Interaction of heparin with human cardiac troponin complex and its influence on the immunodetection of troponins in human blood samples

OBJECTIVES

Heparin is a highly charged polysaccharide used as an anticoagulant to prevent blood coagulation in patients with presumed myocardial infarction and to prepare heparin plasma samples for laboratory tests. There are conflicting data regarding the effects of heparin on the measurement of cardiac isoforms of troponin I (cTnI) and troponin T (cTnT), which are used for the immunodiagnosis of acute myocardial infarction. In this study, we investigated the influence of heparin on the immunodetection of human cardiac troponins.

METHODS

Gel filtration (GF) techniques and sandwich fluoroimmunoassay were performed. The regions of сTnI and cTnT that are affected by heparin were investigated with a panel of anti-cTnI and anti-cTnT monoclonal antibodies, specific to different epitopes.

RESULTS

Heparin was shown to bind to the human cardiac full-size ternary troponin complex (ITC-complex) and free cTnT, which increased their apparent molecular weights in GF studies. Heparin did not bind to the low molecular weight ITC-complex and to binary cTnI-troponin С complex. We did not detect any sites on cTnI in the ITC-complex that were specifically affected by heparin. In contrast, cTnT regions limited to approximately 69-99, 119-138 and 145-164 amino acid residues (aar) in the ITC-complex and a region that lies approximately between 236 and 255 aar of free cTnT were prone to heparin influence.

CONCLUSIONS

Heparin binds to the ITC-complex via cTnT, interacting with several sites on the N-terminal and/or central parts of the cTnT molecule, which might influence the immunodetection of analytes in human blood.

Performance evaluation of the high sensitive troponin I assay on the Atellica IM analyser

Introduction

The Fourth Universal Definition of Myocardial Infarction Global Taskforce recommends the use of high sensitive troponin (hs-Tn) assays in the diagnosis of acute myocardial infarction. We evaluated the analytical performance of the Atellica IM High-sensitivity Troponin I Assay (hs-TnI) (Siemens Healthcare Diagnostics Inc., Tarrytown, USA) and compared its performance to other hs-TnI assays (Siemens Advia Centaur, Dimension Vista, Dimension EXL, and Abbott Architect (Wiesbaden, Germany)) at one or more sites across Europe.

Materials and methods

Precision, detection limit, linearity, method comparison, and interference studies were performed according to Clinical and Laboratory Standards Institute protocols. Values in 40 healthy individuals were compared to the manufacturer’s cut-offs. Sample turnaround time (TAT) was examined.

Results

Imprecision repeatability CVs were 1.1–4.7% and within-lab imprecision were 1.8–7.6% (10.0–25,000 ng/L). The limit of blank (LoB), detection (LoD), and quantitation (LoQ) aligned with the manufacturer’s values of 0.5 ng/L, 1.6 ng/L, and 2.5 ng/L, respectively. Passing-Bablok regression demonstrated good correlations between Atellica IM analyser with other systems; some minor deviations were observed. All results in healthy volunteers fell below the 99th percentile URL, and greater than 50% of each sex demonstrated values above the LoD. No interference was observed for biotin (≤ 1500 µg/L), but a slight bias at 5.0 g/L haemoglobin and 50 ng/L Tn was observed. TAT from was fast (mean time = 10.9 minutes) and reproducible (6%CV).

Conclusions

Real-world analytical and TAT performance of the hs-TnI assay on the Atellica IM analyser make this assay fit for routine use in clinical laboratories.

Storage conditions, sample integrity, interferences, and a decision tool for investigating unusual high-sensitivity cardiac troponin results

The current definition of high-sensitivity cardiac troponin (hs-cTn) assays is laboratory-based and their analytical attributes and characteristics have drawn significant attention in the literature at least partly due to the lower concentration cut-offs and changes in concentrations (i.e., deltas) employed in different algorithms and pathways to manage patient care. We propose that pre-analytical conditions such as sample type, storage conditions, and other interferences may also have a significant impact on hs-cTn concentrations and clinical management. The purpose of this literature review is to provide a summary of important pre-analytical and interference studies affecting hs-cTn concentrations. A breakdown of the literature for the major diagnostic companies providing core laboratory instrumentation (i.e., Abbott, Beckman, Ortho, Roche, and Siemens) is also provided. Finally, three cases are highlighted where knowledge of pre-analytical factors aids the hs-cTn clinically discordant investigations. This review highlights the importance of pre-analytical variables, especially storage condition, sample handling, and blood tubes used (i.e., sample type) when interpreting hs-cTn assays. Additional studies are needed to further elaborate on pre-analytical variables (i.e., centrifugation, sample type, stability) and interferences for all hs-cTn assays in clinical use, as knowledge of these variables may aid in hs-cTn clinically discordant investigations.

Fiber-integrated WGM optofluidic chip enhanced by microwave photonic analyzer for cardiac biomarker detection with ultra-high resolution

Cardiac troponin I (cTnI) plays an important role in emergency diagnosis of cardiovascular diseases, which exists predominately in the form of cardiac troponin I-C (cTnI-C) complex. We proposed a fiber-integrated optofluidic chip immunosensor with time-delay-dispersion based microwave photonic analyzer (MPA) for cTnI-C detection. The whispering gallery mode (WGM) fiber probe was fabricated by embedding a polydopamine functionalized hollow glass microsphere (HGMS) into the etched capillary-fiber structure, and the WGMs could be excited through the efficient coupling between the thin-wall capillary and the HGMS. The reflective WGM optofluidic chip functioned as a wavelength tuner to construct fiber ring laser cavity, whose laser output wavelength was cTnI-C concentration-dependent. The tiny wavelength variation of sensing laser was converted into a radio-frequency (RF) response, which was retrieved by measuring the change of RF-domain free spectrum range (FSR) in time-delay-dispersion based MPA, and the quantitative detection of cTnI-C complex can be achieved with high resolution. Experimental results show that this immunosensor had a limit of detection (LOD) of 0.59 ng/mL, and a detection resolution of 1.2 fg/mL. The relative resolving power was 10²-10⁴-fold higher than that of others optical fiber cTnI biosensors. The proposed fiber-integrated optofluidic chip provides an innovative lab-on-chip diagnostic tool for myocardial damage.

Analytical assessment and performance of the 0/3h algorithm with novel high sensitivity cardiac troponin I

BACKGROUND

Recently, Ortho Clinical Diagnostics have launched a high sensitivity cardiac troponin I assay adapted on Vitros3600 / 5600. We aimed at evaluating the analytical and clinical performances using the 0/3-hour algorithm, of the Ortho hs-cTnI assay on the Vitros 3600® (Ortho Clinical Diagnostics, Illkirch, France) analyzer with comparison to Roche hs-cTnT assay on the Cobas8000/e801® module (Roche diagnostics, Meylan, France) and the Abbott STAT hs-cTnI assay on the Alinity i® (Abbott, Rungis, France) analyzer.

METHODS

Imprecision studies, linearity, limit of detection, and the interference to hemolysis were performed for Ortho hs-cTnI assay. The concordance study was based on results of troponin obtained from 160 patients with chest pain to the emergency department. Testing was performed simultaneously measuring the Roche hs-cTnT and the Ortho hs-cTnI, then on remaining sample the concentration of Abbott hs-cTnI (n = 150). We applied the 0/3h algorithm to rule out/rule in, in acute myocardial infarction.

RESULTS

Analytical performances were acceptable and in accordance with manufacturer's data. For late presenters 100, 92.8 and 88.8% patients could be rule-out with Roche, Ortho and Abbott assay, respectively with one NSTEMI missed with both hs-TnI assays. Applying the hs-cTn cut-offs from 0/3-hour algorithm, 107 (66.8%) could be rule out with Roche hs-cTnT with no AMI missed (sensitivity 100% [95%CI: 90.5 to 100] and NPV 100%); 89 with Ortho hs-cTnI (sensitivity 97.3% [95%CI: 85.8-99.9] and NPV 98.8% [95%CI:92.7-99.8]); and 61 with Abbott hs-cTnI (sensitivity 97% [95%CI: 84.2-99.9] and NPV 98.4% [95%CI: 89.8-99.7]). For rule-in, 23.7% (n = 37) from the total population would be designated in this group, with a specificity of 86.9% (95%CI: 79.7-92.4) and PPV of 69.8% (95%CI: 59.4-78.5) vs specificity of 72.3% (95%CI:63.5-80.0) and PPV of 51.4% (95%CI: 44.1-58.2)with Roche hs-cTnT vs Ortho hs-cTnI respectively; and with Abbott, 33 patients had constitued this group with a specificity of 52.1% (95%CI:42.7-61.4) and PPV of 36.4% (95%CI: 32.0-41.0).

CONCLUSION

In conclusion, according to ESC guidelines, our results indicate that the Ortho hs-cTnI assay for the Vitros 3600 instrument is a method that may be used in the clinical practice using 0/3-hour algorithm.

Microfluidic Impedance Biosensor Chips Using Sensing Layers Based on DNA-Based Self-Assembled Monolayers for Label-Free Detection of Proteins

A microfluidic chip for electrochemical impedance spectroscopy (EIS) is presented as bio-sensor for label-free detection of proteins by using the example of cardiac troponin I. Troponin I is one of the most specific diagnostic serum biomarkers for myocardial infarction. The microfluidic impedance biosensor chip presented here consists of a microscope glass slide serving as base plate, sputtered electrodes, and a polydimethylsiloxane (PDMS) microchannel. Electrode functionalization protocols were developed considering a possible charge transfer through the sensing layer, in addition to analyte-specific binding by corresponding antibodies and reduction of nonspecific protein adsorption to prevent false-positive signals. Reagents tested for self-assembled monolayers (SAMs) on gold electrodes included thiolated hydrocarbons and thiolated oligonucleotides, where SAMs based on the latter showed a better performance. The corresponding antibody was covalently coupled on the SAM using carbodiimide chemistry. Sampling and measurement took only a few minutes. Application of a human serum albumin (HSA) sample, 1000 ng/mL, led to negligible impedance changes, while application of a troponin I sample, 1 ng/mL, led to a significant shift in the Nyquist plot. The results are promising regarding specific detection of clinically relevant concentrations of biomarkers, such as cardiac markers, with the newly developed microfluidic impedance biosensor chip.

Analytical assessment of ortho clinical diagnostics high-sensitivity cardiac troponin I assay

Objectives

To analytically evaluate Ortho Clinical Diagnostics VITROS high-sensitivity cardiac troponin I (hs-cTnI) assay in specific matrices with comparison to other hs-cTn assays.

Methods

The limit of detection (LoD), imprecision, interference and stability testing for both serum and lithium heparin (Li-Hep) plasma for the VITROS hs-cTnI assay was determined. We performed Passing-Bablok regression analyses between sample types for the VITROS hs-cTnI assay and compared them to the Abbott ARCHITECT, Beckman Access and the Siemens ADVIA Centaur hs-cTnI assays. We also performed Receiver-operating characteristic curve analyses with the area under the curve (AUC) determined in an emergency department (ED)-study population (n=131) for myocardial infarction (MI).

Results

The VITROS hs-cTnI LoD was 0.73 ng/L (serum) and 1.4 ng/L (Li-Hep). Stability up to five freeze-thaws was observed for the Ortho hs-cTnI assay, with the analyte stability at room temperature in serum superior to Li-Hep with gross hemolysis also affecting Li-Hep plasma hs-cTnI results. Comparison of Li-Hep to serum concentrations (n=202), yielded proportionally lower concentrations in plasma with the VITROS hs-cTnI assay (slope=0.85; 95% confidence interval [CI]:0.83-0.88). In serum, the VITROS hs-cTnI concentrations were proportionally lower compared to other hs-cTnI assays, with similar slopes observed between assays in samples frozen <-70 °C for 17 years (ED-study) or in 2020. In the ED-study, the VITROS hs-cTnI assay had an AUC of 0.974 (95%CI:0.929-0.994) for MI, similar to the AUCs of other hs-cTn assays.

Conclusions

Lack of standardization of hs-cTnI assays across manufacturers is evident. The VITROS hs-cTnI assay yields lower concentrations compared to other hs-cTnI assays. Important differences exist between Li-Hep plasma and serum, with evidence of stability and excellent clinical performance comparable to other hs-cTn assays.

Using the clinical chemistry score in the emergency department to detect adverse cardiac events: a diagnostic accuracy study

BACKGROUND

The ability to rule out or in a major adverse cardiac event (MACE) in patients with suspected acute coronary syndrome at emergency department (ED) presentation would be beneficial to patient care and the health care system. The clinical chemistry score (CCS) was evaluated in this context.

METHODS

This diagnostic accuracy study evaluated 2 different ED cohorts with suspected acute coronary syndrome. For patients in cohort 1, who presented to the ED of 3 hospitals in Hamilton, Ontario, between May and August 2013, retrospective measurements were taken using the Ortho Clinical Diagnostics high-sensitivity cardiac troponin I (hs-cTnI) assay; for patients in cohort 2, who presented to the ED of the same 3 hospitals in Hamilton between November 2012 and February 2013, an ED cardiac presentation blood test panel was performed with the Abbott Diagnostics hs-cTnI assay. The sensitivity and specificity of the CCS (cut-offs of ≥ 1 and 5) and hs-cTnI alone (published cut-offs) were compared for MACE (composite of death, myocardial infarction, unstable angina, revascularization) at 30 days for both cohorts and at 90 days for cohort 2.

RESULTS

The incidence of MACE at 30 days was higher in cohort 1 (n = 1058) (19.4%, 95% confidence interval [CI] 16.8%-22.2%) than in cohort 2 (n = 5974) (14.6%, 95% CI 13.6%-15.6%). In cohort 1, a CCS of 1 or above yielded a sensitivity of 99.5% (95% CI 97.3%-99.9%). The sensitivity with an Ortho hs-cTnI cut-off of 1 ng/L or above was 91.2% (95% CI 86.5%-95.7%). The specificity of a CCS of 5 (97.8%, 95% CI 96.5%-98.7%) was higher than when the overall 99th-percentile cut-off for the Ortho hs-cTnI assay (> 11 ng/L; 90.1%, 95% CI 87.9%-92.0%) was used. A similar pattern was observed in cohort 2 at 30 days and persisted at 90 days with the Abbott hs-cTnI assay.

INTERPRETATION

The CCS derived with 2 different hs-cTnI assays and ED populations yielded higher sensitivity and specificity estimates for MACE than hs-cTnI alone. An intervention study is needed to evaluate the impact of the CCS at both the patient and hospital levels.

TRIAL REGISTRATION

ClinicalTrials.gov, no. NCT01994577.

Clinical evaluation of Ortho Clinical Diagnostics high-sensitivity cardiac Troponin I assay in patients with symptoms suggestive of acute coronary syndrome

BACKGROUND

As more companies obtain regulatory approval for high-sensitivity cardiac troponin (hs-cTn) assays there is an urgent need for independent analytical and clinical evaluations. To this end, we have evaluated Ortho Clinical Diagnostics' hs-cTnI assay and compared it to their contemporary cTnI-ES assay in emergency department (ED) patients with suspected acute coronary syndrome (ACS).

METHODS

The study cohort consisted of ED patients (n = 906) with symptoms suggestive of ACS who had Ortho hs-cTnI and cTnI-ES results at presentation and 3 h (with calculated delta (0-3 h) defined as the absolute concentration difference between paired results). The primary composite outcome was 7-day myocardial infarction (MI) or cardiovascular death, with secondary analyses performed for 7-day MI and index-MI. Analytical imprecision testing (i.e., coefficient of variation; CV), receiver-operating characteristic (ROC) curve analyses with area under the curve (AUC), and diagnostic parameters (sensitivity/specificity/predictive values) were calculated.

RESULTS

The hs-cTnI assay had superior precision compared to the cTnI-ES assay below 5 ng/L in EDTA plasma (hs-cTnI CV ≤ 15% versus cTnI-ES CV ≥ 85%). The AUCs were higher for hs-cTnI as compared to cTnI-ES at 0 h (0.88 vs. 0.85), 3 h (0.94 vs. 0.92), and the delta (0-3 h) value (0.91 vs. 0.85) for the primary composite outcome (p < 0.05). At 3 h, the sensitivity/specificity for index-MI was ≥97%/≥82%, for 7-day MI was ≥89%/≥84%, and for the primary composite outcome was ≥90%/≥85% using the manufacturer's sex-specific 99th-percentile cutoffs.

CONCLUSION

The Ortho hs-cTnI assay has superior analytical and clinical performance over their contemporary cTnI-ES assay in evaluating ED patients with symptoms suggestive of ACS.

A Multicenter Assessment of the Sensitivity and Specificity for a Single High-Sensitivity Cardiac Troponin Test at Emergency Department Presentation for Hospital Admission

Background

Studies have illustrated how a low or undetectable high-sensitivity cardiac troponin (hs-cTn) concentration at emergency department (ED) presentation can rule out myocardial infarction (MI). A problem with using an undetectable hs-cTn cutoff is that this value may be defined differently among hospitals and is also difficult to monitor. In the present study, we assess the diagnostic performance of a clinical chemistry score (CCS) vs hs-cTn alone in the presentation blood sample in the ED for patient hospital admission in a multicenter setting.

Methods

From January 1 to June 30, 2018, consecutive patients with random glucose, creatinine (for an estimated glomerular filtration rate calculation), and hs-cTnI (Abbott, 2 hospitals, Hamilton, Ontario, n = 10496) or hs-cTnT (Roche, 4 hospitals, Calgary, Alberta, n = 25177) were assessed for hospital admission with the CCS (range of scores, 0–5) or hs-cTn alone. Sensitivity, specificity, predicative values, and likelihood ratios were calculated for a CCS of 0 and 5 and for hs-cTn alone (hs-cTnI cutoffs, 5 and 26 ng/L; hs-cTnT cutoffs, 6 and 14 ng/L).

Results

The CCS of 0 (CCS &lt;1) identified approximately 10% of all patients as low risk and had a sensitivity for hospital admission of nearly 98% as compared to &lt;93% when hs-cTnT (&lt;6 ng/L) or hs-cTnI (&lt;5 ng/L) cutoffs alone were used. A CCS ≥5 had a specificity for hospital admission &gt;95%, with approximately 14% of patients at high risk.

Conclusions

An ED disposition (admit or send home) using the presentation blood sample could occur in nearly 25% of all patients by use of the CCS.

Analytical characterization of the Siemens Dimension EXL high-sensitivity cardiac troponin I assay

BACKGROUND

Siemens Healthcare Diagnostics has four commercially available assays on different analytical platforms using different methodologies to generate signal. We assessed the analytical performance of the Dimension EXL hs-cTnI assay (LOCI method) across different matrices and compared it to two different acridinium ester-based hs-cTnI assays (ADVIA Centaur and Abbott ARCHITECT).

METHODS

The analytical sensitivity and precision below the 99th-percentile was determined for the Dimension EXL hs-cTnI assay. Method comparisons were performed between the Dimension EXL contemporary cTnI and the hs-cTnI assays, between different matrices for the EXL hs-cTnI assay (serum, lithium heparin and EDTA plasma), and between different hs-cTnI assays (EXL versus ADVIA Centaur or Abbott ARCHITECT) using non-parametric analyses.

RESULTS

The limit of blank and detection were 0.9 ng/L and 1.7 ng/L, respectively, with imprecision of 5.8% at 8.6 ng/L and 3.2% at 47.5 ng/L. Comparison between the EXL contemporary cTnI and hs-cTnI assay (range: 2.6-4214 ng/L) yielded proportional lower concentrations for the hs-cTnI assay (slope = 0.86; 95%CI: 0.81 to 0.96, n = 40); however, there was no difference in concentrations below 100 ng/L between the assays (median difference = -2.7 ng/L; 95%CI: -9.8 to 9.3). Passing-Bablok regression analysis with EDTA plasma yielded proportionally higher concentrations with the EXL hs-cTnI versus Abbott hs-cTnI (slope = 1.45; 95%CI: 1.02-1.86, n = 40) with proportionally lower concentrations with EDTA versus lithium heparin plasma with the EXL hs-cTnI assay alone (slope = 0.93; 95%CI: 0.90 to 0.99, n = 40). Comparison with Abbott hs-cTnI concentrations below 100 ng/L in the three matrices, indicated that the EXL hs-cTnI assay yielded higher concentrations (median difference range: 3.4-9.4 ng/L), with differences also evident when comparing the EXL hs-cTnI assay to the ADVIA Centaur hs-cTnI assay.

CONCLUSION

The Siemens EXL hs-cTnI assay meets the analytical criteria for a high-sensitivity assay, with assay specific cutoffs important to maximize clinical performance.