavidin-biotin reaction, concentration through reloading is both quick and robust. These findings are demonstrated on a model system and in an HIV p24 antigen assay. Single-molecule detection techniques do not need to be complex to exhibit power and flexibility, and so can become valuable in the field of immunoassay diagnostics.

Cerebrospinal fluid and blood biomarkers for neurodegenerative dementias: An update of the Consensus of the Task Force on Biological Markers in Psychiatry of the World Federation of Societies of Biological Psychiatry

In the 12 years since the publication of the first Consensus Paper of the WFSBP on biomarkers of neurodegenerative dementias, enormous advancement has taken place in the field, and the Task Force takes now the opportunity to extend and update the original paper. New concepts of Alzheimer's disease (AD) and the conceptual interactions between AD and dementia due to AD were developed, resulting in two sets for diagnostic/research criteria. Procedures for pre-analytical sample handling, biobanking, analyses and post-analytical interpretation of the results were intensively studied and optimised. A global quality control project was introduced to evaluate and monitor the inter-centre variability in measurements with the goal of harmonisation of results. Contexts of use and how to approach candidate biomarkers in biological specimens other than cerebrospinal fluid (CSF), e.g. blood, were precisely defined. Important development was achieved in neuroimaging techniques, including studies comparing amyloid-β positron emission tomography results to fluid-based modalities. Similarly, development in research laboratory technologies, such as ultra-sensitive methods, raises our hopes to further improve analytical and diagnostic accuracy of classic and novel candidate biomarkers. Synergistically, advancement in clinical trials of anti-dementia therapies energises and motivates the efforts to find and optimise the most reliable early diagnostic modalities. Finally, the first studies were published addressing the potential of cost-effectiveness of the biomarkers-based diagnosis of neurodegenerative disorders.

Effect of Health and Training on Ultrasensitive Cardiac Troponin in Marathon Runners

PURPOSE

Cardiac troponin (cTn) is the gold standard biomarker for assessing cardiac damage. Previous studies have demonstrated increases in plasma cTn because of extreme exercise, including marathon running. We developed an easy-to-use, ultrasensitive assay for cardiac troponin I (cTnI) by combining single-molecule counting (SMC™) technology with dried blood spot (DBS) collection techniques and validated the assay on a cohort of marathon runners by correlating postmarathon cTnI elevations with training or risk variables.

METHODS

An SMC-DBS method was developed for accurate and reproducible measurement of cTnI in fingerstick whole blood. Samples were collected from 42 runners both before and immediately after running a marathon. A similar collection was obtained from 22 non-running control individuals. Pre- and postrace questionnaires containing health and training variables were correlated with cTnI concentration.

RESULTS

The assay quantified cTnI in all controls and marathon runners, both before and after the race. Prerace concentrations were significantly higher in marathon runners vs controls (median 3.1 vs 0.4 pg/mL; P < 0.0001). Immediate postmarathon concentrations were increased in 98% of runners (median elevation, 40.5 pg/mL; P < 0.001), including many above traditional cutoffs for acute myocardial infarction. Several health and training variables trended toward significant correlation with cTnI elevations.

CONCLUSION

While further studies are needed to better understand the mechanisms and clinical implications of exercise-induced cTnI elevations, the present study suggests several variables that may be associated with such elevations and demonstrates a simple, cost-effective method for monitoring cTnI during exercise, managing chronic disease, and/or for assessing risk in large populations.

Advances in Proteomic Techniques for Cytokine Analysis: Focus on Melanoma Research

Melanoma is a skin cancer with permanently increasing incidence and resistance to therapies in advanced stages. Reports of spontaneous regression and tumour infiltration with T-lymphocytes makes melanoma candidate for immunotherapies. Cytokines are key factors regulating immune response and intercellular communication in tumour microenvironment. Cytokines may be used in therapy of melanoma to modulate immune response. Cytokines also possess diagnostic and prognostic potential and cytokine production may reflect effects of immunotherapies. The purpose of this review is to give an overview of recent advances in proteomic techniques for the detection and quantification of cytokines in melanoma research. Approaches covered span from mass spectrometry to immunoassays for single molecule detection (ELISA, western blot), multiplex assays (chemiluminescent, bead-based (Luminex) and planar antibody arrays), ultrasensitive techniques (Singulex, Simoa, immuno-PCR, proximity ligation/extension assay, immunomagnetic reduction assay), to analyses of single cells producing cytokines (ELISpot, flow cytometry, mass cytometry and emerging techniques for single cell secretomics). Although this review is focused mainly on cancer and particularly melanoma, the discussed techniques are in general applicable to broad research field of biology and medicine, including stem cells, development, aging, immunology and intercellular communication.

Analytically Sensitive Protein Detection in Microtiter Plates by Proximity Ligation with Rolling Circle Amplification

BACKGROUND

Detecting proteins at low concentrations in plasma is crucial for early diagnosis. Current techniques in clinical routine, such as sandwich ELISA, provide sensitive protein detection because of a dependence on target recognition by pairs of antibodies, but detection of still lower protein concentrations is often called for. Proximity ligation assay with rolling circle amplification (PLARCA) is a modified proximity ligation assay (PLA) for analytically specific and sensitive protein detection via binding of target proteins by 3 antibodies, and signal amplification via rolling circle amplification (RCA) in microtiter wells, easily adapted to instrumentation in use in hospitals.

METHODS

Proteins captured by immobilized antibodies were detected using a pair of oligonucleotide-conjugated antibodies. Upon target recognition these PLA probes guided oligonucleotide ligation, followed by amplification via RCA of circular DNA strands that formed in the reaction. The RCA products were detected by horseradish peroxidase-labeled oligonucleotides to generate colorimetric reaction products with readout in an absorbance microplate reader.

RESULTS

We compared detection of interleukin (IL)-4, IL-6, IL-8, p53, and growth differentiation factor 15 (GDF-15) by PLARCA and conventional sandwich ELISA or immuno-RCA. PLARCA detected lower concentrations of proteins and exhibited a broader dynamic range compared to ELISA and iRCA using the same antibodies. IL-4 and IL-6 were detected in clinical samples at femtomolar concentrations, considerably lower than for ELISA.

CONCLUSIONS

PLARCA offers detection of lower protein levels and increased dynamic ranges compared to ELISA. The PLARCA procedure may be adapted to routine instrumentation available in hospitals and research laboratories.

[Interaction between heart and brain in sudden cardiac death]

The heart and brain are constantly interacting under normal physiological conditions. This interaction is under the control of the autonomic nervous system with parasympathetic and sympathetic nerve fibers including the participating brain structures. Pathological conditions, such as epilepsy and ischemic cerebral stroke influence heart function, especially the frequency and may result in severe arrhythmia. An asymmetric influence of the left and right brain hemispheres on the heart rate is still under debate. Conversely, the influence of the heart in cases of acute cardiac arrest on brain function is equally relevant and a common clinical problem after resuscitation. We review the damaging cascade of global cerebral hypoxia and the value of different diagnostic procedures as well as the ethical problem of the point in time of termination of consciousness and the instruments for estimating the prognosis.

Highly sensitive ligand-binding assays in pre-clinical and clinical applications: immuno-PCR and other emerging techniques

Recombinant DNA technology and corresponding innovations in molecular biology, chemistry and medicine have led to novel therapeutic biomacromolecules as lead candidates in the pharmaceutical drug development pipelines. While monoclonal antibodies and other proteins provide therapeutic potential beyond the possibilities of small molecule drugs, the concomitant demand for supportive bioanalytical sample testing creates multiple novel challenges. For example, intact macromolecules can usually not be quantified by mass-spectrometry without enzymatic digestion and isotopically labeled internal standards are costly and/or difficult to prepare. Classical ELISA-type immunoassays, on the other hand, often lack the sensitivity required to obtain pharmacokinetics of low dosed drugs or pharmacodynamics of suitable biomarkers. Here we summarize emerging state-of-the-art ligand-binding assay technologies for pharmaceutical sample testing, which reveal enhanced analytical sensitivity over classical ELISA formats. We focus on immuno-PCR, which combines antibody specificity with the extremely sensitive detection of a tethered DNA marker by quantitative PCR, and alternative nucleic acid-based technologies as well as methods based on electrochemiluminescence or single-molecule counting. Using case studies, we discuss advantages and drawbacks of these methods for preclinical and clinical sample testing.

Emerging technologies to increase ligand binding assay sensitivity

Ligand binding assays (LBAs) have been the method of choice for protein analyte measurements for more than four decades. Over the years, LBA methods have improved in sensitivity and achieved larger dynamic ranges by using alternative detection systems and new technologies. As a consequence, the landscape and application of immunoassay platforms has changed dramatically. The introduction of bead-based methods, coupled with single molecule detection standardization and the ability to amplify assay signals, has improved the sensitivity of many immunoassays, in some cases by several logs of magnitude. Three promising immunoassay platforms are described in this article: Single Molecule Counting (SMC™) from Singulex Inc, Single Molecule Arrays (Simoa™) from Quanterix Corporation, and Immuno-PCR (Imperacer®) from Chimera Biotec GmbH. These platforms have the potential to significantly improve immunoassay sensitivity and thereby address the bioanalytical needs and challenges faced during biopharmaceutical drug development.

Chimeric recombinant antibody fragments in cardiac troponin I immunoassay

OBJECTIVES

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

DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

High sensitivity cardiac troponin T in patients with immunoglobulin light chain amyloidosis

OBJECTIVES

To define whether the high sensitivity cardiac troponin T (hs-cTnT) assay in patients with immunoglobulin light chain amyloidosis (AL) improves risk prediction.

BACKGROUND

Cardiac involvement is the major cause of death in patients with AL amyloidosis. Risk stratification is facilitated by cardiac biomarkers such as cardiac troponin T (cTnT) and N-terminal pro B-type natriuretic peptide (NT-proBNP).

METHODS

Stored serum from patients with newly diagnosed AL was used to measure hs-cTnT, cTnT, and NT-proBNP. Survival modelling was performed.

RESULTS

The direct numeric result from hs-cTnT measurement cannot merely be substituted for a cTnT measurement in the Mayo AL staging system. The performance of the receiver operator curve derived an hs-cTnT cut-point of 54 ng/L which improves on the value of 35 ng/L validated with the prior iteration of the assay. An alternate staging option using hs-cTnT alone-using the two thresholds 14 ng/L and 54 ng/L-performs as well as either the original Mayo AL staging system or other systems incorporating hs-cTnT. On multivariate analysis, an hs-cTnT alone staging system was independent of period of diagnosis, type of therapy, and NT-proBNP value, the last of which dropped out of the model. Alternate models were explored, but none performed better than the original system or the new hs-cTnT system. Thus, hs-cTnT can be used alone for the staging of disease prognosis.

CONCLUSIONS

A survival model based on hs-cTnT improves the prognostic staging of patients with AL amyloidosis, relegating NT-proBNP to a measure of cardiac response.

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

OBJECTIVE

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

DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Single resting hsTnT level predicts abnormal myocardial stress test in acute chest pain patients with normal initial standard troponin

OBJECTIVES

The goal of this study was to determine the ability of a single, resting high-sensitivity troponin T (hsTnT) measurement to predict abnormal myocardial perfusion imaging (MPI) in patients presenting with acute chest pain to the emergency department (ED).

BACKGROUND

HsTnT assays precisely detect very low levels of troponin T, which may be a surrogate for the presence and extent of myocardial ischemia.

METHODS

We included all patients from the ROMICAT I (Rule Out Myocardial Infarction Using Computer Assisted Tomography) trial, an observational cohort study, who underwent both single-photon emission computed tomography (SPECT)-MPI stress testing and 64-slice computed tomography angiography (CTA) and in whom hsTnT measurements were available. We assessed the discriminatory value of hsTnT for abnormal SPECT-MPI and the association of reversible myocardial ischemia by SPECT-MPI and the extent of coronary atherosclerosis by CTA to hsTnT levels.

RESULTS

Of the 138 patients (mean age 54 ± 11 years, 46% male), 19 (13.7%) had abnormal SPECT-MPI. Median hsTnT levels were significantly different between patients with normal and abnormal SPECT-MPI (9.41 pg/ml [interquartile range (IQR): 5.73 to 19.20 pg/ml] vs. 4.89 pg/ml [IQR: 2.34 to 7.68 pg/ml], p = 0.001). Sensitivity of 80% and 90% to detect abnormal SPECT-MPI was reached at hsTnT levels as low as 5.73 and 4.26 pg/ml, respectively. Corresponding specificity was 62% and 46%, and negative predictive value was 96% and 96%, respectively. HsTnT levels had good discriminatory ability for prediction of abnormal SPECT-MPI (area under the curve: 0.739, 95% confidence interval: 0.609 to 0.868). Both reversible myocardial ischemia and the extent of coronary atherosclerosis (combined model r(2) = 0.19 with partial of r(2) = 0.12 and r(2) = 0.05, respectively) independently and incrementally predicted the measured hsTnT levels.

CONCLUSIONS

In patients with acute chest pain, myocardial perfusion abnormalities and coronary artery disease are predicted by resting hsTnT levels. Prospective evaluations are warranted to confirm whether resting hsTnT could serve as a powerful triage tool in chest pain patients in the ED before diagnostic testing and improve the effectiveness of patient management.

Quantitative determination of human interleukin 22 (IL-22) in serum using Singulex-Erenna® technology

Interleukin-22 (IL-22) is a key mediator of inflammatory processes associated with diseases such as psoriasis, inflammatory bowel disease and rheumatoid arthritis. The measurement of this cytokine in human plasma may provide insight into safety, pharmacodynamics and efficacy of drugs targeting inflammatory pathways. However, commonly used immunoassays are not sufficiently sensitive to measure baseline concentrations of IL-22. Here we describe the analytical validation of an ultrasensitive assay for the measurement of IL-22 in human serum using the Erenna® system by Singulex (Alameda, CA). The lower limit of quantification (LLOQ) of the Erenna assay estimated at 0.2pg/mL was sensitive enough to measure IL-22 in all human serum samples tested. The assay ranged from 0.2 to 100.0pg/mL and showed good dilution linearity. The inter-assay and intra-assay imprecision were <9% and <7% CV respectively. The accuracy determined by spiked recovery in serum samples was >86%. In addition, the results using Erenna assay correlated well with those using the IL-22 Quantikine immunoassay (R&D Systems, Minneapolis, MN) with a coefficient R(2) of 0.9285. However the Erenna assay showed an improved sensitivity by approximately 2 logs. These results show that this novel assay offers a significant improvement over previous methods for high-sensitive quantitative measurement of IL-22 in human serum samples.

Current applications of cardiac troponin T for the diagnosis of myocardial damage

Biochemical markers of myocardial injury play an important role in the diagnosis of cardiovascular diseases. Measurement of cardiac biomarkers is one of the most important diagnostic tests in acute myocardial infarction (AMI), heart failure, and other cardiovascular disorders. Recently, the European Society of Cardiology, the American College of Cardiology Foundation, the American Heart Association, and the World Heart Federation have published a consensus definition of AMI that includes a detailed guideline for the assessment of biochemical markers in suspected disease. The cardiac troponins (cTI and cTnT) were recommended as preferred markers of myocardial necrosis in this setting. Herein, we review cardiac troponin biochemistry, the performance characteristics of cTnT assays, and optimal utilization of troponin in patients with proven or possible cardiovascular disease. We also discuss the use of troponin tests, with emphasis on cTnT, in different clinical situations in which its levels may be elevated.

Prognostic utility of novel biomarkers of cardiovascular stress: the Framingham Heart Study

BACKGROUND

Biomarkers for predicting cardiovascular events in community-based populations have not consistently added information to standard risk factors. A limitation of many previously studied biomarkers is their lack of cardiovascular specificity.

METHODS AND RESULTS

To determine the prognostic value of 3 novel biomarkers induced by cardiovascular stress, we measured soluble ST2, growth differentiation factor-15, and high-sensitivity troponin I in 3428 participants (mean age, 59 years; 53% women) in the Framingham Heart Study. We performed multivariable-adjusted proportional hazards models to assess the individual and combined ability of the biomarkers to predict adverse outcomes. We also constructed a "multimarker" score composed of the 3 biomarkers in addition to B-type natriuretic peptide and high-sensitivity C-reactive protein. During a mean follow-up of 11.3 years, there were 488 deaths, 336 major cardiovascular events, 162 heart failure events, and 142 coronary events. In multivariable-adjusted models, the 3 new biomarkers were associated with each end point (P<0.001) except coronary events. Individuals with multimarker scores in the highest quartile had a 3-fold risk of death (adjusted hazard ratio, 3.2; 95% confidence interval, 2.2-4.7; P<0.001), 6-fold risk of heart failure (6.2; 95% confidence interval, 2.6-14.8; P<0.001), and 2-fold risk of cardiovascular events (1.9; 95% confidence interval, 1.3-2.7; P=0.001). Addition of the multimarker score to clinical variables led to significant increases in the c statistic (P=0.005 or lower) and net reclassification improvement (P=0.001 or lower).

CONCLUSION

Multiple biomarkers of cardiovascular stress are detectable in ambulatory individuals and add prognostic value to standard risk factors for predicting death, overall cardiovascular events, and heart failure.

Variation of cardiac troponin I and T measured with sensitive assays in emergency department patients with noncardiac chest pain

BACKGROUND

New-generation high-sensitivity assays for cardiac troponin have lower detection limits and less imprecision than earlier assays. Reference 99th-percentile cutoff values for these new assays are also lower, leading to higher frequencies of positive test results. When cardiac troponin concentrations are minimally increased, serial testing allows discrimination of myocardial infarction from other causes of increased cardiac troponin. We assessed various measures of short-term variation, including absolute concentration changes, reference change values (RCVs), and indices of individuality (II) for 2 cardiac troponin assays in emergency department (ED) patients.

METHODS

We collected blood from patients presenting with cardiac chest pain upon arrival in the ED and 2, 6, and 12 h later. Cardiac troponin was measured with the high-sensitivity cardiac troponin T (hs-cTnT) assay (Roche Diagnostics) and a sensitive cTnI assay (Siemens Diagnostics). Cardiac troponin results from 67 patients without acute coronary syndrome or stable angina were used in calculating absolute changes in cardiac troponin, RCVs, and II.

RESULTS

The 95th percentiles for absolute change in cardiac troponin were 8.3 ng/L for hs-cTnT and 28 ng/L for cTnI. Within-individual and total CVs were 11% and 14% for hs-cTnT and 18% and 21% for cTnI, respectively. RCVs were 38% (hs-cTnT) and 57% (cTnI). The corresponding log-normal RCVs were +46%/-32% for hs-cTnT and +76%/-43% for cTnI. II values were 0.31 (cTnI) and 0.12 (hs-cTnT).

CONCLUSIONS

The short-term variations and IIs of cardiac troponin were low in ED patients free of ischemic myocardial necrosis. The detection of cardiac troponin variation exceeding reference thresholds can help to identify ED patients with acute myocardial necrosis whereas variation within these limits renders acute coronary syndrome unlikely.

Sensitive cardiac troponin in the diagnosis and risk stratification of acute heart failure

BACKGROUND

The aim of our study was to investigate the diagnostic and prognostic value of a sensitive cardiac troponin I (s-cTnI) assay in patients with acute heart failure (AHF).

METHODS

Sensitive cardiac troponin I was measured in 667 consecutive patients at presentation to the emergency department with acute dyspnoea. Three s-cTnI strata were predefined: below the limit of detection (<0.01 μg L(-1) , undetectable), detectable but still within the normal range (0.01-0.027 μg L(-1) ) and increased (≥0.028 μg L(-1) , ≥99th percentile). The final diagnosis was adjudicated by two independent cardiologists blinded to the s-cTnI levels. Median follow-up in patients with AHF was 371 days.

RESULTS

Levels of s-cTnI were higher in patients with AHF (n = 377, 57%) compared to patients with noncardiac causes of acute dyspnoea (median 0.02 vs. <0.01 μg L(-1) , P < 0.001). In patients with AHF, in-hospital mortality increased with increasing s-cTnI in the three strata (2%, 5% and 14%, P < 0.001). One-year mortality also increased with increasing s-cTnI (21%, 33% and 47%, P < 0.001). s-cTnI remained an independent predictor of 1-year mortality [adjusted odds ratio 1.03 for each increase of 0.1 μg L(-1) , 95% confidence interval (CI) 1.02-1.05, P < 0.001] after adjustment for other risk factors including B-type natriuretic peptide. The net reclassification improvement was 68% (P < 0.001), and absolute integrated discrimination improvement was 0.18 (P < 0.001). The diagnostic accuracy of s-cTnI for the diagnosis of AHF as quantified by the area under the receiver operating characteristic curve was 0.78 (95% CI, 0.75-0.82).

CONCLUSIONS

Sensitive cardiac troponin I is a strong predictor of short- and long-term prognosis in AHF that helps to reclassify patients in terms of mortality risk. Detectable levels of s-cTnI, even within the normal range, are independently associated with mortality.

Exercise-induced cardiac injury: evidence from novel imaging techniques and highly sensitive cardiac troponin assays

Prolonged endurance exercise in humans has been associated with an acute impairment in diastolic and systolic cardiac function and the release of cardiac troponin. In this chapter, we review recent evidence from studies using novel echocardiographic parameters and highly sensitive cardiac troponin assays. We demonstrate that the mechanics of left and right ventricular functions are acutely impaired after completion of prolonged exercise and that this reduction in function is likely multifactorial in etiology. However, we highlight that exercise-induced cardiac troponin release is not a marker of exercise-induced pathology but likely a physiologic response to exercise. Finally, we discuss the potential link between prolonged exercise and the increased incidence of cardiac pathology in veteran athletes.

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.