99th Percentile Limit Research Articles

Abstract 15828: Baseline Hs-ctnt Concentrations Within the Sex-Specific Reference Range and Index Mortality in Emergency Department Patients

Background: High-sensitivity (hs) cardiac troponin (cTn) assays quantifies cTn in most healthy men and women. Whether quantifiable cTn concentrations below the 99 th percentile upper-reference limit have short term prognostic implications in emergency department (ED) patients remains uncertain. Methods: Multicenter (n=22) United States (US) cohort of ED patients undergoing at least one hs-cTnT measurement (CV Data Mart Biomarker cohort). For this assay, the lowest reportable concentration is <6 ng/L. Sex-specific 99 th percentiles of 10 ng/L for women and 15 ng/L for men were used. The primary outcome was index hospitalization mortality. Results: A total of 85610 patients were examined, including 43043 women and 42567 men. A total of 775 index hospitalization deaths (0.91%) occurred, including 361 (0.84%) in women and 414 (0.97%) in men. Among women, baseline hs-cTnT concentrations were non-quantifiable (<LoQ) in 37.5%, quantifiable (LoQ-99 th ) in 21.6%, and increased >99 th percentile in 40.9%. Among men, baseline hs-cTnT concentrations were non-quantifiable (<LoQ) in 20.0%, quantifiable (LoQ-99 th ) in 37.4%, and increased >99 th percentile in 42.6%. Patients with higher concentrations were more likely to be older and had more comorbidities. Continuous baseline hs-cTnT (log) were associated with a higher odds of index hospitalization mortality (OR 1.26, 95% CI 1.24-1.28). Following multivariable analyses, quantifiable hs-cTnT (LoQ-99 th ) also were associated with index hospitalization mortality in all patients (OR 2.07, 95% 1.22-3.53), and in both women (OR 3.13, 95% CI 1.51-6.50) and men (OR 2.17, 95% 1.28-3.69) (Figure). Conclusions: Hs-cTnT concentrations within the reference range are more common in men than in women. Quantifiable hs-cTnT concentrations within the sex-specific reference range are associated with a higher risk of index hospitalization mortality, with a larger prognostic effect in women than in men.

Reference limits of high-sensitive cardiac troponin T indirectly estimated by a new approach applying data mining. A special example for measurands with a relatively high percentage of values at or below the detection limit

Abstract A new model for the indirect estimation of reference limits (RLs) has been proposed recently and was coined TMC approach (truncated minimum chi-square estimation) which can be performed with R statistic. A spline function is applied to the RLs to get a continuous function if age is graphically presented vs. the RLs avoiding artificial “jumps” between different age groups. Most indirect models assume a power normal distribution and fail if this assumption is not fulfilled as e.g. if a relatively high percentage of measured values is below the detection limit and the data are distributed extremely skewed. This problem is handled by the TMC model. High-sensitive cardiac troponin T (hs cTnT) was chosen as an example. The hs cTnT concentration in serum or plasma is well accepted as a valuable marker in the diagnosis of acute myocardial infarction. Currently, the 99th percentile derived from a “healthy” subpopulation is the decision limit recommended by consensus groups. However, this decision limit is questioned by several authors for many reasons. In the present report, the 97.5th and the 99th percentile limits were reinvestigated by the TMC model with different subpopulations stratified according to age and sex and were finally compared to presently recommended decision limits. In summary, the generally recommended 99th percentile as a fixed decision limit should be reconsidered. It is suggested to apply more specific reference limits stratified for age and sex instead of a fixed decision limit.

Abstract 17152: Artificial Intelligence ECG for the Detection of Cardiac Injury as Confirmed by High Sensitivity Cardiac Troponin T-Concentrations

Background: High-sensitivity cardiac troponin (hs-cTn) assays quantify cTn in patients at very low concentrations. Myocyte injury due to ischemia or other pathologies cause blood levels to increase, which is prognostic. A noninvasive, rapid, broadly available, home-based test to detect hs-cTn increases would facilitate risk-stratification. Since myocyte injury is associated with ECG changes, we hypothesized an artificial intelligence ECG (AI-ECG) could non-invasively predict current or impending hs-cTnT elevations. Objective: To develop an AI-ECG convolutional neural network (CNN) to detect an abnormal hs-cTnT (5 th Gen cTnT, Roche Diagnostics) concentration using a 12-lead ECG, and a single lead ECG (lead I), which would enable smartphone, home-based detection. Methods: We developed single lead and 12-lead ECG CNNs to detect a) hs-cTnT concentrations that were at or above the 6ng/L limit that can be reported b) above the 99 th percentile upper limits of >15ng/L for men and >10ng/L for women. All ECGs were recorded within one hour of the hs-cTnT measurements. We used 73,012 ECG and hs-cTnT pairs from 47,542 unique patients to train the network, 9031 ECGs from 5,811 patients for internal validation to optimize hyperparameters, and 18,276 ECG and hs-cTnT pairs from 11,904 different patients as a holdout test set to determine the area under the receiver-operator curve (AUC). Results: The mean age was 63.9±17.5 years, and 30,348 of the 59,446 patients (51%) were male. Of the 91,288 hs-cTnT pairs 73,271 (80.2%) were above 6ng/L and 50,799 (55.6%) are above the 99 th percentile. In the test set, the AUC for the detection of a hs-cTnT level higher than 6ng/L was 0.88 using the 12 lead ECG and 0.834 with the single lead. For the detection of hs-cTnT level above of 99 th percentile, the 12 lead ECG AUC was 0.853 and the single lead was 0.806. Conclusion: The AI-ECG permits detection of levels of hs-cTnT consistent with myocardial injury. This may allow a home-based, non-invasive test that would be massively scalable and could further enhance rapid-risk stratification and patient triage with potentially significant cost reductions and enable novel triage strategies at sites without hs-cTn assays.

No Massive Companion to the Coherent Radio-emitting M Dwarf GJ 1151

Abstract The recent detection of circularly polarized, long-duration (>8 hr), low-frequency (∼150 MHz) radio emission from the M4.5 dwarf GJ 1151 has been interpreted as arising from a star–planet interaction via the electron cyclotron maser instability. The existence or parameters of the proposed planets have not been determined. Using 20 new HARPS-N observations, we put 99th-percentile upper limits on the mass of any close companion to GJ 1151 at . With no stellar, brown dwarf, or giant planet companion likely in a close orbit, our data are consistent with detected radio emission emerging from a magnetic interaction between a short-period terrestrial-mass planet and GJ 1151 (https://github.com/benjaminpope/video).

Abnormal elevation of myocardial necrosis biomarkers after coronary artery bypass grafting without established myocardial infarction assessed by cardiac magnetic resonance

BackgroundThe diagnosis of peri-procedural myocardial infarction is complex, especially after the emergence of high-sensitivity markers of myocardial necrosis.MethodsIn this study, patients with normal baseline cardiac biomarkers and formal indication for elective on-pump coronary bypass surgery were evaluated. Electrocardiograms, cardiac biomarkers, and cardiac magnetic resonance imaging with late gadolinium enhancement were performed before and after procedures. Myocardial infarction was defined as more than ten times the upper reference limit of the 99th percentile for troponin I and for creatine kinase isoform (CK-MB) and by the findings of new late gadolinium enhancement on cardiac magnetic resonance. We assessed the release of cardiac biomarkers in patients with no evidence of myocardial infarction on cardiac magnetic resonance.ResultsOf 75 patients referred for on-pump coronary bypass surgery, 54 (100%) did not have evidence of myocardial infarction on cardiac magnetic resonance. However, all had a peak troponin I above the 99th percentile; 52 (96%) had an elevation 10 times higher than the 99th percentile. Regarding CK-MB, 54 (100%) patients had a peak CK-MB above the 99th percentile limit, and only 13 (24%) had an elevation greater than 10 times the 99th percentile. The median value of troponin I peak was 3.15 (1.2 to 3.9) ng/mL, which represented 78.7 times the 99th percentile.ConclusionIn this study, different from CK-MB findings, troponin was significantly increased in the absence of myocardial infarction on cardiac magnetic resonance. Thus, CK-MB was more accurate than troponin I for excluding procedure-related myocardial infarction. These data suggest a higher troponin cutoff for the diagnosis of coronary bypass surgery related myocardial infarction.Clinical trial registrationhttp://www.isrctn.com/ISRCTN09454308. Registered 08 May 2012.

Total and Differential Leukocyte Count Percentiles in Healthy Singleton Term Women during the First Stage of Labor

Aims: To establish leukocyte count and differential percentiles in healthy singleton term laboring women during spontaneous normal vaginal labor following an uncomplicated pregnancy. Methods: An analysis of the records of all women (n = 762) who delivered at our delivery ward during a 2-month period was performed. After exclusion for cesarean delivery, induction of labor, pregnancy complications, preterm labor, multiple pregnancy, fever on admission, and lack of full blood count on admission, 365 parturient women during the 1st stage of labor were included in the final analysis. The total and differential leukocyte counts were determined by standard procedure by an automated cell counter. Results: The leukocyte count range on admission to the delivery ward during the 1st stage of labor in healthy parturient women was between 4.4 × and 21.7 × 10³/µl and the 99th percentile limit was 20.06 × 10³/µl. The total leukocyte count was not influenced by cervical dilatation, ruptured membranes, or the presence and regularity of uterine contractions. Conclusion: An observed leukocyte count within the 99th percentile limit (20.06 × 10³/µl) in an otherwise normal parturient woman is reassuring in the absence of other clinical evidence.

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.

Characterisation of a highly sensitive troponin I assay and its application to a cardio-healthy population

Abbott Diagnostics have developed a new highly sensitive troponin I (hs-TnI) assay. We have assessed its analytical characteristics and applied the assay to a population of apparently cardio-healthy persons. We assessed imprecision, bias compared to the previous generation assay, matrix effects, and interferences and applied the assay to an apparently healthy population, deriving the 99th percentile limit of the distribution of values in reference populations for men and women separately. The dynamic range of the assay was ranged from 0.5-50,000 ng/L (pg/mL). The 10% CV was at a concentration of 3.9 ng/L, and the 20% CV was at a concentration of 1.8 ng/L. The new and current version of the TnI assay were highly correlated [slope: 0.98 (95%CI:0.88-1.07), y-intercept:1.20 (95%CI:-2.35-4.75) r²=0.99]. The 99th percentile limit of the distribution of values in a reference population was different for males and females: for males 14.0 ng/L and for females 11.1 ng/L and at these concentrations the assay CV was 5.0%. TnI was detectable in nearly all patient samples from the healthy reference population (98.6%). This new hs-TnI assay is able to measure to an order of magnitude lower than the current generation TnI assay from the same manufacturer. With TnI being detectable in nearly all apparently healthy subject samples this suggests that TnI presence does not always indicate cardiomyocyte necrosis.

Skeletal Muscle Biomarkers in Heart Disease

On the other hand, methods on the market are nonstandardized, causing significantly different 99th percentile limits across the cTn assays [6]. Heterogeneity between assays is caused by the use of different antibodies for capture and detection of circulating cTn forms. A practical and convenient approach to deal with these differences has been proposed by Apple [6]. One of the factors taken into account in his scorecard for individual cTn assays is the analytical criterion recommended by the international guidelines, which requires a total imprecision equal to or less than 10% at the 99th percentile value [1,2]. Assays that are compatible with this requirement are designated as ‘guideline acceptable’. Using 20% as the maximal acceptable imprecision excludes a contemporary assay from clinical use, and assays with an imprecision between 10 and 20% are indicated as ‘clinically usable’ [6]. Another analytical issue that is important for clinical interpretation of cTn results is the impact of interferences. For example, human antimouse antibodies and rheumatoid factor cause falsely increased cTn, while anti-cTn autoantibodies cause falsely decreased cTn [7,8]. The influence of hemolysis appears to be method dependent, as it has been reported to increase cTnI on Vitros ECi (Ortho-Clinical Diagnostics) and to decrease cTnT on Roche instruments [9].

Comparison of different methods of inter-eye asymmetry of rim area and disc area analysis

To describe different methods of inter-eye asymmetry of rim area (RA) to disc area (DA) asymmetry ratio (RADAAR) analysis. This was an observational, descriptive, and cross-sectional study. Both the eyes of all participants underwent confocal scanning laser ophthalmoscopy (Heidelberg retina tomograph (HRT 3)), frequency-doubling technology perimetry (FDT), and complete ophthalmological examination. Based on ophthalmological clinical examination and FDT results of the worse eye, subjects were classified as either normal, possible glaucoma, and probable glaucoma or definitive glaucoma. RADAAR values were calculated based on stereometric HRT 3 values using different mathematical formulae. RADAAR-1 was calculated as a relative difference of rim and DAs between the eyes. RADAAR-2 was calculated by subtracting the value of rim to DA ratio of the smaller disc from the value of rim to DA ratio of the larger disc. RADAAR-3 was calculated by dividing the previous two values. Statistical analyses included ANOVA as well as Student t-tests. Data of 334 participants were analysed, 78 of which were classified as definitive glaucoma. RADAAR-1 values were significantly different between the four different groups of diagnosis (F=5.82; P<0.001). The 1st and 99th percentile limits of normality for RADAAR-1, RADAAR-2, and RADAAR-3 in normal group were, respectively, -10.64 and 8.4; -0.32 and 0.22; and 0.58 and 1.32. RADAAR-1 seems to best distinguish between the diagnostic groups. Knowledge of RADAAR distribution in various diagnostic groups may aid in clinical diagnosis of asymmetric glaucomatous damage.

A practical assessment of the short-term in vitro stability of troponin I at the 99th percentile

Serial troponin measurement is important for the diagnosis of myocardial infarction. As troponin concentrations approach the cut-off for detectable myocardial necrosis, smaller changes in troponin as a result of decreased in vitro stability may be sufficient to generate changes of apparent clinical significance. This is particularly relevant regarding retrospective 'add-on' testing on samples several hours after venepuncture. We investigated the stability of troponin I (cTnI) at values close to the 99th percentile limit. Serum samples with baseline cTnI concentrations in the range 0.04-0.15 μg/L were analysed routinely using the Siemens TnI-Ultra assay. Follow-up analysis was carried out at 6, 9, 12, 24 and 48 h post-venepuncture after storage at room temperature and in the cold room. There was a significant decrease in cTnI concentration after 6 h post-venepuncture compared with baseline levels (P < 0.001). The maximum percentage change was -17.1% observed after 48 h storage at room temperature. Of samples with baseline cTnI concentration 0.040 μg/L, 80% had a cTnI concentration below 0.040 μg/L on re-analysis after 6 h. Requests for retrospective addition of troponin measurement on samples several hours after venepuncture is commonplace in many laboratories. Analysis of samples drawn >6 h previously may produce values below the cut-off for myocardial necrosis (0.040 μg/L) that would have been detectable if measured earlier as a result of decreased in vitro stability. Significant percentage decreases in cTnI concentration following storage may also have implications in lowering the threshold for an apparently clinically significant change to occur.

Yenidoğan Cinsiyeti ve Gebelik Yaşı Kord Kanı Troponin I Seviyesinin Bağımsız Belirleyicileridir

Objective: Troponin is an inhibitory protein complex located on the actin flament in all striated muscles. Cardiac Troponin I is found only in the heart and has been used as a sensitive and specific marker of myocardial injury. Our aim was to investigate the different percentile limits and determinants of cord blood cardiac Troponin I (Tn I) concentrations. Material and Methods: A total of 378 consecutive healthy neonates were included in the study. Umbilical cord arterial and venous blood samples were obtained at the time of delivery. Concentrations and determinants of cardiac Tn I were analyzed using multivariate analysis, and percentile values were calculated. Results: Multivariate analyses showed that gestational age in weeks (B= -0.17, p= 0.02, t= -2.3) and fetal gender (B= -0.11, p=0.03, t= -2.08) were independent determinants of cord blood cardiac Tn I concentrations. The cases were divided into term (? 37 weeks of gestation) and pretem (<37 weeks of gestation) subgroups for the ease of clinical evaluation. The demographic variables of mothers of term and preterm infants were similar (p> 0.05) except for gestational age (p< 0.01). Mothers of preterm cases had significantly more frequent tocolytic therapy, early rupture of membranes, hypertension and cesarean delivery (p< 0.01). Term infants had more frequent labor induction and labor augmentation (p< 0.01). The 99th percentile limits of cardiac Tn I were 3.8 ng/ml in male (n= 47) and 0.8 ng/ml in female (n= 32) for pre-terms. In term neonates, these values were 2.7 ng/ml in males (n= 166) and 3.1 ng/ml in females (n= 133). Conclusion: This study reports the different cardiac Tn I percentile limits in a neonatal population. Our results suggested that the upper reference limits for cardiac Tn I may vary according to gestational age and gender.

High-Sensitive Troponin Testing and the “Runner's Syndrome”

Despite improved clinical care, heightened public awareness, and widespread health innovations, myocardial infarction (MI) is still responsible for nearly 12 million deaths worldwide each year, causing half of all deaths in several developed countries and representing one of the main causes of death in many developing countries. Nearly 2400 Americans die of MI each day, an average of 1 death every 37 s. It is estimated that in 2009, 785,000 Americans will have a new coronary attack, and about 470,000 will have a recurrent attack ( 1 American Heart AssociationHeart disease and stroke statistics—2009 update. http://www.americanheart.org/presenter.jhtml?identifier=3037327 Google Scholar ). Therefore, further efforts should be placed on early, accurate diagnosis and appropriate triage to prevent mortality and related morbidity ( 1 American Heart AssociationHeart disease and stroke statistics—2009 update. http://www.americanheart.org/presenter.jhtml?identifier=3037327 Google Scholar ). According to the new universal definition of MI, troponin testing is of paramount importance (if not the mainstay) in the diagnosis, because MI is diagnosed in the presence of clinical evidence of ischemia when blood levels of this most sensitive and specific biomarker are increased above the 99th percentile of a normal reference population ( 2 Thygesen K. Alpert J.S. White H.D. Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial InfarctionUniversal definition of myocardial infarction. Circulation. 2007; 116: 2634-2653 Crossref PubMed Scopus (2122) Google Scholar ). With the advent of the high-sensitive (hs) cardiac troponin T (cTnT) and I (cTnI) assays, however, a paradigm shift has occurred in the detection of myocardial stress, injury, ischemia, and infarction, as well as in the clinical management of patients with slightly increased troponin concentrations in blood. At variance with the traditional cardiac troponin cTnT assay (Roche Diagnostics; Basel, Switzerland), whose traditional cutoff is 0.03 μg/L, the 10%-Coefficient of Variation (CV) cutoff concentration of the new hs-cTnT immunoassay from Roche Diagnostics is as low as 0.009 μg/L, which is even lower than the 99th percentile value of the reference population (0.016 μg/L, diagnostic cutoff) ( 3 Mingels A. Jacobs L. Michielsen E. Swaanenburg J. Wodzig W. van Dieijen-Visser M. Reference population and marathon runner sera assessed by highly sensitive cardiac troponin T and commercial cardiac troponin T and I assays. Clin Chem. 2009; 55: 101-108 Crossref Scopus (246) Google Scholar ). Likewise, cTnT, the 10%-CV concentration of a new hs-cardiac Troponin I (cTnI) assay (Hs-cTnI assay, Beckman Coulter; Fullerton, CA, USA), has been reported to be as low as 8.66 ng/L, with 99th percentile estimates in lithium, heparin, serum, and ethylenediaminetetraacetic acid plasma of 9.20, 8.00, and 8.60 ng/L, respectively (the 99th percentile limit of the traditional Beckman Coulter AccuTnI assay is 0.04 μg/L) ( 4 Kavsak P.A. MacRae A.R. Yerna M.J. Jaffe A.S. Analytic and clinical utility of a next-generation, highly sensitive cardiac troponin I assay for early detection of myocardial injury. Clin Chem. 2009; 55: 573-577 Crossref PubMed Scopus (141) Google Scholar ).

The impact of micro troponin leak on long‐term outcomes following elective percutaneous coronary intervention

To evaluate the clinical impact of microleaks of troponin, which are below the reference standard defining troponin elevation, on cardiovascular outcomes in stable coronary patients undergoing elective percutaneous coronary intervention (PCI). Troponin elevation, either pre- or post-PCI, has been shown to predict poor cardiovascular outcomes. However, troponin measurements that are above the limit of detection but below the 99th percentile limit defining elevation ("microleak") have uncertain clinical significance. We assessed subsequent myocardial infarction (MI) and death over a mean follow-up of 4.2 years in 2,272 patients undergoing elective PCI, where baseline troponins were normal and follow-up troponins were obtained 12-24 hr post-PCI. Patients were divided into three groups based on post-PCI troponin levels: Group 1 (n = 1,313) nondetectable; group 2 (n = 587) microleak, and group 3 (n = 372) elevated suggesting myocardial necrosis. The combined endpoint of MI and death was similar in groups 2 and 3 (50.3 vs. 51.9%, respectively, P = NS), which was significantly more than group 1 patients (35.6%, P < 0.01) over the follow-up period. Multivariate analysis of patients in groups 1 and 2 demonstrated that troponin microleak was an independent predictor of MI and death (P = 0.01). Microleak of troponin following elective PCI suggests myocardial injury and predicts an increased risk of subsequent MI and death. Troponins should be routinely assessed following PCI, and preventive therapies are needed to reduce micro and macro troponin elevation in the PCI setting.

A New Season for Cardiac Troponin Assays: It’s Time to Keep a Scorecard

Advancements in cardiac troponin (cTn)1 assay technology have created a conundrum for clinicians and laboratory scientists, who must determine which assays are best for optimal patient care. Unfortunately, few resources are available to guide the medical and scientific communities in this regard. International guidelines (1)(2)(3) have defined an increased cTn above the 99th percentile limit as an abnormal result; what is lacking, unfortunately, is an approach to define this limit across the heterogeneity of the assays. In spite of the evidence-based literature demonstrating that cTn concentrations tend to increase in individuals >60 years old (4), 99th percentile reference limits are often determined across wide age ranges using subjects as old as 70 years (convenience samples). Further frustrating the problem of selecting relevant reference subjects, in clinically defined “normal” individuals without known cardiovascular disease, increased cTn concentrations are indicative of a significantly higher risk of death (4)(5). The occurrence of such individuals in reference populations may reflect inadequate screening for comorbidities at the time of sample acquisition. Given such problems, a majority of laboratories either accept the manufacturer’s reference limit from the US Food and Drug Administration (FDA)-cleared package insert, perform an underpowered normal range study to establish a reference limit, or accept a reference limit published in the literature. To validate cTn assays, however—to level the playing field for all users—is necessary for the best patient care. cTnI and cTnT are established as the standard biomarkers for the detection of myocardial injury and prognostic evaluation of patients with acute coronary syndrome (ACS) and without (1)(2)(3). The consensus guidelines from the Global Task Force for the Universal Definition of Myocardial Infarction (1) and the National Academy of Clinical Biochemistry (2), plus the updated American College of Cardiology/American Heart Association guidelines …

Assay-related issues in the measurement of cardiac troponins

The recently released document by the Global Task Force on the universal definition of myocardial infarction (MI) has strengthened the role of cardiac troponin increase as the main criterion for MI diagnosis. Despite this pivotal role in clinical decisions, a number of assay-related issues can still markedly affect the test performance in the everyday practice. Regarding imprecision and analytical sensitivity, the performance of commercial assays is variable. Moreover, at least for troponin I, there is a lack of standardization among assay results. Appropriate cut points (99th percentile limit of the reference value distribution and/or 10% CV concentration value) can be established only if the assay performance is known and taken into account. Key characteristics to be defined include characterization by appropriate experimental and statistical protocols of the assay detection limit, total imprecision, and definition of the 99th percentile limit of the reference population. The widespread introduction of cardiac troponin measurements is an undoubted improvement, but some performance differences still exist with commercial assays, which most clinicians are unaware of and may give rise to wrong marker interpretation.

A critical appraisal of experimental factors influencing the definition of the 99th percentile limit for cardiac troponins

The recently released document by the Global Task Force on the "universal" definition of myocardial infarction (MI) recommends a single decision limit for cardiac troponin (cTn) corresponding to the 99th percentile limit of the reference value distribution [99th upper reference limit (URL)] for the diagnosis of patients presenting with suspected MI. However, use of this cut-off concentration posed a problem because most assays do not have the sensitivity to consistently measure cTn in the blood of apparently healthy individuals, with a high proportion of the values being below the method's detection limit. In addition to the influence of assay sensitivity, the 99th URL for cTn can vary depending on the reference population used, and its sample size. A marked difference can also be observed between the 99th URL obtained using plasma vs. that obtained with serum. Finally, some interferences with cTn measurement (e.g., by heterophile antibodies) may become more noticeable using assays that have increased analytical sensitivity that measure lower concentrations of these markers. In conclusion, a number of issues can markedly influence the definition of the 99th URL for cTn, which most clinicians are unaware of and may markedly condition the clinical performance of the test in routine practice.

Evaluation of analytical performance of the Pathfast® cardiac troponin I

Cardiac troponins are considered the cornerstone for risk stratification and diagnosis of patients with acute coronary syndrome (ACS). Following Clinical Laboratory Standards Institute (CLSI) guidelines, we assessed the analytical performances of the Pathfast (Mitsubishi, Japan) cTnI method. We evaluated different sample types. Control materials and lithium heparin plasma pools were used to determine: limit of blank (LoB), limit of detection (LoD), imprecision and linearity. The effects of potential endogenous interfering substances and the possibility of falsely increased cardiac troponin I (cTnI) concentrations attributable to the presence of heterophilic antibodies (HA), rheumatoid factor (RF) and human anti-mouse antibodies (HAMA) in high concentrations were evaluated. The 99th percentile limit of the cTnI value distribution was determined from 320 Caucasian reference individuals. No significant differences were found when cTnI concentrations of 40 lithium-heparin plasma samples were compared with the matched values of K(2)-EDTA plasma, whole blood and serum samples. The LoB and the LoD of the cTnI method were 0.0048 and 0.0066 microg/L, respectively. cTnI mean values from 0.66 to 6.0 microg/L showed a total CV% from 6.0 to 6.4. cTnI at a concentration of 0.02 microg/L was associated with a total CV of 9.6%. The method gave a linear response for cTnI concentrations within the measurement range. In six of 12 samples containing HA, a positive interference was demonstrated. The 99th percentile limit of the cTnI distribution in the reference population was 0.013 microg/L. The data indicate that the cTnI Pathfast method may be suitable for helping clinicians in the management of patients with ACS.

Performance of the Advia Centaur second-generation troponin assay TnI-Ultra compared with the first-generation cTnI assay

A cardiac troponin concentration above the 99th percentile limit of a reference population is a sensitive marker of myocardial necrosis. Current guidelines require troponin assays to have a total imprecision of < or =10% at the 99th percentile limit. In this study, the Advia Centaur second-generation TnI-Ultra assay was validated and compared with its predecessor the cardiac troponin I (cTnI) assay, with a focus on the current guidelines for diagnosis of acute myocardial damage. An imprecision profile of the TnI-Ultra assay was evaluated by analysing different pools over 20 days. The imprecision of the cTnI assay was used as comparison. The reference range was established based on TnI-Ultra analysis in 221 individuals. The cTnI concentration that could be determined with a total imprecision of 10% was 0.05 microg/L for the TnI-Ultra assay and 0.3 microg/L for the cTnI assay. The 99th percentile limit in the distribution of a reference population was 0.06 microg/L as determined with the TnI-Ultra assay. The TnI-Ultra assay provides significantly improved sensitivity when compared with the cTnI assay and a total imprecision of < or =10% is obtained at the 99th percentile limit of value distribution of a reference population. Using the TnI-Ultra assay, slightly increased cTnI concentration can be detected reliably following the current guidelines.

Validation of the 99th Percentile Cutoff Independent of Assay Imprecision (CV) for Cardiac Troponin Monitoring for Ruling Out Myocardial Infarction

By definition, the probability that a single measured cardiac troponin result exceeds the estimated 99th percentile is equal to 0.01 (1%) for a person randomly selected from the general (reference) population. This is irrespective of the imprecision profile of the analytical method as well as the lack of standardization of cardiac troponin assays (1)(2)(3)(4)(5)(6)(7). However, the probability that a measured result exceeds the 99th percentile limit for a specific person from the reference population will vary depending on that person’s true concentration and on the imprecision profile of the specific analytical method. Furthermore, the overall probability that at least one of multiple measured values (the second or third measured cardiac troponin concentration in a timed series of cardiac troponin orders) exceeds the 99th percentile also will vary depending on the imprecision of the analytical method. To investigate the influence of assay imprecision on the likelihood of misclassifying healthy individuals or patients without myocardial injury, we simulated the distribution of cardiac troponin I (cTnI) results in a general population and added random analytical error reflecting different assay imprecision profiles. One imprecision profile assumes a CV of 37.5% at a cTnI of 0.05 μg/L, decreasing to a CV of 25% at a cTnI of 0.07 μg/L, …