False-positive troponin I measured with the Abbott AxSYM attributed to fibrin interference

Cardiac troponin

Cardiac troponin (cTn) testing plays a crucial role in the diagnosis of cardiovascular diseases, particularly acute coronary syndrome (ACS), which includes acute myocardial infarction (AMI). However, conventional immunoassays may be subject to interference from autoantibodies, cross-reactivity, and biotin-related effects, compromising diagnostic accuracy. A thorough investigation of these interference mechanisms is necessary to improve assay methodologies, ensuring greater reliability and precision. In recent years, significant advancements in mass spectrometry (MS) technology have sparked increased interest in its application for cTn testing. For instance, liquid chromatography-tandem mass spectrometry (LC-MS/MS) employs multiple reaction monitoring (MRM) to accurately quantify cardiac troponin I (cTnI)-specific tryptic peptides along with their fragment ions. This technique effectively reduces immunoassay interference while improving analytical specificity. Compared to traditional immunoassays, MS-based approaches alleviate matrix effects and analytical interferences while achieving superior specificity. Nonetheless, clinical adoption remains constrained by technical complexity; thus clinicians can obtain more reliable diagnostic insights. This review summarizes the current landscape of cTn detection technologies by examining the prevalence of false-positive results across various methods. It further explores both the practical applications and challenges associated with MS-based techniques in cTn testing. Ultimately, this review aims to improve cTn testing reliability, enhance cardiovascular disease diagnosis, and guide personalized treatment strategies.

Role of Antitroponin Antibodies and Macrotroponin in the Clinical Interpretation of Cardiac Troponin

Cardiac troponin is extensively used as a biomarker in modern medicine due to its diagnostic capability for myocardial injury, as well as its predictive and prognostic value for cardiac diseases. However, heterophile antibodies, antitroponin antibodies, and macrotroponin complexes can be observed both in seemingly healthy individuals and patients with cardiac diseases, potentially leading to false positive or disproportionate elevation of cTn (cardiac troponin) assay results and introducing discrepancies in clinical interpretations with impact on medical management. In this review article, we describe the possible mechanisms of cTn release and the sources of variations in the assessment of circulating cTn levels. We also explore the pathophysiological mechanisms underlying antitroponin antibody development and discuss the influence exerted by macrotroponin complexes on the results of immunoassays. Additionally, we explore approaches to detect these complexes by presenting various clinical scenarios encountered in routine clinical practice. Finally, unsolved questions about the development, prevalence, and clinical significance of cardiac autoantibodies are discussed.

Retrospective analysis of intra-patient laboratory variation demonstrates that the BD Vacutainer® Barricor™ blood collection tube reduces troponin variation

OBJECTIVE

The BD Vacutainer® Barricor™ plasma blood collection tube uses a mechanical separator during centrifugation to separate plasma from the cellular elements of blood. Compared to use of plasma separator tubes (PST™) with gel, Barricor™ produces a cleaner sample with less residual cellular content. We sought to determine if Barricor™ reduces pre-analytical error compared to PST™.

DESIGN & METHODS

We used a model previously published that utilizes serial differences between intra-patient measurements transformed into a Taylor series of variation vs time with the y-intercept equal to the sum of short-term analytic variation, preanalytic variation and biologic variation. The intra-patient variation of chloride, sodium, potassium, and troponin-T (hs-TnT) obtained from the Emergency Department of a large tertiary care center sampled with PST™ (May 2015-April 2018, n = 59,762 specimens) or Barricor™ (May 2018-May 2021, n = 61,512 specimens) was evaluated. All specimens were analyzed on either Roche Modular or Cobas® instruments. For each analyte, pairs of intra-patient results were tabulated and separated by 1 h intervals. The average between-pair variations were then regressed against time. We also determined the number of intra-patient outliers using the reference change value for each analyte.

RESULTS

The Barricor™ hs-TnT y-intercept (-0.0132) was significantly lower than the PST™ intercept (0.9109; p = 0.022). This was also true for chloride (y-intercept = 1.0067 in Barricor™ and 1.3431 in PST™, p = 0.037). The percentage of hs-TnT outliers was significantly lower in Barricor™ (8.32 %) vs PST™ (12.2 %; p < 0.001).

CONCLUSION

The analytical and biological variations are assumed to be steady over the study periods; we ascribe the difference in the y-intercept to the preanalytical effect of the Barricor™ tube reducing platelets and other cellular debris.

Falsely elevated thyroid hormone levels associated with fibrin interference in patients receiving oral anticoagulant therapy

OBJECTIVE

Unique clinical courses were observed in two asymptomatic patients receiving warfarin who referred to our hospital because of suspected central hyperthyroidism. We eventually diagnosed these patients with falsely elevated thyroid hormone levels caused by macroscopically invisible fibrin. Although false results caused by fibrin interference in vitro have been identified in various immunoassays, especially in blood samples from patients receiving anticoagulant therapy, no studies on thyroid function testing have been reported. The experience in evaluating these cases prompted us to investigate the independent influence of oral anticoagulants via putative fibrin interference on thyroid function testing.

METHODS

We retrospectively reviewed known contributing factors that affect thyroid function testing including age, gender, medication history, body mass index, estimated glomerular filtration rate, smoking status, alcohol consumption, and the seasons of hospital visits from participants who presented the Department of Health Checkup between April 2010 and December 2020.

RESULTS

A propensity-matched analysis revealed that the median serum free thyroxine levels under oral anticoagulant were significantly higher (17.9 pmol/L, n = 60) than those without anticoagulants (16.0 pmol/L, n = 60; p < 0.001). It was noted that this difference was the largest among contributing factors we analyzed. No significant differences were noted in serum thyroid-stimulating hormone levels.

CONCLUSIONS

We report two patients receiving warfarin with falsely elevated thyroid hormone levels caused by fibrin interference resembling central hyperthyroidism for the first time. Our retrospective study suggests that the medication status of oral anticoagulants should be considered when evaluating thyroid function tests.

Not T too! False elevations in high-sensitivity cardiac troponin T (hs-TnT) following specimen transport

Though false elevations attributed to preanalytical specimen handling have been widely reported for Troponin I (TnI), Troponin T (TnT) has appeared more robust to falsely elevated Tn. We describe reproducible false elevations in high sensitivity TnT (hs-TnT) in specimens after courier transport in plasma separator tubes (PST) off-site for testing. Hs-TnT was measured under 5 different conditions: 1) at collection location (N=24); 2) after transport upright in racks (N=66); 3) after transport with no control over tube agitation (N=69); 4) on transported aliquots (N=84); or 5) immediately after transport with no control over tube agitation (N=16), followed by keeping the specimen upright and re-measuring at 1hr, 2hr, 4hr, and 20-24hrs (N=6). To assess the degree of discrepancy, plasma from the original PST was aliquotted, re-centrifuged, potential debris removed, and hs-TnT re-measured. 43% of PST specimens collected offsite and transported with no control over tube agitation had clinically significant false elevations of hs-TnT which subsequently decreased following aliquotting and re-centrifugation (median decrease =9.9ng/L). Onsite testing or transported aliquots demonstrated no discrepancy. After being kept upright, discrepant specimens were not different from re-centrifuged aliquots by 4hrs (p=0.6141, repeated measures ANOVA with Dunn's multiple comparisons). Clinically significant false elevations of hs-TnT occurred in approximately 40% of separated PSTs that were transported in containers where specimens are transported with no control over tube agitation. This interference does not occur if plasma is aliquoted or if hs-TnT is tested at the collection site. In order to prevent these false elevations, and their potential patient impact on the diagnosis of acute myocardial infarction, specimens for hs-TnT measurement should be aliquoted at the collection location prior to transport.

Analytical and Clinical Considerations in Implementing the Roche Elecsys Troponin T Gen 5 STAT Assay

OBJECTIVES

To evaluate the analytical and clinical performance characteristics of the fifth-generation troponin T reagent.

METHODS

Troponin T was measured in 2,332 paired serum and plasma samples from emergency department and hospital patients using the fourth- and fifth-generation reagents. Testing was repeated after recentrifugation to determine the frequency of analytical outliers and percentage of patients with elevated values for each assay. We conducted separate experiments to determine the effects of biotin and hemolysis interference, as well as measure interinstrument variability, for fifth-generation troponin T.

RESULTS

Analytic outliers occurred more frequently using the fifth-generation reagent (3.4%) compared with the fourth-generation reagent (1.0%). The frequency of elevated troponin T above the 99th percentile upper reference limit was 26% for the fourth-generation reagent and 52% for the fifth-generation reagent. Clinically significant assay interference by biotin was observed at 20 ng/mL, but hemolysis interference was not observed until an H index of 150. Instrument-to-instrument variability between e411 and e601/602 instrument platforms is predicted to confound clinical interpretation of troponin changes.

CONCLUSIONS

Analytical outliers and instrument-to-instrument variability are the two analytical variables most likely to confound interpretation of changes in fifth-generation troponin T results over time.

Troponin interference with special regard to macrocomplex formation

Biomarkers, such as troponin-T and troponin-I, are regarded as the gold standard laboratory parameter for diagnosing many cardiological diseases. These parameters have been approved for clinical use. Many cardiological guidelines recommend the analysis of troponins in the majority of cardiological disease diagnoses and to also gain prognostic information. Nonetheless, many medical circumstances could cause false troponin elevations. In this article, we focus on troponin artifacts, particularly macro-immune complex formation, as important interference factors. Therefore, we performed a literature search from 2006 to 06/2021.

Serum or plasma? An old question looking for new answers

Serum or plasma? An old question looking for new answers. There is a continual debate on what type of sample a clinical laboratory should use. While serum is still considered the gold standard and remains the required sample for some assays, laboratories must consider turn-around time, which is an important metric for laboratory performance and, more importantly, plays a critical role in patient care. In addition, a body of evidence emphasise the choice of plasma in order to prevent modifications of some analytes due to the coagulation process and related interferences. Advantages and disadvantages of serum and plasma are discussed on the basis of current literature and evidence. In addition, data are provided on the current utilisation of the samples (serum or plasma) in Italy and in other countries. Finally, a rationale for a possible switch from serum to plasma is provided.

Potential false-positive reasons for SARS-CoV-2 antibody testing and its solution

Coronavirus disease 2019 (COVID-19) has brought a huge impact on global health and the economy. Early diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is essential for epidemic prevention and control. The detection of SARS-CoV-2 antibodies is an important criterion for diagnosing COVID-19. However, SARS-CoV-2 antibody testing also has certain false positives causing confusion in clinical diagnosis. This article summarizes the causes of false-positive detection of SARS-CoV-2 antibodies in clinical practice. The results indicate that the most common endogenous interferences include rheumatoid factor, heterophile antibodies, human anti-animal antibodies, lysozyme, complement, and cross-antigens. The exogenous interference is mainly incomplete coagulation of the specimen, contamination of the specimen, and insufficient optimization of the diagnostic kit's reaction system.

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.

Different Re-centrifugation Conditions for Infectious Disease Screening Using the Abbott I2000

We investigated whether an ordinary centrifuge can achieve the standard centrifugal effect required according to specifications for infectious disease screening using the Abbott i2000. Samples were collected and centrifuged following a standard operating procedure (SOP). They were then divided into three groups according to the results of the initial screening tests: a negative group, weak-positive group, and positive group. Twenty negative samples and all weak-positive and positive samples were re-analyzed. Two tubes for each re-analyzed sample were centrifuged simultaneously, one for 10 min at 10 000 × g, per recommendations, and one for 10 min at 2750 × g. No significant difference was found between the groups using different centrifugal forces. There was a strong correlation in the quantitative values between the two conditions of centrifugation. Consistency analysis showed a Cronbach's alpha > 0.8 for detection of Treponema pallidum, human immunodeficiency virus (HIV), hepatitis C virus (HCV), and hepatitis B surface antigen in the three groups (negative group, weak-positive group, and positive group) under different centrifugation conditions. Strong consistency was found under different centrifugal conditions, regardless of the initial testing results. In conclusion, we conducted centrifugation steps in duplicate, according to infectious disease screening protocols. Our study showed that all samples should be centrifuged using a recommended relative centrifugal force after a proper clotting time, as in the standard operating procedure of our laboratory. In this way, we were able to obtain the same results using an ordinary centrifuge as those obtained using a high-speed centrifuge, such as the Abbott i2000.

Integrity of serum samples is changed by modified centrifugation conditions

Background Serum samples should be centrifuged for at least 10 min at 1300-2500 × g. Changed centrifugation conditions could compromise sample quality. The objective of this study was to compare the serum quality and turnaround time (TAT) using different centrifugation conditions. Methods The study was done in four different periods (A, B, C and D) at different conditions: for 10, 5 and 7 (A, B and C, respectively) at 2876 × g, and 7 (D) min at 4141 × g. Sample quality was assessed as the proportion of samples with: (a) aspiration errors, (b) H index >0.5 g/L and (c) suppressed reports of potassium (K) due to hemolysis. TAT was calculated for emergency samples. The proportions of samples (a), (b) and (c) were compared according to period A. Results The number of aspiration errors was significantly higher in samples centrifuged at 2876 × g for 5 min (p = 0.021) and remained unchanged when centrifuged for 7 min (p = 0.066 and 0.177, for periods C and D, respectively). In periods B, C and D, the proportion of samples with hemolysis was higher than that in period A (p-values 0.039, 0.009 and 0.042, respectively). TAT differed between all periods (p < 0.001), with the lowest TAT observed for B and D. The lowest number of samples exceeding 60-min TAT was observed in period D (p = 0.011). Conclusions The integrity of serum samples is changed with different centrifugation conditions than those recommended. Our study showed that shorter centrifugation at higher force (7 min at 4141 × g) significantly decreases TAT, with unchanged proportion of samples with aspiration errors.

False-positive TSH receptor antibody-a pitfall of third-generation TSH receptor antibody measurements in neonates

Maternal Graves' disease (GD) during pregnancy may influence thyroid function in fetuses. Neonates born to mothers with high serum TSH receptor antibody (TRAb) levels have been reported to develop 'neonatal GD'. Therefore, evaluations of serum thyroid hormone and TRAb levels in neonates upon birth are crucial for a prompt diagnosis. At delivery, we measured TRAb with third-generation TRAb test using an M22 human monoclonal antibody in neonates by collecting umbilical cord blood in a blood collection tube with lithium-heparin, which provides a whole blood/plasma sample. In recent years, we have encountered positive TRAb levels (more than 2.0 IU/L) in nineteen neonates born to mothers with GD whose thyroid hormone levels were almost within the reference range and serum TRAb levels were less than 10 IU/L. All the neonates with positive TRAb levels did not exhibit thyrotoxicosis. However, when we measured TRAb levels with serum sample in six out of the nineteen cases, their serum TRAb levels were all negative, suggesting a discrepancy of TRAb levels between in lithium-heparin plasma from umbilical cord blood and serum. Moreover, this discrepancy was observed in neonates born to euthyroid mothers, adult active GD patients and healthy volunteers. Since lithium-heparin plasma from umbilical cord blood is widely used in laboratory tests at delivery, we may encounter 'false-positive' TRAb, which may, in turn, lead to a misdiagnosis of neonatal GD. This is a pitfall of third-generation TRAb measurements in neonates, particularly at delivery, and needs to be considered by obstetricians and neonatologists.

The BD Barricor blood collection tube is an acceptable and robust alternative to the PST for use with the Beckman AccuTnI+3 assay

OBJECTIVES

BD Canada recently released a blood collection tube with a novel mechanical separator called the Barricor. We evaluated this tube as an alternate sample type for cardiac troponin I (cTnI) testing using the Beckman Coulter AccuTnI+3 assay.

DESIGN AND METHODS

3014 paired patient specimens (Barricor, plasma separator tube or PST) were obtained from the emergency departments and cardiac care units of nine hospitals in and around Edmonton, Alberta. After centrifugation, each plasma sample was analyzed for cTnI using the Beckman Coulter AccuTnI+3 assay. In addition, selected samples were analyzed multiple times within a single run or over 4-5days to generate imprecision data for the assay.

RESULTS

Repeatability and within-laboratory studies revealed an imprecision of <10% at concentrations above 0.025μg/L for the Barricor as well as BD's traditional PST. Paired patient sample comparisons over the full range of the assay yielded linear regression slopes ranging from 0.956 to 1.011 and Pearson correlation coefficients ranging from 0.993 to 0.999. At a lower range of results closer to the manufacturer's 99th percentile cutoffs correlation was slightly worse, but still acceptable, with linear regression slopes ranging from 0.967 to 1.211 and Pearson correlation coefficients ranging from 0.983 to 0.987. Notably, at these lower concentrations the agreement between individual PST and Barricor results worsened with decreasing cTnI concentration. Differences between pairs of results became particularly large (-50 to +400%) at PST cTnI concentrations ≤0.015μg/L. Closer inspection of the data around the 0.02 and 0.04μg/L 99th percentile cutoffs revealed a number of discordances between PST and Barricor results, with at least some of these attributable to false elevations in the PST results.

CONCLUSIONS

Together, our results suggest that the Barricor blood collection tube is good alternative to the traditional PST for cTnI testing using the AccuTnI+3 assay. The Barricor appears to minimize spurious, nonreproducible, and false elevations in cTnI results for a subset of patients but additional studies are needed to determine if it reduces overall false elevations. cTnI results below 0.04μg/L may still be of questionable accuracy even with the use of this new tube.

Recovery of spiked troponin I in four routine assays

Introduction

This study aimed to examine the recovery of spiked human cardiac troponin I (cTnI) results measured by four routine assays, and investigate possible interference from microclots.

Materials and methods

457 consecutive samples with cTnI concentration below limit of quantitation (12 ng/L), declared by the Vitros TnI ES assay (reference assay), were measured on Beckman Coulter Accu TnI+3, Siemens TnI-Ultra and Roche TnI STAT assays. These samples were enriched with native full-length cTnI to a concentration of 100 ng/L and retested. A post-spiking result that exceeded the critical difference at a predefined probability of 0.0005 of the target concentration (the median post-spiking result for each individual assay) was considered as outlier. To determine whether microclots were a significant cause of critically discrepant outlier results, a separate 50 samples were centrifuged twice between two post-spiking measurements using the Vitros TnI ES assay.

Results

The median recovery of the enriched cTnI was highest with the Roche assay (271 ng/L) and lowest with the Vitros assay (29 ng/L). The Vitros assay had the highest percentage of results that exceeded the critical difference (49%), followed by the Siemens (38%), Roche (18%) and Beckman Coulter (7%) assays. None of the 50 additional samples produced a critically lower cTnI result after re-centrifugation.

Conclusions

Our findings underscored the variability of cTnI assays in measuring native cTnI. The lack of cTnI results that became significantly lower after re-centrifugation suggested that microclots are unlikely to be a major cause of the outlier results.

Troponin assays in the assessment of the equine myocardium

In 2000, troponin assays were adopted as the test of choice for detection of myocardial injury in man. This decision was made after extensive testing and followed a 60 year search for a biomarker of myocardial damage with sufficient analytical sensitivity and specificity. This has led to proliferation of assays for use in human medicine, each requiring extensive testing and validation before it could be made available on the open market for human use. The search for ever-more analytically sensitive assays and for a standard reference material continues. The adoption of troponin testing in veterinary medicine followed shortly after its development for use in man, providing a much-needed means of detecting and monitoring myocardial damage in horses. However, application of these tests in veterinary medicine has exclusively involved use of assays designed for and clinically validated in human patients. There is no mandated requirement for test validation in veterinary medicine and, while many of these assays have been shown to be capable of detecting equine troponin, the wide diversity of available tests, lack of validation, absence of protocols for their use and lack of standardisation make their application problematic. The objective of this review article is to address this issue, offering guidance where data are available and encouraging caution where there are none. Ultimately, the overall goal of this review is to examine critically the use of troponin assays in the horse and to promote the accurate and appropriate interpretation of valid results.

Outliers affecting cardiac troponin I measurement: comparison of a new high sensitivity assay with a contemporary assay on the Abbott ARCHITECT analyser

Background

False-positive cardiac troponin (Tn) results caused by outliers have been reported on various analytical platforms. We have compared the precision profile and outlier rate of the Abbott Diagnostics contemporary troponin I (TnI) assay with their high sensitivity (hs) TnI assay.

Methods

Three studies were conducted over a 10-month period using routine patients’ samples. TnI was measured in duplicate using the contemporary TnI assay in Study 1 and Study 2 ( n = 7011 and 7089) and the hs–TnI assay in Study 3 ( n = 1522). Critical outliers were defined as duplicate results whose absolute difference exceeded a critical difference (CD =  z x √2 x SDAnalytical) at a probability level of 0.0005, with one of the results on the opposite side of the decision limit to its partner.

Results

The TnI concentration at 10% imprecision (coefficient of variation) for the contemporary TnI assay was 0.034 µg/L (Study 1) and 0.042 µg/L (Study 2), and 0.006 µg/L (6 ng/L) for the hs–TnI assay. The critical outlier rates for the contemporary TnI assay were 0.51% (Study 1) and 0.37% (Study 2) using a cut-off of 0.04 µg/L, and 0% for the hs–TnI assay using gender-specific cut-offs.

Conclusion

The significant number of critical outliers detected using the contemporary TnI assay may pose a risk for misclassification of patients. By contrast, no critical outliers were detected using the hs–TnI assay. However, the total outlier rates for both assays were significantly higher than the expected variability of either assay. The cause of these outliers remains unclear.

Clinical review: improving the measurement of serum thyroglobulin with mass spectrometry

CONTEXT

Serum thyroglobulin (Tg) measurements are central to the management of patients treated for differentiated thyroid carcinoma. For decades, Tg measurements have relied on methods that are subject to interference by commonly found substances in human serum and plasma, such as Tg autoantibodies. As a result, many patients need additional imaging studies to rule out cancer persistence or recurrence that could be avoided with more sensitive and specific testing methods.

OBJECTIVES

The aims of this review are to: 1) briefly review the interferences common to Tg immunoassays; 2) introduce readers to liquid chromatography-tandem mass spectrometry as a method for quantifying proteins in human serum/plasma; and 3) discuss the potential benefits and limitations of the method in the quantification of serum Tg.

RESULTS

Mass spectrometric methods have traditionally lacked the sensitivity, robustness, and throughput to be useful clinical assays. These methods failed to meet the necessary clinical benchmarks due to the nature of the mass spectrometry workflow and instrumentation. Over the past few years, there have been major advances in reagents, automation, and instrumentation for the quantification of proteins using mass spectrometry. More recently, methods using mass spectrometry to detect and quantify Tg have been developed and are of sufficient quality to be used in the management of patients.

CONCLUSIONS

Novel serum Tg assays that use mass spectrometry may avoid the issue of autoantibody interference and other problems with currently available immunoassays for Tg. Prospective studies are needed to fully understand the potential benefits of novel Tg assays to patients and care providers.

Probing indiscretions: contamination of cardiac troponin reagent by very high patient samples causes false-positive results

Background

Cardiac troponin (cTn) has become the standard biomarker for the diagnosis of acute coronary syndromes. False-positive cTnI results have previously been reported on the Beckman Coulter analysers, which were shown to be random, not reproducible and occurred more commonly than expected. Our investigation ensued after a patient sample with an inordinately elevated cTnI was analysed, followed by a series of false-positive results being reported. The implications of falsely elevated cTnI results on patient care could be considerable.

Methods

Multiple experiments with patient sample pools with concentrations below the 99th percentile to extremely high (0.025, 15, 175 and 884 μg/L) were conducted in varying sequences of high and low samples on the Beckman Coulter Access2, UniCel DxI600 and UniCel DxI800 analysers.

Results

Our results demonstrate a significant increase in cTnI concentrations in the negative pool after analysis of high pool samples in various sequences. This increase is sufficient to cause elevations above the 99th percentile cut-off and false-positive cTnI results. These findings were reproducible on all three analysers.

Conclusions

Our study is highly suggestive of carryover and cTnI reagent pack contamination by the pipettors on the Access2, DxI600 and DxI800 analysers when patient samples with extremely high cTnI concentrations are analysed, leading to potential false-positive cTnI results on subsequent samples.

BD rapid serum tubes reduce false positive plasma troponin T results on the Roche Cobas e411 analyzer

OBJECTIVES

In an attempt to reduce false positive results and improve turnaround time, we investigated the BD Rapid Serum Tube as an alternate sample type to lithium heparin plasma for Roche Troponin T analysis on the Roche Cobas e411 analyzer.

DESIGN AND METHODS

BD Plasma Separator Tubes (PST) and Rapid Serum Tubes (RST) were collected in tandem from Emergency Department patients who had clinical orders for Troponin T over a 1 month period.

RESULTS

RST and PST samples yielded analytically and clinically concordant Troponin T results on the Roche Cobas e411. Rare false positive results in lithium heparin samples were not observed with rapid clot serum tubes.

CONCLUSIONS

RST samples are appropriate for stat Troponin T analysis, and appear to reduce the incidence of rare false positive Troponin T results obtained with lithium heparin samples.

Use of the BD vacutainer rapid serum tube reduces false-positive results for selected beckman coulter Unicel DxI immunoassays

We investigated the use of serum samples from BD Vacutainer rapid serum tubes (RSTs; BD, Franklin Lakes, NJ) to reduce undetermined interferences contributing to false-positive immunoassay results in heparin plasma samples. Patients being evaluated for suspected myocardial infarction had specimens drawn into an RST in addition to the standard lithium-heparin plasma separator tube (PST). We measured 28 separate analytes in both specimens using immunoassay, electrochemical, and spectrophotometric methods. Higher results were observed in some PST specimens tested for troponin I, creatine kinase-MB isoenzyme, human chorionic gonadotropin, and thyroid-stimulating hormone. These discrepancies were investigated by repeating analyses after recentrifugation of both specimens. Reanalysis gave results for the PST specimens that were lower and agreed well with initial results from RSTs, suggesting false-positive rates of 10.8% for troponin I and about 2% for each of the other 3 analytes. Overall, specimens collected in RSTs had fewer false-positive immunoassay results than specimens collected in plasma separator tubes.

Outliers as a Cause of False Cardiac Troponin Results: Investigating the Robustness of 4 Contemporary Assays

BACKGROUND

It is important that cardiac troponin be measured accurately with a robust method to limit false results with potentially adverse clinical outcomes. In this study, we characterized the robustness of 4 analytical platforms by measuring the outlier rate between duplicate results.

METHODS

We measured cardiac troponin concurrently in duplicate with 4 analyzers on 2391 samples. The outliers were detected from the difference between duplicate results and by calculating a z value: z = (result 1 − result 2) ÷ √(SD1est2 + SD2est2), with z &gt; 3.48 identifying outliers with a probability of 0.0005.

RESULTS

The outlier rates were as follows: Abbott Architect i2000SR STAT Troponin-I, 0.10% (0.01%–0.19%); Beckman Coulter Access2 Enhanced AccuTnI, 0.44% (0.25%–0.63%); Roche Cobas e601 TroponinT hs, 0.06% (0.00%–0.13%); and Siemens ADVIA Centaur XP TnI-Ultra, 0.10% (0.01%–0.19%). The occurrence of outliers was higher than statistically expected on all platforms except the Cobas e601 (χ2 = 2.7; P = 0.10). A conservative approach with a constant 10% CV and z &gt; 5.0 identified outliers with clear clinical impact and resulted in outlier rates of 0.11% (0.02%–0.20%) with the Architect i2000SR STAT Troponin-I, 0.36% (0.19%–0.53%) with the Access2 Enhanced AccuTnI, 0.02% (0.00%–0.06%) with the Cobas e601 TroponinT hs, and 0.06% (0.00%–0.13%) with the ADVIA Centaur XP TnI-Ultra.

CONCLUSIONS

Outliers occurred on all analytical platforms, at different rates. Clinicians should be made aware by their laboratory colleagues of the existence of outliers and the rate at which they occur.

Falsely elevated troponin I results due to outliers indicate a lack of analytical robustness

Aims

Troponin (Tn) is the preferred biochemical marker for the diagnosis of acute coronary syndrome. Spurious false Tn results (outliers) may cause significant problems with clinical management. We investigated the occurrence of outliers and whether this phenomenon could be explained by analytical imprecision.

Methods and results

Troponin I (TnI) was measured in duplicate with Beckman AccuTnI reagent if the first TnI result was ≥0.04 μg/L ( n = 5265). All TnI requests were performed in duplicate in a subset of samples for one calendar month ( n = 881). A total of 13,178 TnI requests were received during the study period. Variables were sample type, centrifugation speed and analyser. Results were identified as outliers when the difference between two results exceeded a critical difference (CD) limit defined by CD = z × √2 × SDAnalytical. Outliers at the 0.0005 probability level were detected in 102 of 5265 duplicate observations (1.94 ± 0.37%). This translated into an outlier rate of 0.55 ± 0.13% for all TnI results and 1.37 ± 0.31% for results above 0.04 μg/L. Outliers resulted only in falsely elevated TnI values and were not dependent on the analyser, centrifugation speed or sample type.

Conclusion

TnI outliers occurred more frequently than anticipated, could not be explained by analytical imprecision and indicated a lack of robustness in the assay. The high rate and the magnitude of the errors will complicate clinical management and carry a risk of detrimental patient outcome. The outlier rate is a useful parameter to define the robustness of assays.

Subclinical myocardial necrosis and cardiovascular risk in stable patients undergoing elective cardiac evaluation

OBJECTIVE

The presence of subclinical myocardial necrosis as a prodrome to longer-term adverse cardiac event risk has been debated. The debate has focused predominantly within patients with acute coronary syndrome, and on issues of troponin assay variability and accuracy of detection, rather than on the clinical significance of the presence of subclinical myocardial necrosis (ie, "troponin leak") within stable cardiac patients. Herein, we examine the relationship between different degrees of subclinical myocardial necrosis and long-term adverse clinical outcomes within a stable cardiac patient population with essentially normal renal function.

METHODS AND RESULTS

Sequential consenting patients (N=3828; median creatinine clearance, 100 mL/min/1.73m(2)) undergoing elective diagnostic coronary angiography with cardiac troponin I (cTnI) levels below the diagnostic cut-off for defining myocardial infarction (<0.03 ng/mL) were evaluated. The relationship of subclinical myocardial necrosis with incident major adverse cardiovascular events (defined as any death, myocardial infarction, or stroke) over 3-year follow-up was examined. "Probable" (cTnI 0.001-0.008 ng/mL) and "definite" (cTnI 0.009-0.029 ng/mL) subclinical myocardial necrosis were observed frequently within the cohort (34% and 18%, respectively). A linear relationship was observed between the magnitude of subclinical myocardial necrosis and risk of 3-year incident major adverse cardiovascular events, particularly in those with cTnI 0.009 ng/mL or higher (hazard ratio, 3.00; 95% confidence interval, 2.4-3.8), even after adjustment for traditional risk factors, C-reactive protein, and creatinine clearance. The presence of subclinical myocardial necrosis was associated with elevations in acute phase proteins (C-reactive protein, ceruloplasmin; P<0.01 each) and reduction in systemic antioxidant enzyme activities (arylesterase; P<0.01) but showed no significant associations with multiple specific measures of oxidant stress, and showed borderline associations with myeloperoxidase, a marker of leukocyte activation.

CONCLUSIONS

In stable cardiology patients, prodromal subclinical myocardial necrosis is associated with substantially higher long-term risk for major adverse cardiovascular events. The underlying mechanisms contributing to this minimal troponin leak phenomenon warrants further investigation.

The use of biomarkers for the evaluation and treatment of patients with acute coronary syndromes

The advent of inexpensive, highly accurate, and predictive markers of myocardial injury, inflammation, and hemodynamic stability has revolutionized the evaluation and treatment of patients who have acute coronary syndromes (ACSs). These blood biomarkers require small sample volumes, can be run expeditiously, and provide important information concerning the diagnosis, risk stratification, and treatment of these patients. To understand the use of these markers, one must have some knowledge about what elevations in these markers imply, how they have to be collected and measured to provide reliable information, when to suspect analytic confounds, and what the key values are that impart the diagnostic, prognostic, and therapeutic information. This article discusses these issues, emphasizing what clinicians must know for optimal test use, and then addresses the practical use of these markers in patients who have ACS.