An improved rapid troponin T test with a decreased detection limit: a multicentre study of the analytical and clinical performance in suspected myocardial damage

Cardiac biomarkers by point-of-care testing – back to the future?

The measurement of the cardiac troponins (cTn), cardiac troponin T (cTnT) and cardiac troponin I (cTnI) are integral to the management of patients with suspected acute coronary syndromes (ACS). Patients without clear electrocardiographic evidence of myocardial infarction require measurement of cTnT or cTnI. It therefore follows that a rapid turnaround time (TAT) combined with the immediacy of results return which is achieved by point-of-care testing (POCT) offers a substantial clinical benefit. Rapid results return plus immediate decision-making should translate into improved patient flow and improved therapeutic decision-making. The development of high sensitivity troponin assays offer significant clinical advantages. Diagnostic algorithms have been devised utilising very low cut-offs at first presentation and rapid sequential measurements based on admission and 3 h sampling, most recently with admission and 1 h sampling. Such troponin algorithms would be even more ideally suited to point-of-care testing as the TAT achieved by the diagnostic laboratory of typically 60 min corresponds to the sampling interval required by the clinician using the algorithm. However, the limits of detection and analytical imprecision required to utilise these algorithms is not yet met by any easy-to-use POCT systems.

The effect of elapsed time on cardiac troponin-T (cTnT) degradation and its dependency on the cause of death

PURPOSE

The aim of the present study is to evaluate the effect of elapsed time on cardiac troponin-T degradation and its dependency on the cause of death.

METHODS

The cases included in this study were divided into six groups depending upon the cause of death without any prior history of disease that died in the hospital and their exact time of death was known. The analysis involves extraction of the protein, separation by denaturing gel electrophoresis and visualization by Western blot.

RESULTS

Western blot data shows the rate of degradation of cTnT into lower molecular weight fragments with respect to time. In cases of control group the greatest amount of protein breakdown was observed within the first 64 h while in MI cases within first 6 h, the original band of cTnT (42 kDa) decreased markedly into seven major fragments, with 25 kDa & 20 kDa fragments being the most prominent. In burn group, at 41.40 h blot shows maximum fragmentation. In electrocution group the greatest amount of protein breakdown was observed within the first 50 Hrs. Within asphyxia cases, the original band of cTnT (42 kDa) decreased markedly into many major and minor fragments which continues up to 210 Hrs while the original band of cTnT (42 kDa) in poisoning cases decreased markedly into many major & minor fragments up to 140 h but after it blot shows only intact protein of very less intensity with few minor fragments.

CONCLUSION

It can be observed that in case of death due to MI, the intact cTnI fragmented at a much faster rate than in burn, electrocution, control, poisoning and asphyxia group. Thus, the rate of fragmentation of intact cTnT into lower molecular weight fragments depends upon the cause of death.

The effect of elapsed time on cardiac troponin-T (cTnT) degradation and its relation to postmortem interval in cases of electrocution

BACKGROUND

The estimation of postmortem interval (PMI) is of paramount importance for the police in their investigation when arriving at the scene of a questionable death. The aim of present study is to evaluate the effect of elapsed time on cardiac Troponin-T degradation and its association with PMI in cases of death due to electrocution.

METHODS

Cardiac tissue samples were collected from medico-legal autopsies, after informed consent from the relatives. The cases included were the subjects of electrocution without any prior history of disease who died in the hospital and their exact time of death was known. The analysis involves extraction of the protein at room temperature for different time periods (∼5, 26, 50, 84, 132, 157, 180, 205 and 230 Hrs), separation by SDS-PAGE and visualization by Western blot using cTnT specific monoclonal antibodies.

RESULTS

The results specify a characteristic banding pattern amongst human cadavers (n = 5), a pseudo-linear relationship between percent cTnT degraded and the time since death (R(2) = 0.87, p = 0.0001) was observed. The area of the bands within a lane was quantified by scanning and digitizing the image using Gel Doc (Universal Hood II).

CONCLUSIONS

The post-mortem Troponin-T fragmentation observed in this study reveals a sequential, time-dependent process with the potential for use as a predictor of PMI in cases of electrocution.

Comparison of the diagnostic performance of two rapid bedside biochemical assays in the early detection of acute myocardial infarction

BACKGROUND

New biochemical markers have been recently proposed as potential aids in the diagnosis of myocardial infarction. Assessment of these markers in real time by near-patient testing would allow more rapid decisions regarding critical therapeutic interventions.

HYPOTHESIS

The diagnostic performance of two qualitative, whole blood assays for measurement of myoglobin/creatine kinase (CK)-MB mass (CARDIAC STATus) and cardiac troponin T (TropT) was compared. Their potential in optimizing the rule-in of patients with infarction in order to initiate revascularization therapies was also evaluated.

METHODS

A group of 101 patients admitted to the hospital within 12 h from onset of symptoms suggestive of myocardial infarction was studied. A first blood sample was drawn in all patients immediately after admission. In patients not receiving reperfusion therapy (n = 61), three additional samples were also obtained 2, 4, and 6 h later.

RESULTS

CARDIAC STATus showed good performance in patients with an admission time > 2 h from onset of pain (diagnostic efficiency, 71-100%). Conversely, TropT was not sensitive enough for acceptable efficiency. In a subset of 39 patients admitted within 6 h who did not meet standard enrollment criteria for thrombolysis, CARDIAC STATus allowed early detection of almost 50% of infarcts, enabling a significant implementation of alternative revascularization therapies.

CONCLUSIONS

In patients admitted to the coronary care unit on the basis of case history and clinical examination, CARDIAC STATus assay is more effective than TropT in the early diagnosis of infarction, providing a valuable aid to cardiologists for confirming a suspected infarction rapidly, thus allowing, if indicated, recourse to revascularization therapy in clinically uncertain cases.

Cardiac troponins

Cardiac troponins I and T are proteins integral to the function of cardiac muscle. They are very sensitive markers for the detection of myocardial damage, and the ability to assay their serum levels accurately and quickly have revolutionized the concepts of minor myocardial injury and infarction. They are also powerful prognostic indicators of future adverse cardiac events. Limitations, more of troponin T than I, include decreased specificity in renal failure and skeletal muscle disease. Rapid, whole blood assays are now available that can be done at the patient's bedside. This review discusses the cardiac troponins, their biochemistry, the assays for them currently available, and their roles in the evaluation of cardiac disease in the Emergency Department (ED).

Measurement of cardiac troponins

The cardiac troponins form part of the regulatory mechanism for muscle contraction. Specific cardiac isoforms of cardiac troponin T and cardiac troponin I exist and commercially available immunoassay systems have been developed for their measurement. A large number of clinical and analytical studies have been performed and the measurement of cardiac troponins is now considered the 'gold standard' biochemical test for diagnosis of myocardial damage. There have been advances in understanding the development and structure of troponins and their degradation following myocardial cell necrosis. This has contributed to the understanding of the problems with current assays. Greater clinical use has also highlighted areas of analytical and clinical confusion. The assays are reviewed based on manufacturers' information, current published material as well as the authors' in-house experience.

Long-term prognostic value of serial troponin T bedside tests in patients with acute coronary syndromes

The early presence of troponin T in serum strongly predicts short-term mortality and myocardial infarction in patients with acute coronary syndromes. We investigated the long-term outcome of the prognostic significance of the troponin T rapid bedside assay (TROPT) and compared this with the quantitative troponin T assay (cTnT enzyme-linked immunosorbent assay), myoglobin and creatine kinase-MB (CK-MB) mass. One hundred sixty-three patients with chest pain and suspected acute coronary syndromes were studied and followed prospectively for 3 years. Serial blood specimens were obtained at admission and at 3, 6, 12, 24, 48, 72, and 96 hours after admission. Patients were classified as having acute myocardial infarction in 99 patients (61%), unstable angina in 34 patients (21%), and no evidence for acute cardiac ischemia in 30 patients (18%). At 3 years, 28 patients (17%) had died of which 25 deaths (15%) were for cardiac reasons. Twenty-one patients (13%) had a nonfatal (recurrent) myocardial infarction. At admission 29% of the patients were TROPT positive (> or = 0.2 microg/L), another 31% became positive within 12 hours, and 39% remained negative. When adjusted for baseline variables, a positive TROPT (any sample 0 to 12 hours) was independently associated with a higher risk of cardiac mortality (RR 4.3, 95% confidence interval [CI] 1.3 to 14.0). Because troponin T stays elevated up to 2 weeks, later TROPT results between 24 and 96 hours remained significantly predictive for mortality. The cTnT enzyme-linked immunosorbent assay (any sample 0 to 12 hours; cutoff > or = 0.2 microg/L) was similarly predictive (RR 2.9, 95% CI 1.0 to 8.6). Early myoglobin results were significantly prognostic for cardiac mortality up to 12 hours after admission (RR 3.7; 95% CI 1.0 to 12.0). In contrast, serial CK-MB mass measurements were not predictive of mortality. Thus, a combination of a baseline TROPT and an additional TROPT 12 hours or later identifies a subgroup of patients at high risk for subsequent mortality and reinfarction, both at short-term but also at long-term.

Evaluation of a point-of-care system for quantitative determination of troponin T and myoglobin

We present the results of a multicenter evaluation of a new point-of-care system (Cardiac Reader) for the quantitative determination of cardiac troponin T (CARDIAC T Quantitative test) and myoglobin (CARDIAC M test) in whole blood samples. The Cardiac Reader is a CCD camera that optically reads the immunochemical test strips. The measuring range is 0.1 to 3 microg/l for CARDIAC T Quantitative and 30 to 700 microg/l for CARDIAC M. Both tests are calibrated by the manufacturer. The reaction times of the tests are 12 or 8 minutes, respectively. Method comparisons were performed with 281 heparinized blood samples from patients with suspected acute coronary syndromes. The results obtained with CARDIAC T Quantitative showed a good agreement compared with cardiac troponin T ELISA (r = 0.89; y = 0.93x + 0.02). The method comparison between CARDIAC M and Tina-quant Myoglobin also showed a good agreement between both assays (r = 0.98; y = 0.92x + 1.6). Test lot-to-lot comparisons yielded differences of 2% and 6% for CARDIAC T Quantitative and of 0 to 11% for CARDIAC M. The within-run imprecision with blood samples and control materials was acceptable for CARDIAC T Quantitative (CV 10 to 15%) and good for CARDIAC M (CV 5 to 10%). The between-instrument CV was below 7% for CARDIACT Quantitative and below 5% for CARDIAC M. The cross-reactivity of CARDIAC T Quantitative with skeletal troponin T was approximately 0.003%. No significant analytical interference was detected for any of the assays in investigations with biotin (up to 100 microg/l), hemoglobin (up to 0.125 mmol/l), hematocrit (26 to 52%), bilirubin (up to 340 micromol/l), triglycerides (up to 5.0 mmol/l), and 18 standard drugs. With the Cardiac Reader reliable quantitative results can be easily obtained for both cardiac markers. The system is, therefore, particularly suitable for use in emergency rooms, coronary care units and small hospitals.

Analytical and clinical performance of an improved qualitative troponin T rapid test in laboratories and critical care units

OBJECTIVE

To evaluate the performance of a visual troponin T rapid test in the hands of nontraditionally trained personnel of 2 critical care units in comparison to 3 laboratories.

METHODS

Method comparisons of the troponin T rapid test versus cardiac troponin T enzyme-linked immunosorbent assay were performed with 804 samples from 510 patients with suspected acute coronary syndromes. Cross-reactivity with skeletal troponin T was studied up to 5000 microg/L.

RESULTS

Laboratories and critical care units obtained comparable results in the analytical cutoff of the test (0.11 and 0. 10 microg/L) and in the diagnostic sensitivities in the detection of acute myocardial infarction (96% and 93% after 8 hours) and of high-risk patients with unstable angina pectoris (100% and 100%). Different percentages of false-positive results (0.2% and 3%) were found, which may reflect different objectives and strategies in these hospital units. The cross-reactivity with skeletal troponin T was less than 0.01%.

CONCLUSIONS

The troponin T rapid test gives reliable results not only when used by laboratory personnel experienced in the execution of analytical methods, but also in the hands of nurses and physicians working in clinical units outside the laboratory.

Laboratory diagnosis of patients with acute chest pain

The enzyme activities of creatine kinase (CK), its isoenzyme MB (CK-MB) and of lactate dehydrogenase isoenzyme 1 (LD-1) have been used for years in diagnosing patients with chest pain in order to differentiate patients with acute myocardial infarction (AMI) from non-AMI patients. These methods are easy to perform as automated analyses, but they are not specific for cardiac muscle damage. During the early 90's the situation changed. First creatine kinase MB mass (CK-MB mass) replaced the measurement of CK-MB activity. Subsequently cardiac-specific proteins troponin T (cTnT) and troponin I (cTnI) appeared on the scene, displacing LD-1 analysis. However, troponin concentrations in blood increase only from four to six hours after onset of chest pain. Therefore a rapid marker such as myoglobin, fatty acid binding protein or glycogen phosphorylase BB could be used in early diagnosis of AMI. On the other hand, CK-MB isoforms alone may also be useful in rapid diagnosis of cardiac muscle damage. Myoglobin, CK-MB mass, cTnT and cTnI are nowadays widely used in diagnosing patients with acute chest pain. Myoglobin is not cardiac-specific and therefore requires supplementation with some other analyses such as troponins to support the myoglobin value. Troponins are very highly cardiac-specific. Only the sera of some patients with severe renal failure, which requires hemodialysis, have elevated cTnT and/or cTnI without there being any evidence of cardiac damage. On the other hand, the latest studies have shown that elevated troponin levels in sera of hemodialysis patients point to an increased risk of future cardiac events in a similar manner to the elevated troponin values in sera of patients with unstable angina pectoris. In addition, the bedside tests for cTnT and cTnI alone or together with myoglobin and CK-MB mass can be used instead of quantitative analyses in the diagnosis of patients with chest pain. These rapid tests are easy to perform and they do not require expensive instrumentation. For routine clinical laboratory practice we suggest that in diagnosis of patients with chest pain, myoglobin and CK-MB mass measurements should be performed whenever they are requested (24 h/day) and cTnT or cTnI on admission to the hospital and then 4-6 and 12 hours later.

Myoglobin, creatine kinase MB, troponin T, and troponin I - rapid bedside assays in patients with acute chest pain

Three new rapid, qualitative bedside immunoassays were evaluated in the diagnosis of patients with acute chest pain. The subjects, 122 patients in group 1 (bedside tests for myoglobin, creatine kinase MB) and 233 patients in group 2 (bedside tests for troponin I and sensitive troponin T) were admitted to hospital with acute chest pain for less than 12 h. The bedside tests were performed on admission, and 2, 4, and 6 h later. The correlation between the two parts of the rapid creatine kinase MB/myoglobin test during the first 12 h after the onset of chest pain was moderate in all patients (kappa=0.401, 95% confidence interval 0.321-0.483). The highest correlation was seen with the patients with definite and probable myocardial infarction. The correlations were smaller but significant also in other diagnostic groups (unstable angina pectoris, prolonged chest pain, and non-cardiac chest pain). The correlation between the rapid sensitive test for troponin T and rapid test for troponin I was significant in all groups (kappa=0.776, 95% confidence interval 0.711-0.841). The myoglobin part of the rapid creatine kinase MB/myoglobin test may be too non-specific for clinical diagnostic purposes [in non-infarct patients the myoglobin part was significantly more often positive than creatine kinase MB or troponin tests (P<0.001)].

Quantitative Bedside Assay for Cardiac Troponin T: A Complementary Method to Centralized Laboratory Testing

Background: In the evaluation of chest pain patients, whole blood bedside assays of highly specific cardiac molecules may be an attractive alternative to centralized clinical chemistry testing. We now report on an optimized test strip device for cardiac troponin T (cTnT) that can be analyzed by a cardiac reader for quantitative assessment of the test result.

Methods and Results: The cTnT test strip reader measures, via a CCD camera, the reflectance of the signal line. For quantitative analysis, a calibration curve was constructed from 1030 samples of 252 consecutive patients with acute coronary syndromes. In a method comparison of 140 samples, the quantitative results of the cTnT test strip reader correlated closely with the results of the cTnT ELISA (r = 0.98; y = 0.85x + 0.002). Within-run and day-to-day (n = 10) mean CVs were between 11% and 16%, respectively. The cross-reactivity with skeletal troponin T was &lt;0.02%. In patients with myocardial infarction, 45% and 91% of all samples were positive on admission and at 4–8 h after the onset of symptoms, respectively. ROC curve analysis demonstrated a comparable efficiency of the cTnT test strip reader and the laboratory-based cTnT ELISA in patients with suspected myocardial infarction.

Conclusions: It is now possible to quantitatively determine cTnT at the patient’s bedside with a rapid and convenient test device. This will facilitate the diagnostic work up of patients with suspected myocardial cell necrosis.

Multisite study of a second generation whole blood rapid assay for cardiac troponin T

We evaluated a second generation, qualitative, whole blood rapid assay for cardiac troponin T (cTnT), which employs a more cardio-specific troponin T mouse monoclonal capture antibody. Using quantitative cTnT enzyme-linked immunosorbent assay (ELISA) results as the benchmark for accuracy, we compared the performance of the second generation and the original whole blood rapid assays in 445 samples from patients with the following diagnoses, determined by medical record review: myocardial infarction, coronary bypass surgery, ischaemic heart disease, musculoskeletal disease, renal failure or other noncardiac conditions. Overall, concordance between the second generation cTnT Rapid Assay and the quantitative cTnT ELISA, compared using the McNemar test and a cut-off concentration of 0.1 microgram/L, was in the range 76-94% for each patient group. Using a receiver operating characteristic plot, the cut-off for the second generation cTnT Rapid Assay was in the range 0.06-0.08 microgram/L. We conclude that the second generation cTnT whole blood assay has a 2.5-fold lower analytical cut-off than the original rapid assay (0.2 microgram/L) and may represent a more sensitive clinical tool for the rapid triage and risk stratification of cardiac patients.

Cardiac markers: point of care testing

Point-of-care (POC) or "near-patient" testing allows diagnostic assays to be performed in locations such as the emergency department or intensive care unit where treatment decisions are made and care is delivered based on the results of these assays. Presently, there exist POC immunoassays for several cardiac markers including creatine kinase MB (CK-MB), myoglobin, troponin I, and troponin T that yield qualitative and quantitative results comparable to traditional central lab assays. In the evaluation of emergency room patients with chest pain, POC cardiac markers may improve triage and clinical outcomes. Existing POC assays combining myoglobin and CK-MB have high sensitivity and specificity for diagnosing acute myocardial infarction and may provide the earliest identification of myocardial injury. POC Troponin T assays are the most studied POC cardiac marker assays. Along with POC troponin I assays, these tests provide more sensitive identification of myocardial injury and valuable prognostic information. Prior studies of POC cardiac marker assays have not addressed whether POC testing affects patient outcome or process of care. In situations in which caregivers base triage, treatment and monitoring decisions on time-sensitive diagnostic results, POC tests linked with improved triage and treatment strategies may improve resource utilization and clinical outcomes.

Use of biochemical markers in acute coronary syndromes. IFCC Scientific Division, Committee on Standardization of Markers of Cardiac Damage. International Federation of Clinical Chemistry

This paper presents evidence and suggestions from the IFCC Committee on "Standardization of Markers of Cardiac Damage" (C-SMCD) on the use of biochemical markers for the triage diagnosis of acute coronary syndromes. There is general agreement that both 'early' and 'definitive' biochemical markers of myocardial damage are necessary and that these assays must be available with a turnaround time of 1 h or less. Currently, myoglobin is the marker that most effectively fits the role as an 'early' marker, whereas 'definitive' markers are cardiac troponins. Since the sensitivity of the initial electrocardiogram is only 50% for detecting myocardial infarction, the use of biochemical markers may significantly contribute to the early diagnosis and become relevant when the electrocardiogram is not diagnostic. In addition, new sensitive biochemical markers, particularly the cardiac troponins, are presently the best to detect the presence of minor myocardial cell damage. With regard to this, two decision limits are probably needed for the optimal use of troponins: a low abnormal value suggesting the presence of myocardial damage and a higher value suggesting the diagnosis of myocardial infarction according to traditionally used criteria. Properly designed studies should be performed to establish limits for each commercially available troponin assay. Finally, it is recognized that there is no need for the use of any biochemical marker when the clinical diagnosis is unequivocal, other than for diagnosing reinfarction, estimating the infarct size, and monitoring thrombolytic therapy.

IFCC Committee on Standardization of Markers of Cardiac Damage: premises and project presentation. International Federation of Clinical Chemistry and Laboratory Medicine

The field of biochemical markers of cardiac damage is in a dynamic state, with new applications continually appearing and new assays and markers being developed. These significant and sudden advancements in the development of new biochemical assays have led however to several analytical and interpretative problems. In this situation, it is essential that a uniform and rigorous outlook be maintained to ensure optimal test utilization. For these reasons, the IFCC Scientific Division recently agreed to establish a Committee on "Standardization of Markers of Cardiac Damage" (C-SMCD), inviting members from the established American and European groups to become members of this Committee. In this presentation, the premises, the issues, and the proposed plan of action of C-SMCD are presented and discussed.

Troponin T: a sensitive and specific diagnostic and prognostic marker of myocardial damage

Cardiac troponin T (cTnT) in serum is a highly sensitive and specific marker for myocardial damage. Quantitative immunoassays take 9 min. A rapid test (TropT, CardiacT) using plasma detects cTnT concentrations above 0.10 microg/l within 15 min. Both assays are specific for the cardiac isoform. In a study using the maximal values from serial sampling in 502 infarction-suspected patients, we found a diagnostic sensitivity for non-Q- and Q-wave infarctions of 100%, with a specificity of 99%. cTnT has been shown to be a powerful prognostic marker for risk stratification in acute coronary syndromes. In 30-40% of patients with unstable angina, cTnT > or = 0.10 microg/l detects minor myocardial damage (MMD) with poor prognosis. False positives may be found in certain skeletal muscle diseases, such as polymyositis and Duchenne's muscular dystrophy. Constantly increased values in renal failure may be due to uremic cardiomyositis. Even in uremia, a rapid increase of cTnT will indicate acute myocardial damage. We propose a diagnostic strategy based on timed, parallel determinations of myoglobin + cTnT.

Excellent reliability of nurse-based bedside diagnosis of acute myocardial infarction by rapid dry-strip creatine kinase MB, myoglobin, and troponin T

With the aim to compare the diagnostic efficacy as regards acute myocardial infarction of two rapid dry-strip tests, one with both creatine kinase MB (CK-MB) and myoglobin (C + M) and the other with troponin T, and to test the reliability of bedside diagnosis by the coronary care unit (CCU) nurse, 151 patients with acute chest pain admitted to the CCU were investigated. There was no difference in diagnostic performance between rapid tests and quantitative determinations. With <6-hour duration of symptoms, the sensitivity was better for C + M than for troponin T (72% vs 33%, p < 0.05). With symptoms lasting >12 hours on arrival, troponin T performed better, with 100% sensitivity and a negative predictive value of 100% in the 6-hour retest. For exclusion of damage, the two tests have similar and reliable diagnostic capacities 12 hours after the onset of symptoms. The bedside diagnosis or exclusion of acute myocardial infarction was carried out rapidly (within 20 minutes) and reliably by the CCU nurses.