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

Reference values of galectin-3 and cardiac troponins derived from a single cohort of healthy blood donors

BACKGROUND

Here we describe the determination of upper reference limits (URL) for galectin-3, high-sensitivity cardiac troponin I (hs-cTnI) and high-sensitivity cardiac troponin T (hs-cTnT) in a single cohort of healthy blood donors using routine assays.

METHODS

For this reference value study, we used a cohort of 402 consecutive blood donors (64% were male and 36% were female). The median individuals' age was 35.0 years (range, 18.0-64.4). Individuals of this reference population were free of cardiovascular disease, diabetes mellitus, renal disease, cancer, current infection and chronic inflammatory disease. Plasma concentrations of galectin-3 were measured with the "routine Galectin-3" assay (Abbott Diagnostics), of hs-cTnI with the "STAT High Sensitive Troponin-I" assay (Abbott Diagnostics), and of hs-cTnT with the "Troponin T hs" assay (Roche Diagnostics). URLs were calculated by using a non-parametric percentile method.

RESULTS

The 97.5th percentile URL for galectin-3 was 16 ng/mL in males and 17 ng/mL in females; the 99 th percentile URL for hs-cTnI was 39 ng/L in males and 24 ng/L in females; and the 99 th percentile URL for hs-cTnT was 14 ng/L in males and 11 ng/L in females. Those individuals with hs-cTnI values ≥ 15 ng/L (n=8) were different from those individuals with hs-cTnT values ≥ 10 ng/L (n=7). Of the 402 individuals, none had galectin-3 values below the limit of detection (LOD, <1.0 ng/mL), 290 (72%) had hs-cTnI values below the LOD (i.e., 1.9 ng/L), and 359 (89%) had hs-cTnT values below the LOD (i.e., 5.0 ng/L).

CONCLUSION

Plasma concentrations of galectin-3, hs-cTnI and hs-cTnT and corresponding 99 th percentile URLs were rather low in our cohort of healthy blood donors compared with previously published data. In our reference population, analyte plasma concentrations above the LOD were detectable in 100% of the individuals with the Abbott galectin-3 assay, but only in less than 50% for both the Abbott hs-cTnI assay and the Roche hs-cTnT assay.

Reference Values and Release Kinetics of B-Type Natriuretic Peptide Signal Peptide in Patients with Acute Myocardial Infarction

BACKGROUND

The signal peptide for human B-type natriuretic peptide preprohormone (BNPsp), which is released from cardiomyocytes, is increased in plasma of patients with acute myocardial infarction (AMI); however, its exact release kinetics have not been defined.

METHODS

We measured BNPsp and high-sensitivity cardiac troponin T (hs-cTnT) in a reference group of individuals without structural heart disease (n = 285) and determined the release kinetics of these biomarkers in patients (n = 29) with hypertrophic obstructive cardiomyopathy undergoing transcoronary ablation of septal hypertrophy (TASH), a procedure allowing exact timing of onset of iatrogenic AMI. Blood samples were collected before TASH and at numerous preselected time points after TASH.

RESULTS

The reference median BNPsp concentration was 53.4 pmol/L [interquartile range (IQR) 47.0–61.0; 95th percentile 85.9 pmol/L; 99th percentile 116.3 pmol/L]. Baseline concentrations in patients undergoing TASH were higher than in the reference group [91.9 pmol/L (IQR 62.9–116.4); P &lt; 0.0001]. BNPsp increased significantly, peaking at 15 min after induction of AMI [149.6 pmol/L (109.5–204.9) vs baseline; P = 0.004] and declining slowly thereafter, falling below the preprocedural value after 8 h (P = 0.014). hs-cTnT increased significantly 15 min after induction of AMI [26 ng/L (19–39) vs 18 ng/L (11–29); P = 0.001] and remained high at all later time points.

CONCLUSIONS

BNPsp concentrations increased immediately after AMI induction, providing early evidence of myocardial injury. The release kinetics of BNPsp differed from those of hs-cTnT. These findings provide information that should help in establishing the diagnostic value of BNPsp in the setting of early AMI.

Portable nanoporous electrical biosensor for ultrasensitive detection of Troponin-T

AIM

To demonstrate the design, fabrication and testing of a portable, label-free biosensor for ultrasensitive detection of the cardiac Troponin-T (cTnT) from patient blood.

MATERIALS & METHODS

The biosensor is comprised of a nanoporous membrane integrated on to a microelectrode sensor platform for nanoconfinement effects. Charge perturbations due to antigen binding are recorded as impedance changes using electrochemical impedance spectroscopy.

RESULTS

The measured impedance change is used to quantitatively determine the cTnT concentration from the tested sample. We were successful in detecting and quantifying cardiac Troponin-T from a 40-patient cohort. The limit of detection was 0.01 pg/ml.

CONCLUSION

This novel technology has promising preliminary results for rapid and sensitive detection of cTnT.

Impact on Patient Management and Outcome of Switching between 2 Contemporary Sensitive Cardiac Troponin Assays

BACKGROUND

Myocardial infarction is characterized by an increase of cardiac troponin I (cTnI) above the 99th percentile of a reference population. Our hospital switched from 1 contemporary cTnI assay to another and observed a doubling of cTnI results above the assays' respective 99th percentile cutoffs. We investigated the potential impact on inpatient management and outcomes.

METHODS

We performed a retrospective cohort study of 45 498 individuals with ≥1 cTnI result between January 2013 and June 2014. The Dimension cTnI assay was used in 2013; the Abbott Architect cTnI assay was used in 2014.

RESULTS

Before switching cTnI assays, 19.2% (4742/30 872) of patients had at least 1 of the first 3 cTnIs above the 99th percentile (0.07 μg/L). After switching to the Architect cTnI assay, 31.4% (4034/14 626) of patients had at least 1 cTnI above the 99th percentile (0.03 μg/L). This increase was due to the difference in the assays' 99th percentile cutoffs. Having an increased cTnI reported on the Architect assay that would not have been reported as such on the Dimension assay (0.03–0.06 μg/L) correlated with increased inpatient mortality, length of stay, non–ST elevation myocardial infarction diagnosis, therapeutic heparin use, and percutaneous coronary intervention, relative to individuals with cTnI &lt;0.03 μg/L.

CONCLUSIONS

The changes observed in patient outcomes and management were likely due to the increased sensitivity and lower 99th percentile cutoff of the Architect assay. It is important to recognize the potential impact that differences in sensitivity and assay configuration may have on patient management.

Optimal Cutoff Levels of More Sensitive Cardiac Troponin Assays for the Early Diagnosis of Myocardial Infarction in Patients With Renal Dysfunction

Supplemental Digital Content is available in the text.

Background—

It is unknown whether more sensitive cardiac troponin (cTn) assays maintain their clinical utility in patients with renal dysfunction. Moreover, their optimal cutoff levels in this vulnerable patient population have not previously been defined.

Methods and Results—

In this multicenter study, we examined the clinical utility of 7 more sensitive cTn assays (3 sensitive and 4 high-sensitivity cTn assays) in patients presenting with symptoms suggestive of acute myocardial infarction. Among 2813 unselected patients, 447 (16%) had renal dysfunction (defined as Modification of Diet in Renal Disease–estimated glomerular filtration rate <60 mL·min⁻¹·1.73 m⁻²). The final diagnosis was centrally adjudicated by 2 independent cardiologists using all available information, including coronary angiography and serial levels of high-sensitivity cTnT. Acute myocardial infarction was the final diagnosis in 36% of all patients with renal dysfunction. Among patients with renal dysfunction and elevated baseline cTn levels (≥99th percentile), acute myocardial infarction was the most common diagnosis for all assays (range, 45%–80%). In patients with renal dysfunction, diagnostic accuracy at presentation, quantified by the area under the receiver-operator characteristic curve, was 0.87 to 0.89 with no significant differences between the 7 more sensitive cTn assays and further increased to 0.91 to 0.95 at 3 hours. Overall, the area under the receiver-operator characteristic curve in patients with renal dysfunction was only slightly lower than in patients with normal renal function. The optimal receiver-operator characteristic curve–derived cTn cutoff levels in patients with renal dysfunction were significantly higher compared with those in patients with normal renal function (factor, 1.9–3.4).

Conclusions—

More sensitive cTn assays maintain high diagnostic accuracy in patients with renal dysfunction. To ensure the best possible clinical use, assay-specific optimal cutoff levels, which are higher in patients with renal dysfunction, should be considered.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00470587.

A national survey of troponin testing and recommendations for improved practice

Background

The introduction of troponin assays with higher analytical sensitivity and enhanced performance has produced new challenges for both laboratory and clinician in the optimal investigation of patients with cardiovascular disease. After some years of collective experience with this new generation of assays, this survey aimed to assess the level of consensus that exists regarding their application.

Methods

A questionnaire was designed, based on a review of published evidence and current opinion, to obtain information on a number of key areas relating to troponin analysis and reporting and was circulated to lead laboratory consultants across the UK and Ireland.

Results

Completed questionnaires were received from 94 laboratory contacts. Sixty per cent of those who responded had implemented a high-sensitivity troponin assay, with the Roche Cobas troponin T high sensitivity assay the most widely used. It is evident that some confusion remains regarding the definition of high-sensitivity assays and there was considerable variation in practice, even among those using the same manufacturer’s assay.

Conclusions

There is a need for greater consensus in the approach to the clinical utilization of troponin assays with improved sensitivity and it is important that laboratories are fully aware of the capabilities of their assay and provide useful guidance to users. On the basis of survey findings and the existing evidence base, a number of recommendations have been proposed to improve current practice and enhance patient safety.

Decision limits and the reporting of cardiac troponin: Meeting the needs of both the cardiologist and the ED physician

Cardiac troponin is the preferred biomarker for defining the acute coronary syndrome and acute myocardial infarction. Currently, the only decision limit formally endorsed with regard to the cardiac troponins is the 99th percentile. This is a "rule-in" criterion, intended to ensure that only persons with the acute coronary syndrome are reviewed. The 99th percentile is an arbitrary cut point and there are many problems associated with its application, including defining a truly healthy population, the difficulty of standardisation of cardiac troponin assays, especially but not only cardiac troponin I, and the effects of age and sex on this parameter. The Emergency Department (ED) screens many more persons for possible acute coronary syndromes than actually have the condition and their needs are best met by a "rule-out" test that enables them to clear their busy departments of the many persons who do not actually have the condition. The needs of the ED are not optimally met using the 99th percentile. The index of individuality for the cardiac troponins is small and significant changes consistent with an acute coronary syndrome can occur without the 99th percentile being exceeded. It appears that the ED may be better served by use of delta troponin changes rather than the 99th percentile, but there are problems with this approach, particularly in persons who present late when troponin release has plateaued. In addition, there are many non-acute coronary syndrome causes for cardiac troponin release. The needs of the cardiologist and the ED physician are so different that it may be inappropriate for both groups to use the same diagnostic criteria for cardiac troponin, and it is of great importance that cardiac troponin measurement be used as only one part of the assessment of the person presenting with possible acute coronary syndrome.

Diabetes mellitus, prediabetes, and incidence of subclinical myocardial damage

BACKGROUND

Persons with prediabetes and diabetes mellitus are at high risk for cardiovascular events. However, the relationships of prediabetes and diabetes mellitus to the development of subclinical myocardial damage are unclear.

METHODS AND RESULTS

We measured cardiac troponin T with a highly sensitive assay (hs-cTnT) at 2 time points, 6 years apart, among 9051 participants of the community-based Atherosclerosis Risk in Communities Study with no diabetes mellitus, or prediabetes, and without cardiovascular disease including silent myocardial infarction by ECG. First, we examined the incidence of elevated hs-cTnT (≥14 ng/L) at 6 years of follow-up. Second, we examined clinical outcomes during the subsequent ≈14 years of follow-up among persons with and without incident elevations in hs-cTnT. Cumulative probabilities of elevated hs-cTnT at 6 years among persons with no diabetes mellitus, prediabetes, and diabetes mellitus were 3.7%, 6.4%, and 10.8%, respectively. Compared with normoglycemic persons, the adjusted relative risks for incident elevated hs-cTnT were 1.40 (95% CI, 1.08-1.80) for prediabetes and 2.47 (95% CI, 1.78-3.43) for diabetes mellitus. Persons with diabetes mellitus and incident elevations in hs-cTnT were at a substantially higher risk of heart failure (hazard ratio, 6.37 [95% CI, 4.27-9.51]), death (hazard ratio, 4.36 [95% CI, 3.14-6.07]), and coronary heart disease (hazard ratio, 3.84 [95% CI, 2.52-5.84]) compared with persons without diabetes mellitus and no incident elevation in hs-cTnT.

CONCLUSIONS

Prediabetes and diabetes mellitus were independently associated with the development of subclinical myocardial damage, as assessed by hs-cTnT, and those persons with evidence of subclinical damage were at highest risk for clinical events. These results support a possible deleterious effect of hyperglycemia on the myocardium, possibly reflecting a microvascular cause.

The calculation of the cardiac troponin T 99th percentile of the reference population is affected by age, gender, and population selection: a multicenter study in Italy

BACKGROUND

The aim of this study is to determine the 99th upper-reference limit (URL) for cardiac troponin T (cTnT) in Italian apparently healthy subjects.

METHODS

The reference population was selected from 5 cities: Bolzano (n=290), Milano (CAMELIA-Study, n=287), Montignoso (MEHLP-Study, n=306), Pisa (n=182), and Reggio Calabria (MAREA-Study, n=535). Subjects having cardiac/systemic acute/chronic diseases were excluded. Participants to MEHLP project underwent cardiac imaging investigation. High-sensitive cTnT was measured with Cobas-e411 (Roche Diagnostics).

RESULTS

We enrolled 1600 healthy subjects [54.6% males; age range 10-90years; mean (SD): 36.4 (21.2) years], including 34.6% aged <20years, 54.5% between 20 and 64years, and 10.9% over 65years. In the youngest the 99th URL was 10.9ng/L in males and 6.8ng/L in females; in adults 23.2ng/L and 10.2ng/L; and in elderly 36.8ng/L and 28.6ng/L. After the exclusion of outliers the 99th URL values were significantly decreased (P<0.05) in particular those of the oldest (13.8ng/L and 14ng/L). MEHLP participants were divided in healthy and asymptomatic, according to known cardiovascular risk factors (HDL, LDL, glucose, C-reactive protein): the 99th URL of cTnT values of these subgroups was significantly different (19.5 vs. 22.7, P<0.05).

CONCLUSIONS

99th URL of cTnT values was strongly affected by age, gender, selection of subjects and the statistical evaluation of outliers.

Chimeric recombinant antibody fragments in cardiac troponin I immunoassay

OBJECTIVES

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

DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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