Analytical performance of a sensitive assay for cardiac troponin I with loci™ technology

Serial troponin-I and long-term outcomes in subjects with suspected acute coronary syndrome

AIMS

It is unclear how serial high-sensitivity troponin-I (hsTnI) concentrations affect long-term prognosis in individuals with suspected acute coronary syndrome (ACS).

METHODS AND RESULTS

Subjects who underwent two hsTnI measurements (Siemens TnI Flex® Reagent) separated by 1-7 h, during a first-time hospitalization for myocardial infarction, unstable angina, observation for suspected myocardial infarction, or chest pain from 2012 through 2019, were identified through Danish national registries. Individuals were stratified per their hsTnI concentration pattern (normal, rising, persistently elevated, or falling) and the magnitude of hsTnI concentration change (<20%, >20-50%, or >50% in either direction). We calculated absolute and relative mortality risks standardized to the distributions of risk factors for the entire study population. A total of 20 609 individuals were included of whom 2.3% had died at 30 days, and an additional 4.7% had died at 365 days. The standardized risk of death was highest among persons with a persistently elevated hsTnI concentration (0-30 days: 8.0%, 31-365 days: 11.1%) and lowest among those with two normal hsTnI concentrations (0-30 days: 0.5%, 31-365 days: 2.6%). In neither case did relative hsTnI concentration changes between measurements clearly affect mortality risk. Among persons with a rising hsTnI concentration pattern, 30-day mortality was higher in subjects with a >50% rise compared with those with a less pronounced rise (2.2% vs. <0.1%).

CONCLUSION

Among individuals with suspected ACS, those with a persistently elevated hsTnI concentration consistently had the highest risk of death. In subjects with two normal hsTnI concentrations, mortality was very low and not affected by the magnitude of change between measurements.

Transfusion in Older Anemic Patients: Should the Troponin Value Be Taken into Account?

BACKGROUND

Anemia is common in older individuals, but it is not known whether the prognostic impact of transfusion differs according to cardiac troponin concentration.

METHODS

During this 2-year retrospective study in an acute geriatric unit, 514 patients with hemoglobin <10 g/dL and troponin sampling were included. Thirty-day and 1-year mortality were compared according to transfusion status and troponin and hemoglobin levels.

RESULTS

Of the 514 anemic patients included (median age 88 years), 157 (31%) had elevated troponin concentrations. These patients were more likely to die at 30 days (49% vs 27%, P < .001) and 1 year (65% vs 51%, P = .004) than patients with normal values. Among patients with elevated troponin concentrations, 30-day mortality tended to be lower in transfused than in not-transfused patients (hazard ratio 0.48; 95% confidence interval, 0.21-1.08; P = .07). This association was not found in patients without troponin elevation (hazard ratio 1.09; 95% CI, 0.61-1.93; P = .8). Transfusion was associated with 30-day survival in patients with hemoglobin ≤8 g/dL. It was also associated with excess 1-year mortality in patients with hemoglobin >8 g/dL.

CONCLUSIONS

This pilot study suggests that transfusion could be associated with better 30-day outcomes in older anemic patients with anemia-related myocardial injury. Thus, troponin levels could be involved in decision-making relative to transfusion in anemic older patients. Clinical trials are needed to establish the benefit of transfusion in patients with elevated troponins.

A Case of Elevated Troponin I Level After Packed Red Blood Cell Transfusion With Normal Coronary Angiography

Other than acute coronary syndrome (ACS), many clinical conditions are associated with increased cardiac troponin I (cTnI) levels. Conditions such as pulmonary embolism, acute heart failure, myocarditis, sepsis, and renal failure are commonly reported as underlying causes. Analytical interference with the cTnI assay can also lead to falsely elevated troponin I levels. That can happen due to multiple causes such as fibrin clots, heterophile antibodies, microparticles contained in the sample, rheumatoid factor, interference by bilirubin, hemolysis, and elevated alkaline phosphatase activity. Herein, we present the case of a 66-year-old female who presented with pleuritic chest pain and had a cTnI of 35.5 ng/mL post-transfusion of three units of packed red blood cells. The patient had a complete ischemic workup for ACS, including coronary angiography, which was negative for coronary artery disease.

Effect of racing on cardiac troponin I concentration and associations with cardiac rhythm disturbances in Standardbred racehorses

INTRODUCTION/OBJECTIVES

Accumulating evidence indicates intense exercise can be associated with myocardial damage. Investigating the impact of maximal effort on myocardium and exploring possible association of injury with rhythm disturbance requires a high-sensitivity cardiac troponin assay. The objectives of this study were: (1) to determine the effect of racing on serum cardiac troponin I (cTnI) in Standardbred horses using a high-sensitivity assay; (2) to determine the 99th percentile of cTnI in healthy horses and investigate the effect of demographic variables on cTnI prevailing pre-race in Standardbred horses using a validated high-sensitivity assay and a contemporary assay, and; (3) to explore associations between exercise-associated arrhythmia and cTnI concentration.

ANIMALS

Racehorses (n = 145).

MATERIALS AND METHODS

≤ 2 h pre-race, cTnI concentrations were measured in 158 race starts. Electrocardiogram (ECG) monitoring was applied during racing and race recovery and screened for complex ventricular arrhythmia. Associations between cTnI prevailing before racing concentration, age, sex, and gait were investigated. Demographic and performance variables were evaluated for associations with cTnI concentration post-race and rhythm disturbance.

RESULTS

Incidence of arrhythmia was 11.6% (16 horses). A significant increase in median (interquartile range) cTnI concentration of 1.36 (0.49-2.81) ng/L was found post-race (p < 0.0001). Serum cardiac troponin I (cTnI) concentration prevailing pre-race was positively associated with increasing age, and gait. Serum cardiac troponin I prevailing post-race was positively associated with concentration prevailing pre-race. Interaction between arrhythmia and finishing distanced revealed horses finishing distanced and experiencing arrhythmia displayed higher cTnI release than with the presence of either alone.

CONCLUSIONS

Racing increased cTnI concentration. Horses finishing distanced and also exhibiting arrhythmia may be experiencing myocardial compromise.

Troponin Elevation in Older Patients with Acute Pneumonia: Frequency and Prognostic Value

Cardiovascular (CV) events are particularly frequent after acute pneumonia (AP) in the elderly. We aimed to assess whether cardiac troponin I, a specific biomarker of myocardial injury, independently predicts CV events and death after AP in older inpatients. Among 214 consecutive patients with AP aged ≥75 years admitted to a university hospital, 171 with a cardiac troponin I sample in the 72 h following diagnosis of AP were included, and 71 (42%) were found to have myocardial injury (troponin > 100 ng/L). Patients with and without myocardial injury were similar in terms of age, gender and comorbidities, but those with myocardial injury had more severe clinical presentation (median (interquartile range) Pneumonia Severity Index: 60 (40-95) vs. 45 (30-70), p = 0.003). Myocardial injury was strongly associated with in-hospital myocardial infarction (25% vs. 0%, p < 0.001), CV mortality (11 vs. 1%, p = 0.003) and all-cause mortality (34 vs. 13%, p = 0.002). After adjustment for confounders, myocardial injury remained a strong predictive factor of in-hospital mortality (odds ratio (95% confidence interval): 3.32 (1.42-7.73), p = 0.005) but not one-year mortality (1.61 (0.77-3.35), p = 0.2). Cardiac troponin I elevation, a specific biomarker of myocardial injury, was found in nearly half of an unselected cohort of older inpatients with AP and was associated with a threefold risk of in-hospital death.

Type 2 Myocardial Infarction: A Geriatric Population-based Model of Pathogenesis

Distinction between type 2 myocardial infarction (T2MI), defined as an imbalance between oxygen supply and demand without atherothrombosis, and type 1 myocardial infarction (T1MI), due to plaque disruption, is often a clinical challenge in frail elderly patients. We aimed to identify the characteristics and underlying causes of T2MI using a comprehensive geriatric approach. From a multicentre population-based prospective study in coronary care units, we adjudicated 4572 consecutive patients hospitalized for an acute T1MI or T2MI, according to the 3^rd universal definition and a prespecified geriatric model of T2MI pathogenesis. In total, 3710 (81%) had T1MI and 862 (19%) T2MI. Patients with T2MI were 10 y older (77 vs 67 y, p<0.001), more frequently female (44 vs 26%, p<0.001) and had more frequent comorbidities. In multivariate analysis, acute heart failure, tachycardia and C-reactive protein elevation at admission were associated with a higher risk of T2MI vs T1MI, whereas chest pain, troponin I peak > 10 µg/L and ST-segment elevation were associated with a lower risk. Underlying mechanisms leading to T2MI highlighted 3 main patterns: 1) Age-related physiological cardiovascular decline 2) chronic predisposing factors including chronic anaemia (10%) and severe aortic stenosis (7%), 3) acute triggering factors, the most common being acute infection (39%), mainly respiratory tract infection, followed by tachyarrhythmia (13%) and acute heart failure (10%). 122 (14%) patients had combined predisposing and triggering conditions for T2MI. In our large population-based survey of T2MI, chronic anaemia and severe aortic stenosis increased predisposition to T2MI and acute respiratory infection was by far the most frequent trigger. Our data shed new light on the age-related pathophysiological basis for discrepancies in oxygen supply and demand leading to MI.

Post-Infectious Myocardial Infarction: New Insights for Improved Screening

Acute infection is suspected of involvement in the onset of acute myocardial infarction (MI). We aimed to assess the incidence, pathogenesis and prognosis of post-infectious MI. All consecutive patients hospitalized for an acute MI in coronary care units were prospectively included. Post-infectious MI was defined by a concurrent diagnosis of acute infection at admission. Type 1 MI (acute plaque disruption) or Type 2 MI (imbalance in oxygen supply/demand) were adjudicated according to the universal definition of MI. From the 4573 patients admitted for acute MI, 466 (10%) had a concurrent acute infection (median age 78 (66-85) y, 60% male), of whom 313 (67%) had a respiratory tract infection. Type 2 MI was identified in 72% of post-infectious MI. Compared with other MI, post-infectious MI had a worse in-hospital outcome (11 vs. 6% mortality, p < 0.01), mostly from cardiovascular causes. After adjusting for confounders, acute infections were no more associated with mortality (odds ratio 0.72; 95% confidence interval 0.43-1.20). In the group of post-infectious MI, Type 1 MI and respiratory tract infection were associated with a worse prognosis (respective odds ratio 2.44; 95% confidence interval: 1.12-5.29, and 2.89; 1.19-6.99). In this large MI survey, post-infectious MI was common, accounting for 10% of all MI, and doubled in-hospital mortality. Respiratory tract infection and Type 1 post-infectious MI were associated with a worse prognosis.

Analytical evaluation of the new Beckman Coulter Access high sensitivity cardiac troponin I immunoassay

BACKGROUND

This study was aimed to evaluate the analytical performance of the novel chemiluminescent and fully-automated Beckman Coulter Access hsTnI high-sensitivity immunoassay for measurement of cardiac troponin I (cTnI).

METHODS

The study, using lithium heparin samples, included assessment of limit of blank (LOB), limit of detection (LOD), functional sensitivity, linearity, imprecision (within run, between-run and total), calculation of 99th percentile upper reference limit (URL) in 175 healthy blood donors (mean age, 36±12 years; 47% women) and comparison with two other commercial cTnI immunoassays.

RESULTS

The LOB, LOD and functional sensitivity of Access hsTnI were 0.14, 0.34 and 1.35 ng/L, respectively. The within-run, between-run and total imprecision was 2.2%-2.9%, 4.6%-5.4%, and 5.4%-6.1%, respectively. The linearity was excellent in the range of cTnI values between 0.95 and 4195 ng/L (r=1.00). The 99th percentile URL was 15.8 ng/L. Measurable cTnI values were found in 173/175 healthy subjects (98.9%). Good agreement of cTnI values was found with AccuTnI+3 (r=0.97; mean bias, -9.3%), whereas less satisfactory agreement was found with Siemens Dimension Vista cTnI (r=0.95; mean bias, -55%).

CONCLUSIONS

The results of our evaluation of the Beckman Coulter Access hsTnI indicate that the analytical performance of this fully-automated immunoassay is excellent.

Clinical performance of cardiac Troponin I: A comparison between the POCT AQT90 FLEX and the Dimension Vista analyzer in an emergency setting

BACKGROUND

Cardiac troponin [cTn (I or T)] is the preferred biomarker for the diagnosis of myocardial infarction (MI).

AIM

We studied the analytical performance of the POCT AQT90 FLEX cTnI assay and its diagnostic accuracy, in comparison to the Dimension Vista cTnI method, in patients presenting to the Emergency Department (ED) with suspect of acute coronary syndrome (ACS).

METHODS

786 consecutive patients were enrolled. cTnI was measured at admission to the ED and about 3 and 6 hours later. The imprecision study was carried out using different lots of quality controls (QCs). ROC curve analysis was conducted using discharge diagnoses in order to verify the global diagnostic accuracy.

RESULTS

The concentrations measured in the QCs ranging from 0.033 to 1.26μg/L show CVs% ranging from 2.81 to 7.56%, comparable to those declared by the manufacturer. Passing-Bablok and linear regression analysis show a high significant correlation (R²=0.90, p<0.0001); Bland-Altman test describes a statistically significant negative bias (Bias=-0.2336; 95%CI=-0.4217/-0.0456, p=0.0150). ROC curves obtained using Dimension Vista and AQT90 FLEX cTnI assays displayed similar clinical performance being not statistically significant the difference of the corresponding AUC. Comparing sensitivity and specificity of cTnI concentrations obtained from the ROC curve analysis using AQT90 FLEX, we found a "best cut-off" (0.014μg/L) lower than that declared from the manufacturer (0.023μg/L).

CONCLUSIONS

The comparison of two different assays of cTnI against a diagnosis of acute MI (AMI) shows that both assays behave equally well with a high degree of sensitivity and specificity. The resulting "best cut-off" suggests that this AQT90 FLEX cTnI concentration could be evaluated as the potentially new "clinically usable" cut-off for AMI/myocardial necrosis diagnoses.

Impact of physical activity of individuals and creatine kinase on 99th percentiles of troponin I assays

Determination of cardiac troponin I (cTnI) is one central means for diagnosis of myocardial infarction. Assay performance of three troponin I assays was compared previously in a large reference population detecting sex-differences in the 99th percentile only for the Dimension Vista cTnI assay. The present study examined the underlying effects. Values for cTnI were reused. Creatine kinase (CK) activity was determined in 2358 samples from blood donors. Information on physical activity was evaluated from health questionnaires. Using quantile regression data were analysed to investigate the impact of sex, physical activity, and CK on the 99th percentile of the cTnI assay. We report significant sex-differences for the 99th percentile of cTnI. Physical activity was significantly associated with cTnI values. Strong association of CK activity with cTnI values was detected only in men. Adjustment for CK in quantile regression abolished sex-differences in the 99th percentile. Two other contemporary sensitive cTnI assays were not relevantly affected by physical activity or CK. Sex-differences in the 99th percentile for the Dimension Vista cTnI assay arise from a positive association between cTnI and physical activity and were abrogated when data were adjusted for CK activity. These findings should be taken into account when using this assay.

High-density lipoprotein cholesterol values independently and inversely predict cardiac troponin T and I concentration

BACKGROUND

This retrospective study was planned to establish potential associations between circulating values of cardiac troponins and those of conventional blood lipids.

METHODS

The study population consisted of patients attending an inpatient clinic of the University Hospital of Verona during the year 2015 as part of routine cardiovascular risk assessment. No exclusion criteria were applied. Serum lipids including total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglycerides (TG) were measured using reference enzymatic techniques, whereas troponin T (TnT) was measured using a high-sensitivity (HS) immunoassay. A second analysis was also performed in the General Hospital of Verona, extracting data from the local laboratory database of all patients in whom troponin I (TnI) and blood lipids were simultaneously measured during the same year.

RESULTS

In univariate analysis, HS-TnT was found to be associated with age, sex, TC, LDL-C, HDL-C, but not with TG. In multivariate linear regression analysis, age (positive correlation; P<0.001) and HDL-C (negative correlation; P=0.032) remained significantly associated with HS-TnT. The frequency of HS-TnT values >50 ng/L was higher in subjects with HDL-C <1 mmol/L than in those with HDL-C ≥1 mmol/L [odds ratio (OR), 1.84; 95% confidence interval (CI), 1.03-3.32]. The frequency of HS-TnT values >50 ng/L was also higher in elderly subjects than in younger ones (OR, 2.10; 95% CI, 1.15-3.84). The combination of age and HDL-C explained 35% of overall variability of TnT concentration. In the second analysis, HDL-C was also found to be an independent and negative predictor of TnI in multivariate linear regression analysis (P=0.010). The combination of age and HDL-C explained approximately 28% of the overall variability of TnI concentration.

CONCLUSIONS

Our study suggests that HDL-C values inversely predict cardiac troponins concentration irrespective of age, sex and other blood lipids.

Systems for multiplexing homogeneous immunoassays

High-throughput multiplex protein biomarker assays continue to gain significance in the fields of biomarker discovery and drug development, due to their economical use of not only the precious clinical biological samples but also expensive reagents. Among these platforms, homogeneous multiplex systems have potential for short assay run times and cost-effective reagent consumptions. However, these systems must overcome challenges of signal cross talk and biochemical cross-reactivity. Despite these obstacles, several homogeneous multiplex immunoassays have been demonstrated. These include fluorescent polarization, fluorescent resonance energy transfer with quantum dots or graphene, luminescent oxygen-channeling immunoassay coupled with aqueous two-phase systems and DNA proximity assays. The balance between speed/simplicity and high multiplexing and robustness of these homogeneous multiplex immunoassays are discussed in this review.

Performance characteristics of loci method for measuring cardiac troponin I on the dimension EXL

Objective

To define the performance characteristics of the LOCI^® method for cardiac troponin I on the Dimension EXL system.

Designs and methods

Three different levels of commercial control (mean concentrations 0.426, 1.42, and 18.64 µg/L) were used for the imprecision study, quantifying separately within-run and between-run over 20 days. The limit of blank (LoB) and limit of detection (LoD) were assessed with 20 replicates of a sample without troponin I. Linearity was assessed by regression analysis. In addition, we studied inaccuracy, carry-over and limit of quantitation and conducted a method comparison with the Stratus CS (n=69). The reference interval was determined in 146 healthy blood donors using non-parametric method.

Results

The within-run imprecision (coefficient of variation [CV], %) obtained at each level was 2.4, 1.4% and 2.2%, while the between-run imprecision (CV,%) was 3.3%, 2.9% and 2.5%. Total imprecision was 4.06%, 3.3% and 3.4% for each control level. The limit of quantitation which corresponds to the troponin I concentration at which CV=10% was 0.05 µg/L. Method comparison with the Stratus CS assay produced the equation: Dimension EXL=−0.002698+1.0233^⁎(Stratus CS) with a confidence interval from −0.01562 to 0.00626 for the intercept and (0.979 to 1.0875) for the slope. The 99th percentile obtained for the reference population was 0.047 µg/L.

Conclusions

The LOCI method for cardiac troponin I on the Dimension EXL meets all guidelines recommended criteria referring to limit of quantitation, imprecision and shows excellent transferability with the Stratus CS method.

•

We found an acceptable imprecision. The linearity and limit of detection meet the manufacturer׳s specifications.

•

The 99th percentile in the reference population was 0.047 µg/L. The 10% CV cut-off was 0.050 µg/L.

•

The correlation with Stratus CS method was excellent.

The global need to define normality: the 99th percentile value of cardiac troponin

BACKGROUND

How to select a presumably normal population for the establishment of 99th percentile cutoffs for cardiac troponin assays has not been adequately addressed. Lack of attention to this question can result in misleading medical decision cutoffs.

CONTENT

From our review of the peer-reviewed literature, including international recommendations, no uniform procedure is followed and no uniform guideline has been published by experts or regulatory agencies to guide researchers or manufacturers of cardiac troponin assays in their quest to define the health or "normality" of a reference population that is used to establish an accurate 99th percentile value. As we progress globally into the era of high-sensitivity cardiac troponin assays, we propose several suggested approaches to define presumably normal individuals by use of clinical and biomarker surrogates.

SUMMARY

Our uniform approach to defining who is normal and who may not be normal will help to define diagnostic and risk outcomes assessments in the management of patients with suspected myocardial injury, both for use in current clinical practice and clinical research, as well as for the potential future use of cardiac troponin in primary prevention.

Comparison of the 99th percentiles of three troponin I assays in a large reference population

Background: The IFCC Task Force on Clinical Applications of Cardiac Biomarkers suggests comparing several contemporary sensitive troponin assays in the same, sufficiently large reference population.

Methods: Three contemporary sensitive assays were used to measure troponin I concentration in samples from a uniquely large healthy population (2404 individuals) and in a sub-group with tighter inclusion criteria of 908 individuals. The 99th percentiles were calculated using quantile regression which takes the entire population into account.

Results: The 99th percentile for the ARCHITECT STAT Troponin I assay was 21 ng/L, 31 ng/L for the ADVIA Centaur Troponin I-Ultra assay and 28 ng/L for the Dimension Vista cTnI assay. Significantly higher values were found in males than in women only in the Dimension Vista cTnI assay and in the subgroup for the ARCHITECT STAT Troponin I assay.

Conclusions: Quantile regression provides a tool to accurately estimate the 99th percentile and establish a continuous function of the relation between the 99th percentile and the age and gender. There was no age dependency demonstrated. A gender difference was found in one assay but inconclusive in another and not demonstrated in a third.

External evaluation of the Dimension Vista 1500® intelligent lab system

BACKGROUND

Dimension Vista® analyzer combines four technologies (photometry, nephelometry, V-LYTE® integrated multisensor potentiometry, and LOCI® chemiluminescence) into one high-throughput system.

METHODS

We assessed analytical performance of assays routinely performed in our emergency laboratory according to the VALTEC protocol, and practicability.

RESULTS

Precision was good for most parameters. Analytical domain was large and suitable for undiluted analysis in most clinical settings encountered in our hospital. Data were comparable and correlated to our routine analyzers (Roche Modular DP®, Abbott AXSYM®, Siemens Dimension® RxL, and BN ProSpec®). Performance of nephelometric and LOCI modules was excellent. Functional sensitivity of high-sensitivity C-reactive protein and cardiac troponin I were 0.165 mg/l and 0.03 ng/ml, respectively (coefficient of variation; CV < 10%). The influence of interfering substances (i.e., hemoglobin, bilirubin, or lipids) was moderate, and Dimension Vista® specifically alerted for interference according to HIL (hemolysis, icterus, lipemia) indices. Good instrument performance and full functionality (no reagent or sample carryover in the conditions evaluated, effective sample-volume detection, and clot detection) were confirmed. Simulated routine testing demonstrated excellent practicability, throughput, ease of use of software and security.

CONCLUSION

Performance and practicability of Dimension Vista® are highly suitable for both routine and emergency use. Since no volume detection and thus no warning is available on limited sample racks, pediatric samples require special caution to the Siemens protocol to be analyzed in secured conditions. Our experience in routine practice is also discussed, i.e., the impact of daily workload, "manual" steps resulting from dilutions and pediatric samples, maintenances, flex hydration on instrument's performance on throughput and turnaround time.

The importance of having a flexible scope ISO 15189 accreditation and quality specifications based on biological variation--the case of validation of the biochemistry analyzer Dimension Vista

INTRODUCTION

Technological innovation requires the laboratories to ensure that modifications or incorporations of new techniques do not alter the quality of their results. In an ISO 15189 accredited laboratory, flexible scope accreditation facilitates the inclusion of these changes prior to accreditation body evaluation. A strategy to perform the validation of a biochemistry analyzer in an accredited laboratory having a flexible scope is shown.

MATERIALS AND METHODS

A validation procedure including the evaluation of imprecision and bias of two Dimension Vista analysers 1500 was conducted. Comparability of patient results between one of them and the lately replaced Dimension RxL Max was evaluated. All studies followed the respective Clinical and Laboratory Standards Institute (CLSI) protocols. 30 chemistry assays were studied. Coefficients of variation, percent bias and total error were calculated for all tests and biological variation was considered as acceptance criteria. Quality control material and patient samples were used as test materials. Interchangeability of the results was established by processing forty patients' samples in both devices.

RESULTS

27 of the 30 studied parameters met allowable performance criteria. Sodium, chloride and magnesium did not fulfil acceptance criteria. Evidence of interchangeability of patient results was obtained for all parameters except magnesium, NT-proBNP, cTroponin I and C-reactive protein.

CONCLUSIONS

A laboratory having a well structured and documented validation procedure can opt to get a flexible scope of accreditation. In addition, performing these activities prior to use on patient samples may evidence technical issues which must be corrected to minimize their impact on patient results.

A comprehensive review of upper reference limits reported for (high-)sensitivity cardiac troponin assays: the challenges that lie ahead

Cardiac troponins (cTn) are the preferred markers for the diagnosis of acute myocardial infarction (AMI). The guidelines recommend the use of the 99th percentile upper reference concentration of a healthy population as the diagnostic cut-off for AMI. However, a broad range of upper reference limits is still employed, complicating the diagnosis of AMI. This overview is meant to assist laboratory specialists to define an appropriate cut-off value for the diagnosis of AMI. Therefore, we provide an overview of the analytical performance and upper reference limits of seven (high-)sensitivity cTn assays: Roche high-sensitivity cTnT and ADVIA Centaur, Stratus CS, Dimension Vista, Vitros ECi, Access and Architect cTnI assays. It is shown that none of the reference populations completely met the guidelines, including those in package inserts. Forty percent of the studies collected less than the advised minimum of 300 subjects. Many studies (50%) did not report their inclusion criteria, while lower 99th percentile limits were observed when more stringent selection criteria were applied. Higher troponin cut-offs were found in men and elderly subjects, suggesting sex- and age-specific cut-offs would be considered. Therefore, there is still need for a large, rigorously screened reference population to more accurately establish cTn upper reference limits.

Measurement of NT-proBNP with LOCI technology in heart failure patients

OBJECTIVES

The aim of our study was to determine NT-proBNP concentrations in heart failure (HF) patients with a luminescent oxygen channeling immunoassay (LOCI).

DESIGN AND METHODS

Seventy HF patients were enrolled. NT-proBNP levels were measured with LOCI method and compared to a reference NT-proBNP assay.

RESULTS

LOCI NT-proBNP levels were significantly correlated with the reference NT-proBNP assay and were related to HF severity.

CONCLUSIONS

LOCI assay demonstrates performances close to the comparative assay for NT-proBNP testing and allows a significant reduction of the time of analysis.