Variability and Error in Cardiac Troponin Testing: An ACLPS Critical Review

Clinical Biochemistry of Serum Troponin

Accurate measurement and interpretation of serum levels of troponin (Tn) is a central part of the clinical workup of a patient presenting with chest pain suspicious for acute coronary syndrome (ACS). Knowledge of the molecular characteristics of the troponin complex and test characteristics of troponin measurement assays allows for a deeper understanding of causes of false positive and false negative test results in myocardial injury. In this review, we discuss the molecular structure and functions of the constituent proteins of the troponin complex (TnT, TnC, and TnI); review the different isoforms of Tn and where they are from; survey the evolution of clinical Tn assays, ranging from first-generation to high-sensitivity (hs); provide a primer on statistical interpretation of assay results based on different clinical settings; and discuss potential causes of false results. We also summarize the advances in technologies that may lead to the development of future Tn assays, including the development of point of care assays and wearable Tn sensors for real-time continuous measurement.

Rapid serum tubes reduce transport hemolysis and false positive rates for high-sensitivity troponin T

INTRODUCTION

Hemolysis in the emergency department (ED) can significantly delay results and appropriate action. We evaluated the main sources of hemolysis during sample collection, and to evaluate the use of rapid serum tubes (RST) as a transport hemolysis-mitigating measure for high-sensitivity troponin T (hs-cTnT) testing.

METHODS

We examined the effect of tube type, tube fill, types of sample draw and collection methods on hemolysis and hs-cTnT in samples (n = 158) from ED patients. We also compared hs-cTnT values in paired RST and plasma separate tube (PST) samples that were hemolysis-free.

RESULTS

The primary source of hemolysis in samples collected in the ED was underfilling tubes. In both tube types, PST and RST, filled tubes showed a median reduction in hemolysis of 69.1 % (p < 0.0001). Blood collected in RST also experienced less hemolysis compared to PST. In hemolysis-free samples, false positive results in PST were noted in patients with hs-cTnT values < 50 ng/l.

CONCLUSION

We suggest that proper tube filling during sample collection and use of RST tubes can significantly reduce the effects of hemolysis. In addition, laboratories should be aware that PST tubes have a non-trivial rate of false positives when hs-cTnT < 50 ng/l.

Diagnoses and Outcomes of Patients with Suspicion of Acute Coronary Syndrome and Raised High Sensitive Troponin I: A Single Center Study from Pakistan

Objectives  Troponins are classically raised in acute coronary syndrome (ACS) although other cardiovascular and non-cardiovascular causes are recognized. We aimed to see the association of high sensitivity (Hs) Troponin I values exceeding the sex-specific 99th percentile upper reference limit (URL) with diagnoses, emergency department (ED) outcomes, 30-day outcomes of admitted patients and predictors of ACS in both genders. Materials and Methods  A retrospective study of all patients presenting to the emergency department from January 2019 to April 2021 with suspicion of ACS and Hs-Troponin I values greater than the sex-specific 99th percentile URL. Statistical Analysis  SPSS version 24 was used, Pearson's chi-square tests, Fisher's exact test, Kruskal-Wallis test, Mann-Whitney U test, and odds ratios, including the 95% confidence intervals, for each characteristic were used for analysis. A p -value of < 0.05 was considered significant. Results  There were a total of 5,982 patients (3,031 males, 2,951 females), out of which 878 patients were admitted under the cardiology specialty. In patients who were admitted to the ward, mortality was higher in females (8.2%) with less than a 10-fold rise in Hs-Troponin I while similar in both genders (7.6%) in patients with Hs-troponin I greater than 10-fold of sex-specific 99th percentile URL. Raised low-density lipoprotein-cholesterol was a significant factor associated with 2.4 times higher odds of ACS. Conclusion  Women with Hs-Troponin values up to 10 times the URL, i.e., 15.6-160 ng/L have higher mortality than their male counterparts. LDL-cholesterol is a significant risk factor for ACS which should be controlled for its prevention.

The effect of the immunoassay curve fitting routine on bias in troponin

OBJECTIVES

Unlike many dose-response curves used in clinical chemistry, the immunoassay curve used to quantitate measurands is often sigmoidal rather than linear. Consequently, a more complex curve fitting model is required. Various models are available, but they can introduce bias, and there can be little awareness of why this error can be introduced.

CONTENT

These curve-fitting models include those based on the law of mass-action, empirical models such as splines or linearization models such as the log/logit function. All these models involve assumptions, which can introduce bias as the dose-response curve is 'forced' to fit or minimize the distance between the standard concentration points to the theoretical curve. The most common curve fitting model is the four or five parameter model, which uses four or five parameters to fit a sigmoidal curve to a set of standard points.

SUMMARY AND OUTLOOK

Measurement of cardiac troponin is an important element in establishing a diagnosis of acute myocardial infarction. We use troponin, a cardiac biomarker, to demonstrate the potential effect of the bias that the curve fit could introduce. Troponin is used for both rule-in and rule-out decisions at different concentrations and at either end of the dose-response curve. The curve fitting process can cause lot-to-lot reagent (and calibrator) variation in immunoassay. However, laboratory staff need to be aware of this potential source of error and why it occurs. Understanding how the error occurs leads to a greater awareness of the importance of validating new reagent/calibrator assessment using patient samples with concentrations at crucial decision points.

Autochthonous Babesia canis infections in 49 dogs in Germany

BACKGROUND

Vector-borne diseases are of increasing importance in Germany. Since 2015, autochthonous cases have been increasingly documented in Berlin/Brandenburg.

OBJECTIVES

Describe autochthonous Babesia canis infection in the Berlin/Brandenburg region.

ANIMALS

Forty-nine dogs with autochthonous B. canis infection.

METHODS

Evaluation of history, clinical signs, laboratory abnormalities, treatment, and outcome.

RESULTS

Dogs were presented between March and August (9) and September and January (40) in the years 2015-2021. Historical and clinical findings were lethargy (100%), pale mucous membranes (63%), fever (50%), and pigmenturia (52%). Common clinicopathological findings were thrombocytopenia (100%), anemia (85%), intravascular hemolysis (52%), pancytopenia (41%), and systemic inflammatory response syndrome (SIRS; 37%). Babesia detection was based on blood smear evaluation (n = 40) and PCR targeting the 18S rRNA gene of piroplasms (n = 49). Sequencing indicated 99.47% to 100% identity to B. canis sequences from GenBank. All dogs were treated with imidocarb (2.4-6.3 mg/kg; median, 5 mg/kg); 8 dogs received 1, 35 received 2, and 1 dog each received 3, 4, or 5 injections, respectively. Continued PCR-positive results were detected in 7 dogs after the 1st, in 5 after the 2nd, in 2 after the 3rd, and in 1 28 days after the 4th injection. Four dogs were euthanized and 3 dogs died.

CONCLUSIONS AND CLINICAL IMPORTANCE

Autochthonous B. canis infections in Berlin/Brandenburg were associated with severe clinicopathological changes, SIRS, and multiorgan involvement. Testing by PCR during and after treatment is advisable to monitor treatment success. Screening of blood donors in high-risk areas and year-round tick protection is strongly recommended.

Effect of Macrotroponin in a Cohort of Community Patients with Elevated Cardiac Troponin

BACKGROUND

Macrotroponin is an important cause of discrepancy between current high-sensitivity cardiac troponin (hs-cTn) assays, however, its clinical significance is unclear. This study examined the effects of macrotroponin and repeat testing by different hs-cTnI assays in a cohort of community patients with elevated hs-cTnI.

METHODS

The first residual serum specimen from each patient in the community admitted to hospital with elevated hs-cTnI (Siemens hs-cTnI Centaur) was retested after immunoglobulin depletion and by 5 other hs-cTn assays. Low recovery of cTnI (<40%) following immunoglobulin depletion was considered as macrotroponin. A retrospective chart review was performed for these participants. Investigator-adjudicated diagnosis served as the reference standard.

RESULTS

In our cohort of community patients with elevated troponin (n = 188), participants with macrotroponin (n = 99) often had a multifactorial or indeterminate myocardial injury (56% vs 25%) and were less likely to have acute coronary syndrome (9% vs 28%). On repeat testing of cTn on other platforms, better diagnostic performance (c-statistics) for ischemic and non-ischemic cardiac causes was observed on the Beckman Access hs-cTnI (0.74; 95% confidence interval [CI] 0.67-0.81) or the Abbott hs-cTnI Architect (0.75; CI 0.68-0.82) compared to the Siemens hs-cTnI Vista (0.62; CI 0.54-0.70; P < 0.05). This could be attributed to differences in assay reactivity for macrotroponin. Interestingly, better diagnostic performance was observed in patients without macrotroponin. Although a small number of deaths occurred (n = 16), participants with macrotroponin had better overall survival.

CONCLUSIONS

In the low-risk setting, the presence of macrotroponin was clinically associated with multifactorial or indeterminate causes of troponin elevation.

On the Effect of Heterophilic Antibodies on Serum Levels of Cardiac Troponins: A Brief Descriptive Review

Serum levels of cardiac troponins can be increased both with myocardial damage and in the absence of myocardial damage. In the second case, this is due to the influence of false-positive factors, among which heterophilic antibodies play a significant role. Understanding the causes of the formation of heterophilic antibodies, the features and mechanisms of their effect on serum levels of cardiac troponins, is an important condition for interpreting a false-positive result due to the influence of heterophilic antibodies. This brief, descriptive review presents the causes of heterophilic-antibodies formation and discusses their effect on serum levels of cardiac troponins.

High-Sensitivity Cardiac Troponin I Levels Below 99th Percentile Upper Reference Limit in Patients Presenting with Suspicion of Acute Coronary Syndrome (ACS) in Emergency Department at a Tertiary Care Hospital in Karachi, Pakistan

INTRODUCTION

Troponin I levels are biomarkers of choice for diagnosis of acute myocardial infarction (AMI). However, prognostic significance of values below the 99th percentile upper reference limit (URL) in patients presenting with symptoms suggestive of Acute coronary syndrome (ACS) need further evaluation.

AIM

The objectives of the study were to find the association of High sensitivity (hs)-Troponin I values below 99th percentile URL with age and the Emergency Department (ED) outcome, to determine single cut-off for safe discharge of these patients from the ED and to determine the 30-day outcome of the patients admitted under cardiac speciality.

METHODS

This is a retrospective study of patients presenting with suspicion of ACS in the ED between January 2019 till April 2021 and hs-Troponin I values below 99th percentile URL.

RESULTS

Among 15,441 patients, 8034 (52%) were males and 7407 (48%) were females. 9677 (63%) of the patients had hs-Troponin I values < 5 ng/L while 5764 (37%) had values between 5 ng/L and 99th percentile URL. Higher hs-Troponin I values were associated with a worse ED outcome. Serial troponin I levels were performed in only 2.4% of the cohort. Receiver operating characteristics for ACS demonstrated an AUC of 0.84 at a cut off value of 12.75 ng/L, with sensitivity (76.9%) and specificity was 75.1%. The 30-day outcome of the patients admitted under cardiac speciality revealed no mortality in either group.

CONCLUSION

An overall single cut-off value of 12.75 ng/L can be used in our population for ruling our ACS provided it is unaccompanied by other supportive clinical and ECG findings.

Skeletal Muscle Disorders: A Noncardiac Source of Cardiac Troponin T

BACKGROUND

Cardiac troponin (cTn) T and cTnI are considered cardiac specific and equivalent in the diagnosis of acute myocardial infarction. Previous studies suggested rare skeletal myopathies as a noncardiac source of cTnT. We aimed to confirm the reliability/cardiac specificity of cTnT in patients with various skeletal muscle disorders (SMDs).

METHODS

We prospectively enrolled patients presenting with muscular complaints (≥2 weeks) for elective evaluation in 4 hospitals in 2 countries. After a cardiac workup, patients were adjudicated into 3 predefined cardiac disease categories. Concentrations of cTnT/I and resulting cTnT/I mismatches were assessed with high-sensitivity (hs-) cTnT (hs-cTnT-Elecsys) and 3 hs-cTnI assays (hs-cTnI-Architect, hs-cTnI-Access, hs-cTnI-Vista) and compared with those of control subjects without SMD presenting with adjudicated noncardiac chest pain to the emergency department (n=3508; mean age, 55 years; 37% female). In patients with available skeletal muscle biopsies, TNNT/I1-3 mRNA differential gene expression was compared with biopsies obtained in control subjects without SMD.

RESULTS

Among 211 patients (mean age, 57 years; 42% female), 108 (51%) were adjudicated to having no cardiac disease, 44 (21%) to having mild disease, and 59 (28%) to having severe cardiac disease. hs-cTnT/I concentrations significantly increased from patients with no to those with mild and severe cardiac disease for all assays (all P<0.001). hs-cTnT-Elecsys concentrations were significantly higher in patients with SMD versus control subjects (median, 16 ng/L [interquartile range (IQR), 7-32.5 ng/L] versus 5 ng/L [IQR, 3-9 ng/L]; P<0.001), whereas hs-cTnI concentrations were mostly similar (hs-cTnI-Architect, 2.5 ng/L [IQR, 1.2-6.2 ng/L] versus 2.9 ng/L [IQR, 1.8-5.0 ng/L]; hs-cTnI-Access, 3.3 ng/L [IQR, 2.4-6.1 ng/L] versus 2.7 ng/L [IQR, 1.6-5.0 ng/L]; and hs-cTnI-Vista, 7.4 ng/L [IQR, 5.2-13.4 ng/L] versus 7.5 ng/L [IQR, 6-10 ng/L]). hs-cTnT-Elecsys concentrations were above the upper limit of normal in 55% of patients with SMD versus 13% of control subjects (P<0.01). mRNA analyses in skeletal muscle biopsies (n=33), mostly (n=24) from individuals with noninflammatory myopathy and myositis, showed 8-fold upregulation of TNNT2, encoding cTnT (but none for TNNI3, encoding cTnI) versus control subjects (n=16, P_Wald<0.001); the expression correlated with pathological disease activity (R=0.59, P_t-statistic<0.001) and circulating hs-cTnT concentrations (R=0.26, P_t-statistic=0.031).

CONCLUSIONS

In patients with active chronic SMD, elevations in cTnT concentrations are common and not attributable to cardiac disease in the majority. This was not observed for cTnI and may be explained in part by re-expression of cTnT in skeletal muscle.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT03660969.

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.

Effect of Particle Size and Surface Chemistry of Photon-Upconversion Nanoparticles on Analog and Digital Immunoassays for Cardiac Troponin

Sensitive immunoassays are required for troponin, a low-abundance cardiac biomarker in blood. In contrast to conventional (analog) assays that measure the integrated signal of thousands of molecules, digital assays are based on counting individual biomarker molecules. Photon-upconversion nanoparticles (UCNP) are an excellent nanomaterial for labeling and detecting single biomarker molecules because their unique anti-Stokes emission avoids optical interference, and single nanoparticles can be reliably distinguished from the background signal. Here, the effect of the surface architecture and size of UCNP labels on the performance of upconversion-linked immunosorbent assays (ULISA) is critically assessed. The size, brightness, and surface architecture of UCNP labels are more important for measuring low troponin concentrations in human plasma than changing from an analog to a digital detection mode. Both detection modes result approximately in the same assay sensitivity, reaching a limit of detection (LOD) of 10 pg mL^-1 in plasma, which is in the range of troponin concentrations found in the blood of healthy individuals.

Cardiac troponin I and the risk of cardiovascular or non-cardiovascular death in patients visiting the emergency department

The prognostic implication of cardiac troponin I (cTnI) values for the determination of the magnitude or duration of cause-specific death risk is limited. We included consecutive patients with maximal cTnI values within 24 h of their emergency department visits. Multivariate analyses using variables selected by the Bayesian information criterion were performed to investigate the impact of cTnI on the event rate, time-dependent risk, and dose-dependent risk of cardiovascular or non-cardiovascular death within 360 days. There were 5472 (14.9%) all-cause deaths including 881 (2.4%) cardiovascular deaths and 4591 (12.5%) non-cardiovascular deaths. In patients with positive cTnI, defined as the ≥ 99th percentile of the upper normal limit, the cumulative risk of cardiac and non-cardiac death was 4.4- and 1.4-fold higher, respectively, than that of negative cTnI, respectively. In the competing risk analysis, positive cTnI was linked to 2.4- and 1.2-fold higher risks of cardiovascular and non-cardiovascular death, respectively. The cTnI value showed a positive relationship with the risk of both cardiovascular and non-cardiovascular deaths. In the time-dependent risk analysis, the excess risk of cardiovascular death was mostly evident in the first few weeks. Higher cTnI value was associated with an increased risk of both cardiovascular and non-cardiovascular death, especially which was in the early period.

Short- and long-term biological variation of cardiac troponin I in healthy individuals, and patients with end-stage renal failure requiring haemodialysis or cardiomyopathy

Objectives High-sensitivity (hs) cardiac troponin (cTn) assays can quantitate small fluctuations in cTn concentration. Determining biological variation allows calculation of reference change values (RCV), to define significant changes. We assessed the short- and long-term biological variation of cardiac troponin I (cTnI) in healthy individuals and patients with renal failure requiring haemodialysis or cardiomyopathy. Methods Plasma samples were collected hourly for 4 h and weekly for seven further weeks from 20 healthy individuals, 9 renal failure patients and 20 cardiomyopathy patients. Pre- and post-haemodialysis samples were collected weekly for 7 weeks. Samples were analysed using a hs-cTnI assay (Abbott Alinity ci-series). Within-subject biological variation (CVI), analytical variation (CVA) and between-subject biological variation (CVG) was used to calculate RCVs and index of individuality (II). Results For healthy individuals, CVI, CVA, CVG, RCV and II values were 8.8, 14.0, 43.1, 45.8% and 0.38 respectively for short-term, and 41.4, 14.0, 25.8, 121.0% and 1.69 for long-term. For renal failure patients, these were 2.6, 5.8, 50.5, 17.6% and 0.30 respectively for short-term, and 19.1, 5.8, 11.2, 55.2% and 1.78 for long-term. For cardiomyopathy patients, these were 4.2, 10.0, 65.9, 30.0% and 0.16 respectively for short-term, and 17.5, 10.0, 63.1, 55.8% and 0.32 for long-term. Mean cTnI concentration was lower post-haemodialysis (15.2 vs. 17.8 ng/L, p < 0.0001), with a 16.9% mean relative change. Conclusions The biological variation of cTnI is similar between end-stage renal failure and cardiomyopathy patients, but proportionately greater in well-selected healthy individuals with very low baseline cTnI concentrations.

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.

Persistent Troponin Elevation in the Setting of an Elevated Rheumatoid Factor: When It Pays to Double Check

A 78-year-old woman presented twice with high sensitivity troponin I (hs-TnI) elevation. Two cardiac catheterizations showed nonocclusive coronary artery disease, and 2 cardiac magnetic resonance imaging scans were normal. With these investigations unable to explain the troponin I (hs-TnI) elevation, alternate troponin samples were sent to check for assay interference. Results from these troponin assays were low. With the patient having elevated rheumatoid factor as a potential contributor to assay interference, the lab reanalyzed the samples using heterophile antibody blocking tubes, revealing lower hs-TnI levels. This case serves as a reminder to consider assay interference when the clinical picture is inconsistent with ischemia.

Network of gold conjugates for enhanced sensitive immunochromatographic assays of troponins

Highly sensitive detection of cardiac troponins I and T (cTnI and cTnT) was completed by immunochromatography with double amplification, through the binding of functionalized gold nanoparticles (GNPs). The robust nature of the approach, based on the formation of nanoparticle networks through the biotin-streptavidin interaction, was confirmed; the choice of the best assay parameters for maximal increase in ICA sensitivity was demonstrated. A bifunctional conjugate of GNPs with biotinylated specific IgG and two auxiliary conjugates, GNP-biotin and GNP-streptavidin, form three-component aggregates in the analytical zone of the test strip. The inclusion of abundant gold labels in the resulting immune complex leads to an amplified colorimetric signal. The limits of detection (LoDs) of cTnI and cTnT were 0.9 and 0.4 ng mL-1, respectively, which is 3 times lower than the LoDs of more commonly used systems. Visual LoDs were 10-fold lower in concentration. The enhancement has been realized both in single and double assay formats; analysis of cTnI and cTnT presented the same characteristics.

Disagreement between Cardiac Troponin Tests Yielding a Higher Incidence of Myocardial Injury in the Emergency Setting

Differences in patient classification of myocardial injury between high-sensitivity cardiac troponin (hs-cTn) assays have largely been attributed to assay design and analytical sensitivity aspects. Our objective was to compare Ortho Clinical Diagnostics' (OCD) hs-cTnI assay to OCD's contemporary/conventional assay (cTnI ES) and another hs-cTnI assay (Abbott hs-cTnI) in samples obtained from different emergency departments (EDs). Two different sample types were evaluated (lithium heparin and ethylenediaminetetraacetic acid (EDTA) plasma) in a non-selected ED population (study 1, n = 469 samples) and in patients for which ED physicians ordered cardiac troponin testing (study 2, n = 1147 samples), from five different EDs. The incidence of injury in study 1 was higher with the OCD hs-cTnI assay (30.9%; 95% CI: 26.9 to 35.2) compared to that of the Abbott hs-cTnI (17.3%; 95% CI: 14.1 to 21.0) and the OCD cTnI ES (15.4%; 95% CI: 12.4 to 18.9) assays, with repeat testing identifying 4.8% (95% CI: 3.0 to 7.5) of the OCD hs-cTnI results with poor reproducibility. In study 2, 4.6% (95% CI: 3.5 to 6.0) of the results were not reported for the OCD hs-cTnI assay (i.e., poor reproducibility) with 12.7% (95%CI: 8.7 to 17.8) of the OCD hs-cTnI results positive for injury being negative for injury with the Abbott hs-cTnI assay. In summary, the OCD hs-cTnI assay yields higher rates of biochemical injury with a higher rate of poor reproducible results in different ED populations.

Effect of type of diet on blood and plasma taurine concentrations, cardiac biomarkers, and echocardiograms in 4 dog breeds

Background

Associations of diet with dilated cardiomyopathy are under investigation.

Objectives

That cardiac assessment would show abnormalities in healthy dogs eating grain‐free (GF) diets or diets with Food and Drug Administration (FDA)‐listed ingredients of concern (peas, lentils, or potatoes) as top 10 ingredients (FDA‐PLP), but not in dogs eating grain‐inclusive (GI) diets or diets without FDA‐listed ingredients of concern (PLP) in the top 10 ingredients (NoFDA‐PLP).

Animals

One hundred eighty‐eight healthy Doberman Pinschers, Golden Retrievers, Miniature Schnauzers, and Whippets.

Methods

This study was an observational cross‐sectional study. Echocardiograms, cardiac biomarkers, and blood and plasma taurine concentrations were compared between dogs eating GF (n = 26) and GI (n = 162) diets, and between FDA‐PLP (n = 39) and NoFDA‐PLP (n = 149) diets, controlling for age and breed. Demographic characteristics, murmurs, genetic status, and ventricular premature complexes (VPCs) during examination were compared between dogs eating different diet types.

Results

No differences in echocardiographic variables, N‐terminal pro‐B‐type natriuretic peptide or whole blood taurine were noted between dogs eating different diet types. Dogs eating GF diets had higher median high‐sensitivity cardiac troponin I (hs‐cTnI) (GF 0.076 ng/mL [Interquartile range (IQR), 0.028‐0.156] vs. GI 0.048 [IQR, 0.0026‐0.080]; P < .001) and higher median plasma taurine (GF 125 nmol/mL [IQR, 101‐148] vs GI 104 [IQR, 86‐123]; P = .02) than dogs eating GI diets. Dogs eating FDA‐PLP diets had higher median hs‐cTnI (0.059 ng/mL [IQR, 0.028‐0.122]) than dogs eating NoFDA‐PLP diets (0.048 [IQR, 0.025‐0.085]; P = .006). A greater proportion of dogs eating FDA‐PLP diets (10%) had VPCs than dogs eating NoFDA‐PLP diets (2%; P = .04).

Conclusions and Clinical Importance

Higher hs‐cTnI in healthy dogs eating GF and FDA‐PLP diets might indicate low‐level cardiomyocyte injury.

Gradient-Based Rapid Digital Immunoassay for High-Sensitivity Cardiac Troponin T (hs-cTnT) Detection in 1 μL Plasma

Rapid and sensitive detection of biomarkers is the key to the diagnosis of acute diseases. One example is the detection of troponin in myocardial infarction. Here, we report a gradient-based digital immunoassay method, which can achieve high-sensitivity cardiac troponin T (hs-cTnT) detection with only 1 μL of plasma sample. We designed a multizone microfluidic channel functionalized with capture antibody specific to troponin. Taking advantage of limited sample volume, a troponin concentration gradient is created along the channel because of binding induced depletion. We quantified the concentration gradient by counting the detection antibody conjugated gold nanoparticles bound to different test zones with optical imaging. Differential counting between the zones removes most common noises and nonspecific bindings. The total analytical time is about 30 min, and the limit of quantification is 6.2 ng/L. We examined 41 clinical plasma samples from 15 patients and the change in hs-cTnT concentration in serial samples showed good linear correlation with clinical results (R² = 0.98). Therefore, this simple and sensitive gradient-based digital immunoassay method is a promising technology for clinical hs-cTnT detection and could be adapted for detection of other biomarkers.

The underestimated issue of non-reproducible cardiac troponin I and T results: case series and systematic review of the literature

Cardiac troponins (cTn) are the preferred biomarkers for the evaluation of myocardial injury and play a key role in the diagnosis of acute myocardial infarction (MI). Pre-analytical or analytical issues and interferences affecting troponin T and I assays are therefore of major concern given the risk of misdiagnosis. False positive troponin results have been related to various interferences including anti-troponin antibodies, heterophilic antibodies, or elevated alkaline phosphatase level. On the other hand, false negative results have been reported in the case of a large biotin intake. These interferences are characterized with erroneous but reproducible troponin results. Of interest, non-reproducible results have also been reported in the literature. In other words, if the sample is reanalyzed a second time, a significant difference in troponin results will be observed. These interferences have been named "fliers" or "outliers". Compared to the biotin interference that received major attention in the literature, troponin outliers are also able to induce harmful clinical consequences for the patient. Moreover, the prevalence of outliers in recent studies was found to be higher (0.28-0.57%) compared to the biotin interference. The aim of this systematic review is to warn clinicians about these non-reproducible results that may alter their clinical judgment. Four case reports that occurred in the Clinique of Saint-Luc Bouge are presented to attest this point. Moreover, we aimed at identifying the nature of these non-reproducible troponin results, determining their occurrence, and describing the best way for their identification.

Recent advances in cardiac biomarkers detection: From commercial devices to emerging technologies

Although cardiac pathologies are the major cause of death in the world, it remains difficult to provide a reliable diagnosis to prevent heart attacks. Rapid patient care and management in emergencies are critical to prevent dramatic consequences. Thus, relevant biomarkers such as cardiac troponin and natriuretic peptides are currently targeted by commercialized Point-Of-Care immunoassays. Key points still to be addressed concern cost, lack of standardization, and poor specificity, which could limit the reliability of the assays. Consequently, alternatives are emerging to address these issues. New probe molecules such as aptamers or molecularly imprinted polymers should allow a reduction in cost of the assays and an increase in reproducibility. In addition, the assay specificity and reliability could be improved by enabling multiplexing through the detection of several molecular targets in a single device.

Evaluating the performance of an updated high-sensitivity troponin T assay with increased tolerance to biotin

OBJECTIVES

Biotin >20 ng/mL may interfere with the Elecsys^® Troponin T-high sensitive assay (cTnT-hs; Roche Diagnostics International Ltd). We evaluated the performance of an updated assay, cTnT-hs*, which was designed to reduce biotin interference.

METHODS

cTnT-hs* assay performance was assessed using up to two applications (18 min/9 min) on three analyzers (cobas e 411/cobas e 601/cobas e 801). Biotin interference was determined by measuring recovery in an 11-sample series dilution with biotin ranging from 0-3600 ng/mL. Repeatability/reproducibility were evaluated in five serum sample pools (n=75 each). Method comparisons tested: cTnT-hs* vs. cTnT-hs (18 min/cobas e 601); cTnT-hs* assay 18 vs. 9 min (cobas e 601); cTnT-hs* (18 min) on cobas e 601 vs. cobas e 411 and cobas e 601 vs. cobas e 801. Concordance at the 99th percentile decision limit between cTnT-hs* and cTnT-hs (9 min/cobas e 601) was calculated using 300 lithium-heparin plasma samples and a 14 ng/L assay cutoff.

RESULTS

cTnT-hs* assay (18 min/cobas e 601) recovery was ≥96% for biotin ≤1250 ng/mL. Across all applications/analyzers, coefficients of variation for repeatability/reproducibility with the cTnT-hs* assay were <5% in most serum sample pools (mean cardiac troponin T: 8.528-9484 ng/L). High correlation (Pearson's r=1.000) was demonstrated for all method comparisons. Concordance at the 99th percentile decision limit was high between the cTnT-hs* and cTnT-hs assays.

CONCLUSIONS

The updated cTnT-hs* assay may provide greater tolerance to biotin interference, and shows good analytical and clinical agreement/concordance with the previous cTnT-hs assay.

Benefits of Home-Based Solutions for Diagnosis and Treatment of Acute Coronary Syndromes on Health Care Costs: A Systematic Review

Diagnosing and treating acute coronary syndromes consumes a significant fraction of the healthcare budget worldwide. The pressure on resources is expected to increase with the continuing rise of cardiovascular disease, other chronic diseases and extended life expectancy, while expenditure is constrained. The objective of this review is to assess if home-based solutions for measuring chemical cardiac biomarkers can mitigate or reduce the continued rise in the costs of ACS treatment. A systematic review was performed considering published literature in several relevant public databases (i.e., PUBMED, Cochrane, Embase and Scopus) focusing on current biomarker practices in high-risk patients, their cost-effectiveness and the clinical evidence and feasibility of implementation. Out of 26,000 references screened, 86 met the inclusion criteria after independent full-text review. Current clinical evidence highlights that home-based solutions implemented in primary and secondary prevention reduce health care costs by earlier diagnosis, improved patient outcomes and quality of life, as well as by avoidance of unnecessary use of resources. Economical evidence suggests their potential to reduce health care costs if the incremental cost-effectiveness ratio or the willingness-to-pay does not surpass £20,000/QALY or €50,000 limit per 20,000 patients, respectively. The cost-effectiveness of these solutions increases when applied to high-risk patients.

Biosensing based on surface-enhanced Raman spectroscopy as an emerging/next-generation point-of-care approach for acute myocardial infarction diagnosis

Cardiovascular disease is a major global health issue. In particular, acute myocardial infarction (AMI) requires urgent attention and early diagnosis. The use of point-of-care diagnostics has resulted in the improved management of cardiovascular disease, but a major drawback is that the performance of POC devices does not rival that of central laboratory tests. Recently, many studies and advances have been made in the field of surface-enhanced Raman scattering (SERS), including the development of POC biosensors that utilize this detection method. Here, we present a review of the strengths and limitations of these emerging SERS-based biosensors for AMI diagnosis. The ability of SERS to multiplex sensing against existing POC detection methods are compared and discussed. Furthermore, SERS calibration-free methods that have recently been explored to minimize the inconvenience and eliminate the limitations caused by the limited linear range and interassay differences found in the calibration curves are outlined. In addition, the incorporation of artificial intelligence (AI) in SERS techniques to promote multivariate analysis and enhance diagnostic accuracy are discussed. The future prospects for SERS-based POC devices that include wearable POC SERS devices toward predictive, personalized medicine following the Fourth Industrial Revolution are proposed.

Nanoproteomics enables proteoform-resolved analysis of low-abundance proteins in human serum

Top-down mass spectrometry (MS)-based proteomics provides a comprehensive analysis of proteoforms to achieve a proteome-wide understanding of protein functions. However, the MS detection of low-abundance proteins from blood remains an unsolved challenge due to the extraordinary dynamic range of the blood proteome. Here, we develop an integrated nanoproteomics method coupling peptide-functionalized superparamagnetic nanoparticles (NPs) with top-down MS for the enrichment and comprehensive analysis of cardiac troponin I (cTnI), a gold-standard cardiac biomarker, directly from serum. These NPs enable the sensitive enrichment of cTnI (<1 ng/mL) with high specificity and reproducibility, while simultaneously depleting highly abundant proteins such as human serum albumin (>1010 more abundant than cTnI). We demonstrate that top-down nanoproteomics can provide high-resolution proteoform-resolved molecular fingerprints of diverse cTnI proteoforms to establish proteoform-pathophysiology relationships. This scalable and reproducible antibody-free strategy can generally enable the proteoform-resolved analysis of low-abundance proteins directly from serum to reveal previously unachievable molecular details.

Paper/Soluble Polymer Hybrid-Based Lateral Flow Biosensing Platform for High-Performance Point-of-Care Testing

As a global shift continues to occur in high burden diseases toward developing countries, the importance of medical diagnostics based on point-of-care testing (POCT) is rapidly increasing. However, most diagnostic tests that meet clinical standards rely on high-end analyzers in central hospitals. Here, we report the development of a simple, low-cost, mass-producible, highly sensitive/quantitative, automated, and robust paper/soluble polymer hybrid-based lateral flow biosensing platform, paired with a smartphone-based reader, for high-performance POCT. The testing architecture incorporates a polymeric barrier that programs/automates sequential reactions via a polymer dissolving mechanism. The smartphone-based reader with simple opto-mechanical parts offers a stable framework for accurate quantification. Analytical performance of this platform was evaluated by testing human cardiac troponin I (cTnI), a preferred biomarker for the diagnosis of myocardial infarction, in serum/plasma samples. Coupled with catalytic/colorimetric gold-ion amplification, this platform produced results within 20 min with a detection limit of 0.92 pg mL^-1 and a coefficient of variation <10%, which is equivalent to the performance of a high-sensitivity standard analyzer, and operated within acceptable levels stipulated by clinical guidelines. Moreover, cTnI clinical sample tests indicate a high correlation (r = 0.981) with the contemporary analyzers, demonstrating the clinical utility of this platform in high-performance POCT.

One-Step Digital Immunoassay for Rapid and Sensitive Detection of Cardiac Troponin I

A rapid and sensitive method to detect cardiac troponin I (cTnI) in human blood is critical to the diagnosis and treatment of acute myocardial infarction (AMI). Here, we describe a simple one-step digital immunoassay for single-molecule detection without washing steps. A sample containing cTnI mixed with detection antibody-conjugated gold nanoparticles (AuNPs) is added to a capture antibody-coated sensor surface and the formation of the antibody-cTnI-antibody sandwich is detected by digitally counting the binding of the individual gold nanoparticles to the sensor surface in real time using a bright-field optical imaging setup together with a differential imaging algorithm. The digital immunoassay detects cTnI in undiluted human plasma, which achieves a detection limit of 5.7 ng/L within a detection time of only 10 min, which meets the requirement of current clinical high-sensitivity troponin assay (∼70 ng/L cutoff). We anticipate that the one-step and real-time digital immunoassay can be applied to the detection of other disease biomarkers in blood.

Safety and efficacy of the European Society of Cardiology 0/1-hour algorithm for diagnosis of myocardial infarction: systematic review and meta-analysis

OBJECTIVE

The European Society of Cardiology (ESC) 0/1 hour algorithm has been primarily validated in Europe, America and Australasia with less knowledge of its performance outside of these settings. We aim to evaluate the performance of the ESC 0/1 hour algorithm across different contexts.

METHODS

We searched PubMed, Embase, Scopus, Web of Science and the Cochrane Central Register of Controlled Trials for relevant studies published between 1 January 2008 and 31 May 2019. The primary outcome was index myocardial infarction and the secondary outcome was major adverse cardiac event or mortality. A bivariate random-effects meta-analysis was used to derive the pooled estimate of each outcome.

RESULTS

A total of 11 014 patients from 10 cohorts were analysed for the primary outcome. The algorithm based on high-sensitivity cardiac troponin (hs-cTn)T (Roche), hs-cTnI (Abbott) and hs-cTnI (Siemens) had pooled sensitivity of 98.4% (95% CI=95.1% to 99.5%), 98.1% (95% CI=94.6% to 99.3%) and 98.7% (95% CI=97.3% to 99.3%), respectively. The algorithm based on hs-cTnT (Roche) and hs-cTnI (Siemens) had pooled specificity of 91.2% (95% CI=86.0% to 94.6%) and 95.9% (95% CI=94.1% to 97.2%), respectively. Among patients in the rule-out category, the pooled mortality rate at 30 days and at 1 year was 0.1% (95% CI=0.0% to 0.4%) and 0.8% (95% CI=0.5% to 1.2%), respectively. Among patients in the observation zone, the pooled mortality rate was 0.7% (95% CI=0.3% to 1.2%) at 30 days but increased to 8.1% (95% CI=6.1% to 10.4%) at 1 year, comparable to the mortality rate in the rule-in group.

CONCLUSION

The ESC 0/1 hour algorithm has high diagnostic accuracy but may not be sufficiently safe if the 1% miss-rate for myocardial infarction is desired.

PROSPERO REGISTRATION NUMBER

CRD42019142280.

MicroRNAs as potential biomarkers in congenital heart surgery

OBJECTIVE

Pediatric congenital heart surgery (CHS) involves intracardiac, valvular, and vascular repairs. Accurate tools to aid short-term outcome prediction in pediatric CHS are lacking. Clinical scores, such as the vasoactive-inotrope score and ventilation index, are used to define outcome in clinical studies. MicroRNA-1-3p (miR-1) is expressed by both cardiomyocytes and vascular cells and is regulated by hypoxia. In adult patients, miR-1 increases in the circulation after open-heart cardiac surgery, suggesting its potential as a clinical biomarker. Thus, we investigated whether perioperative circulating miR-1 measurements can help predict post-CHS short-term outcomes in pediatric patients.

METHODS

Plasma miR-1 was retrospectively measured in a cohort of 199 consecutive pediatric CHS patients (median age 1.2 years). Samples were taken before surgery and at the end of the operation. Plasma miR-1 concentration was measured by reverse transcription-quantitative polymerase chain reaction and expressed as miR-1 copies/μL and as relative expression to spiked-in exogenous cel-miR-39.

RESULTS

Baseline plasma miR-1 did not vary across different diagnoses, increased during surgery (204-fold median relative increase, P < .001), and was associated with aortic crossclamp duration postoperatively (P < .001). Importantly, miR-1 levels at the end of the operation positively correlated with intensive care stay (P < .001), early severe cardiovascular events (P = .01), and with high vasoactive-inotrope score (P = .001) and ventilation index (P < .001), suggesting that miR-1 could accelerate the identification of patients with cardiopulmonary bypass-related ischemic complications, requiring more intensive support.

CONCLUSIONS

Our study suggests miR-1 as a novel potential circulating biomarker to predict early postoperative outcome and inform clinical management in pediatric heart surgery.

Early kinetic profiles of troponin I and T measured by high-sensitivity assays in patients with myocardial infarction

The early concentration kinetic profiles of cardiac troponin in patients with non-ST-elevated myocardial infarction (NSTEMI) measured by high-sensitivity cardiac troponin I (hs-cTnI) and T (hs-cTnT) assays have not been described. In intermediate-to-high-risk of NSTEMI patients we measured serial cTn concentrations on ED arrival, at 1, 2, 3, 6-12, 24 and 48-hours with hs-cTnI and hs-cTnT assays. Log-normal curves were fitted to concentrations from time from symptom onset, and the time to rule-out decision thresholds estimated (hs-cTnI: 2 ng/L and 5 ng/L; hs-cTnT: 5 ng/L). Among 164 patients there were 58 NSTEMI. The hs-cTnI to hs-cTnT ratio increased linearly over the first 6-12 h following symptom onset. The estimated times from symptom onset to the 2 ng/L and 5 ng/L thresholds for hs-cTnI were 1.8 (0.1-3.1) and 1.9 (1.1-3.5) hours, and to the 5 ng/L threshold for hs-cTnT 1.9 (1.1-3.8) hours. The estimated time to exceed 5 ng/L was ≥3 hours in 32.6% (95%CI: 20.0% to 48.1%) cases for hs-cTnI and 33.3% (19.6% to 50.0%) for hs-cTnT. cTnI concentrations increased at a much more rapid rate than cTnT concentrations in patients with NSTEMI. Concentrations of a high proportion of patients took longer than 3 hours from symptom onset to exceed the 5 ng/L rule-out decision threshold.

Nanoscale Technologies for Prevention and Treatment of Heart Failure: Challenges and Opportunities

The adult myocardium has a limited regenerative capacity following heart injury, and the lost cells are primarily replaced by fibrotic scar tissue. Suboptimal efficiency of current clinical therapies to resurrect the infarcted heart results in injured heart enlargement and remodeling to maintain its physiological functions. These remodeling processes ultimately leads to ischemic cardiomyopathy and heart failure (HF). Recent therapeutic approaches (e.g., regenerative and nanomedicine) have shown promise to prevent HF postmyocardial infarction in animal models. However, these preclinical, clinical, and technological advancements have yet to yield substantial enhancements in the survival rate and quality of life of patients with severe ischemic injuries. This could be attributed largely to the considerable gap in knowledge between clinicians and nanobioengineers. Development of highly effective cardiac regenerative therapies requires connecting and coordinating multiple fields, including cardiology, cellular and molecular biology, biochemistry and chemistry, and mechanical and materials sciences, among others. This review is particularly intended to bridge the knowledge gap between cardiologists and regenerative nanomedicine experts. Establishing this multidisciplinary knowledge base may help pave the way for developing novel, safer, and more effective approaches that will enable the medical community to reduce morbidity and mortality in HF patients.

High-sensitivity troponin assays: development and utility in a modern health-care system

Introduction: The introduction of cardiac troponin (cTn) assays have revolutionized the diagnosis and management of acute myocardial infarction in Emergency Departments worldwide. Its success has led to significant research and development investment in this area culminating in the development of newer high-sensitivity cardiac troponin assays (hs-cTn). While these newer assays allow for more rapid diagnosis by decreasing the time interval between serial data points, there is an inevitable trade off between increasing sensitivity and specificity. This review examines in detail the introduction and implementation of hs-cTN and its implications for clinical practice.Areas covered: This article reviews the history and development of high-sensitivity troponin assays and their application to clinical practice and current evidence base. It also discusses both the positive and negative aspects of the continuing increasing sensitivity of biochemical assays and the translation of this into clinical practice. Potential future developments are also discussed.Expert commentary: It is clear that there are many benefits to detecting extremely low concentration of cardiac troponin including the development of rapid rule out algorithms and the cost and time-saving advantages associated with the quicker movement of patients through the health-care system. It is important to note however that detecting troponin at very low concentrations also dramatically increases the false-positive rates and leads to a potentially large increase in invasive testing and diagnosis of myocardial infarction.

Clinical chemistry score versus high-sensitivity cardiac troponin I and T tests alone to identify patients at low or high risk for myocardial infarction or death at presentation to the emergency department

BACKGROUND

Testing for high-sensitivity cardiac troponin (hs-cTn) may assist triage and clinical decision-making in patients presenting to the emergency department with symptoms of acute coronary syndrome; however, this could result in the misclassification of risk because of analytical variation or laboratory error. We sought to evaluate a new laboratory-based risk-stratification tool that incorporates tests for hs-cTn, glucose level and estimated glomerular filtration rate to identify patients at risk of myocardial infarction or death when presenting to the emergency department.

METHODS

We constructed the clinical chemistry score (CCS) (range 0-5 points) and validated it as a predictor of 30-day myocardial infarction (MI) or death using data from 4 cohort studies involving patients who presented to the emergency department with symptoms suggestive of acute coronary syndrome. We calculated diagnostic parameters for the CCS score separately using high-sensitivity cardiac troponin I (hs-cTnI) and high-sensitivity cardiac troponin T (hs-cTnT).

RESULTS

For the combined cohorts (n = 4245), 17.1% of participants had an MI or died within 30 days. A CCS score of 0 points best identified low-risk participants: the hs-cTnI CCS had a sensitivity of 100% (95% confidence interval [CI] 99.5%-100%), with 8.9% (95% CI 8.1%-9.8%) of the population classified as being at low risk of MI or death within 30 days; the hs-cTnT CCS had a sensitivity of 99.9% (95% CI 99.2%-100%), with 10.5% (95% CI 9.6%-11.4%) of the population classified as being at low risk. The CCS had better sensitivity than hs-cTn alone (hs-cTnI < 5 ng/L: 96.6%, 95% CI 95.0%-97.8%; hs-cTnT < 6 ng/L: 98.2%, 95% CI 97.0%-99.0%). A CCS score of 5 points best identified patients at high risk (hs-cTnI CCS: specificity 96.6%, 95% CI 96.0%-97.2%; 11.2% [95% CI 10.3%-12.2%] of the population classified as being at high risk; hs-cTnT CCS: specificity 94.0%, 95% CI 93.1%-94.7%; 13.1% [95% CI 12.1%-14.1%] of the population classified as being at high risk) compared with using the overall 99th percentiles for the hs-cTn assays (specificity of hs-cTnI 93.2%, 95% CI 92.3-94.0; specificity of hs-cTnT 73.8%, 95% CI 72.3-75.2).

INTERPRETATION

The CCS score at the chosen cut-offs was more sensitive and specific than hs-cTn alone for risk stratification of patients presenting to the emergency department with suspected acute coronary syndrome. Study registration: ClinicalTrials.gov, nos. NCT01994577; NCT02355457.

Prognostic implications of statin intolerance in stable coronary artery disease patients with different levels of high-sensitive troponin

Background

The prognostic implication of statin in tolerance (SI) in those with stable CAD remains unclear. We hypothesized that SI is of higher prognostic significance in stable CAD patients with elevated high-sensitive cardiac troponin I (hs-cTnI).

Methods

A total of 952 stable CAD patients from the prospective Hong Kong CAD study who had complete clinical data, biomarker measurements and who were prescribed statin therapy were studied.

Results

We identified 13 (1.4%) and 125 (13.1%) patients with complete and partial SI, respectively. At baseline, patients with SI were more likely to have diabetes mellitus and a higher hs-cTnI level, but no difference in LDL-C level compared with those without SI. After 51 months of follow-up, patients with SI had a higher mean LDL-C level than those without SI. A total of 148 (15.5%) patients developed major adverse cardiovascular events (MACEs). Both SI (HR 1.52, 95% CI 1.06–2.19, P = 0.02) and elevated hs-cTnI (HR 3.18, 95% CI 2.07–4.89, P < 0.01) were independent predictors of a MACE in patients with stable CAD. When stratified by hs-cTnI level, SI independently predicted MACE-free survival only in those with elevated hs-cTnI (HR 1.51, 95% CI 1.01–2.24, P = 0.04).

Conclusions

SI independently predicted MACE in patients with stable CAD and high hs-cTnI, but not in those with low hs-cTnI. Hs-cTnI may be used to stratify stable CAD patients who have SI for intensive lipid-lowering therapy using non-statin agents.

Electronic supplementary material

The online version of this article (10.1186/s12872-019-1152-x) contains supplementary material, which is available to authorized users.

Haemolysis and lipemia interfere with resistin and myeloperoxidase BioVendor ELISA assays

Introduction

The aim of our study was to investigate the influence of haemolysis and lipemia on resistin (RES) and myeloperoxidase (MPO) measurement by BioVendor enzyme-linked immunosorbent assays (ELISA).

Materials and methods

Blood was taken from healthy volunteers into lithium heparin tubes. Plasma samples were spiked with Lipofundin® emulsion (B. Braun Melsungen AG, Germany) for lipemia interference testing. Haemolysed samples were obtained by drawing aliquots of heparinized blood through a 26 gauge needle. Index of haemolysis (H), lipemia (L) and triglyceride concentration were measured on Abbott Architect c8000. Haemoglobin concentration was measured on Sysmex XN-1000. Concentrations of RES and MPO in all samples were determined with RES and MPO ELISA kits (BioVendor, Czech Republic). All measurements were performed in triplicate. Biases from the native samples were calculated for both analytes and compared with an arbitrary value (e.g. ± 10%).

Results

Triglyceride concentration in the investigated samples ranged from 0.57 to 38.23 mmol/L, which corresponds to L index from - 0.01 to 13.77. Haemoglobin concentration in all samples ranged from 0 to 8 g/L which correspond to H index from 0.05 to 8.77. Both MPO and RES showed significant biases at 1 g/L haemoglobin (58.7% and 66.7%, respectively). Also, both MPO and RES showed significant biases at 4.66 mmol/L triglycerides (33.8% and - 12.2%, respectively).

Conclusions

Resistin BioVendor assays are affected by haemolysis and lipemia already at low degree of interferent. Haemolysis was found to interfere at 1 g/L haemoglobin for both assays, while lipemia interferes at 4.66 mmol/L of triglycerides.

A false positive case of high-sensitivity cardiac troponin in a patient with acute chest pain: Analytical study of the interference

We report a case of a heterophile antibodies interference in a new high-sensitivity troponin commercial immunoassay (cTNIH Siemens), observed in a patient with possible acute coronary syndrome (ACS). The analytical interference was investigated with standard laboratories procedures. The false positive result was found with different troponin methods and kits. We also investigated the protein sequence of cTnl and no sequence variants were detected. The discordance between clinical pictures and high concentration of cTnl, together with the collaboration between clinicians and laboratory staff avoided possible erroneous diagnosis and further invasive investigations to the patient.

Revisiting the Biological Variability of Cardiac Troponin: Implications for Clinical Practice

The diagnosis of acute myocardial injury requires a rise and/or fall of cardiac troponin (cTn) on serial testing, with at least one concentration above the 99^th percentile value of a normal reference population according to the recently published Fourth Universal Definition of Myocardial Infarction.1 However, the magnitude of change in cTn that constitutes a significant rise and/or fall was again not specified in detail. High-sensitivity cardiac troponin (hs-cTn) assays can measure ten-fold lower concentrations of cTn with more precision than older assays, and can accurately quantify cTn in more than 50% of healthy individuals with a coefficient of variation of less than 10% at the 99^th percentile. These hs-cTn assays are also able to detect the normal variations in cTn results that are due to biological variability. Understanding and quantifying the normal variations in cTn is important as this would allow significant changes to be better defined. Numerous studies have sought to investigate the biological variability of cTn over the last ten years. Such studies are usually conducted in healthy individuals, however individuals with chronic cardiac disease or chronic renal failure have also been examined. These studies have yielded varying results in regards to significant change values for cTn. In light of the recent redefinition for myocardial infarction, the purpose of this mini-review is to revisit the biological variability of cTn. In particular, we outline concepts for determining a significant change value, review the results of previous studies on the biological variation of cTn and discuss potential considerations for clinical practice.