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The Triage Cardiac Panel: Cardiac Markers for the Triage System

Clark, Thomas J. BS, MT (ASCP); McPherson, Paul H. PhD; Buechler, Kenneth F. PhD

Section Editor(s): Wu, Alan H. B. PhD

Cardiac Markers

Symposium Editor

Thomas J. Clark, Paul H. McPherson, and Kenneth F. Buechler are at Biosite Incorporated, San Diego, California.

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Introduction

The proper management of patients with chest pain remains a significant clinical and administrative challenge for hospitals throughout the United States. The availability of improved therapeutic interventions for acute myocardial infarction (AMI) and other acute coronary syndromes (ACS) makes rapid diagnosis and disposition of patients with these conditions essential. It is equally important to provide safe and rapid ruleout for low-risk patients. Investigators have evaluated new clinical algorithms and critical pathways to rapidly diagnose and triage patients with chest pain in the emergency department. A key component of these new strategies involves the use of a panel of biochemical cardiac markers, rather than a single marker, and measuring their levels in multiple blood samples drawn serially after onset of symptoms as part of an accelerated diagnostic protocol. New consensus guidelines recognize the importance of adopting an accelerated care pathway for chest pain diagnosis and the benefits of serially measuring a panel of cardiac markers during the early triage period.

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The Triage System

The Triage System (Biosite Incorporated, San Diego, CA) is a point-of-care (POC) system that reduces complex immunoassay procedures to rapid and portable self-performing tests. The Triage System is comprised of a portable instrument, the Triage MeterPlus, and a disposable protein chip or assay device, such as the Triage Cardiac Panel. The assay is performed using a sample comprised of whole blood or plasma. The test procedure involves the addition of several drops of sample to the device, insertion of the device into the meter, and reading the results from the display screen or automatic printout. The results for all analytes are quantified simultaneously within approximately 15 minutes after addition of the sample to the device.

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Assay Principle

The Triage Cardiac Panel is a fluorescence immunoassay for the quantitative determination of the cardiac proteins creatine-kinase-MB (CK-MB), myoglobin, and troponin I (cTnI) in whole blood and plasma specimens using heparin as the anticoagulant. The test is used as an aid in the diagnosis of myocardial infarction. Novel concepts of capillarity move fluids within microcapillaries in the device. After addition of a blood sample to the sample port, the red cells are separated from the plasma via a filter contained in the device. The plasma sample enters a reaction chamber in which fluorescent antibody conjugates are deposited. The cardiac proteins in the plasma react with the fluorescent antibody conjugates within the reaction chamber. After sufficient incubation has occurred, the reaction mixture flows through a protein array containing discrete zones of antibodies that are immobilized on the surface of the microcapillary. The antibody in each zone is specific for one of the cardiac proteins. Complexes of the cardiac proteins and fluorescent antibody conjugates are captured by the antibodies in the discrete zones on the protein array. The concentration of each cardiac protein in the specimen is proportional to the fluorescence from the zone for that protein detected by the meter (Fig. 1).

Fig 1

Fig 1

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The Triage MeterPlus

The Triage MeterPlus is a portable, battery-powered fluorometer. It measures the fluorescence from the discrete zones on the protein array. The fluorescent dyes utilize fluorescence energy transfer to yield novel excitation and emission wavelengths.1 The excitation wavelength of the donor dye (670 nm) coincides with the output of the laser diode in the meter. The detector is a silicon photodiode that measures the emission light (760 nm) of the acceptor dye with a quantum efficiency of approximately 85%. A motor in the meter drives the device under the optic block for the measurement of fluorescence at the discrete assay zones. The fluorescence measurement is converted into an electrical signal that is then transformed into an analyte concentration using lotspecific calibration curves stored in the meter memory. The calibration curves and other lot-specific information such as the expiration date of the device are downloaded into the meter memory from a small code chip that is programmed at Biosite and supplied with each kit of devices. The meter reads a barcode printed on each device to identify the lot. The assay results are displayed on a liquid crystal display (LCD) and can be printed by the built-in printer and uploaded automatically to a hospital information system.

The Triage MeterPlus is simple to operate and uses an intuitive user interface. The LCD screen prompts the user through the menu options, which are selected using the numeric keypad. Software lockouts allow only trained personnel to use the system and only after the periodic quality control requirements have been met. A special supervisor code chip must be used in order to change testing parameters such as frequency of calibration verification checks, cut off concentrations and user identification, or before deleting patient results (Fig. 2).

Fig 2

Fig 2

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Product Features

Selection of a POC testing system goes beyond the need to provide rapid, accurate, and reliable results. A comprehensive assessment of the needs of the institution will allow the operator to choose a system that will ensure the best possible patient care in a costeffective manner. Testing should meet rigorous quality standards and regulatory requirements, yet it must create minimal demand on resources and staff in the testing environment. The Triage System has been designed with these important POC considerations. A description follows of some of the important product features and potential benefits to the POC user.

Results for all three cardiac markers on the Triage Cardiac Panel are available simultaneously within approximately 15 minutes after addition of the sample to the device. This short turnaround time allows rapid serial testing at the point of care. Serial testing that includes early and definitive markers for myocardial necrosis (such as myoglobin, CK-MB, and cTnI) allows for rapid identification or exclusion of AMI regardless of the time of patient presentation to the ED after the onset of chest pain. Detection of increasing marker values, even within the normal range of the assay, may raise the suspicion for ACS.

Since various forms of cTnI are released from damaged heart cells into the blood, and change into different forms in the blood, cTnI antibodies must recognize each form with approximate equal affinity. The Triage Cardiac Panel troponin I assay measures the oxidized and reduced forms of free troponin I, troponin I/C, troponin I/T, and troponin I/C/T. Each form is measured to approximately the same extent, and ensures that the reported value is independent of the form of cTnI in the sample.

The Triage Cardiac Panel allows the use of whole blood samples. The filter in the device separates blood cells from plasma, eliminating delays in testing due to sample processing.

An automatic endpoint detection technology allows devices to be run independent of the meter, enabling efficient throughput of up to 30 devices (90 marker results) per hour per meter. Internal assay controls on the device, and electronic controls in the meter, combined with software lockout features ensure high quality results without excess demand on users. In the event of failure of any of the quality control tests, the system displays the test that failed and locks the user out from further testing until the failure is resolved.

Calibration curves for each lot of devices are determined at Biosite and are downloaded into the Triage MeterPlus from a lot-specific code chip supplied with each kit. The calibration curves are accurate for the entire shelf life of the device, so the user never needs to perform calibration. The expiration date of the device is also downloaded to the meter memory from the code chip. A bar code on the device is read by the meter to identify the lot and allow the meter software to select the correct calibration and expiration data stored in the meter memory. A fluorescent internal standard is also measured by the meter prior to each measurement to assure proper laser calibration and electronic function.

The Triage MeterPlus has a small footprint and the use of an AC/DC adapter or four AA batteries provide the portability needed for POC applications.

Results are automatically displayed on a LCD and can be set to print out automatically from the built-in printer. A result that falls outside the normal range is displayed in reverse video for easy viewing. Results are processed automatically by the meter after insertion of the device. Patient results and quality control data are stored in the meter memory and can be recalled by following the LCD screen prompts and using the numeric keypad. The Triage Census Plus data management software enables full connectivity of the Triage System to a laboratory information system (LIS). Results can be automatically uploaded to a LIS for proper ordering, reporting, billing, and tracking of testing.

The Triage MeterPlus has an expanded test menu that includes the Triage Cardiac Panel, the Triage BNP Test, and the Triage Tox Drug Screen. The Triage BNP test measures B-Type Natriuretic Peptide (BNP) as an aid in the diagnosis of congestive heart failure. The Triage Tox Drug Screen is a qualitative urine test that detects the presence of nine commonly-abused drugs. In addition, Biosite is developing rapid tests for stroke, ACS, and sepsis to be run on the same meter.

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Clinical Performance

Apple et al. first reported on a multi-center study that assessed the performance of the Triage Cardiac Panel as an aid in the diagnosis of myocardial infarction.2 Optimum cutoffs for the discrimination of AMI as determined by ROC curve analysis were set at 0.4 ng/mL for cTnI, 4.3 ng/mL for CK-MB, and 107 ng/mL for myoglobin. The Triage Cardiac Panel demonstrated comparable sensitivities and specificities for the diagnosis of AMI in patients presenting with chest pain versus cTnI, CK-MB, and myoglobin assays run on three separate laboratory analyzers. The sensitivity and specificity, respectively, for each marker was: cTnI, 98% and 100%; CK-MB, 95% and 91%; and myoglobin, 81% and 92%. The authors concluded that the Triage Cardiac Panel was comparable to established laboratory assays and offered clinicians a whole blood POC analysis of multiple cardiac markers that provides excellent clinical sensitivity and specificity for the detection of AMI.

Recently, several studies have been published that document the clinical performance of the Triage Cardiac Panel and its ability to support accelerated care pathways for patients with chest pain in the emergency room setting. Ng et al. looked at 1,285 consecutive patients with signs and symptoms of cardiac ischemia.3 By utilizing serial bedside cardiac marker testing with cTnI, a change in myoglobin, and CK-MB measurements over 90 minutes, they reported a sensitivity of 100% and specificity of 96% for myocardial infarction within 90 minutes of patient presentation. As a result, critical care unit admissions decreased by 40%. Ninety percent of patients with negative cardiac markers and a negative electrocardiogram (ECG) at 90 minutes were discharged, with 1 patient returning with myocardial infarction (0.2%) within 30 days. The study concluded that a simple, inexpensive, yet aggressive critical pathway that utilizes high-risk features from clinical history, electrocardiogram changes, and rapid POC testing of three cardiac markers allows for accurate triaging of chest pain patients within 90 minutes of presenting to the emergency department.

McCord et al evaluated a similar strategy for the rapid rule-out of myocardial infarction using a 90-minute diagnostic algorithm.4 The study enrolled 817 consecutive patients in the emergency department who were evaluated for possible myocardial infarction. In patients with nondiagnostic electrocardiograms, cTnI, CK-MB, and myoglobin were measured with the Triage Cardiac Panel at presentation and at 90 minutes, 3 hours, and 9 hours. Standard central laboratory testing of CK-MB was done at the same time intervals, and triage decisions were made by emergency department physicians who were unaware of the POC results. Sensitivity and negative predictive value were compared for the multiple-marker, POC approach and the central laboratory strategy. Sensitivity and negative predictive value for the combination of myoglobin and cTnI by 90 minutes was 96.9% and 99.6%, respectively. In combination with myoglobin and cTnI, CK-MB measurements and blood sampling at 3 hours did not improve the sensitivity or negative predictive value of myoglobin and cTnI together. Median time from sampling to reporting of results was 71 minutes for the central laboratory versus 24 minutes for the Triage Cardiac Panel (P < 0.001). The study concluded that AMI can be excluded rapidly in the emergency department by use of POC measurements of myoglobin and cTnI during the first 90 minutes after presentation.

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Conclusions

The diagnosis and risk stratification of patients suspected of suffering from ACS remains a difficult task. The process of managing ACS patients in the emergency department needs to be rapid, accurate, and cost-effective. The use of new care pathways and critical algorithms that incorporate rapid, multimarker strategies have demonstrated promise in guiding appropriate diagnosis, disposition, and therapy. In order to provide cardiac marker results in a time frame capable of supporting these accelerated protocols, assays like the Triage Cardiac Panel are being evaluated for their application in the emergency department. The POC systems should be implemented as an extension of the clinical laboratory and under its control. It is also essential that the systems be evaluated not only for their ability to provide accurate, reliable results, but also on their ability to meet the needs of the emergency department. Improved patient outcomes and workflow efficiencies will only be achieved if physician practice is altered. The Triage Cardiac Panel and the Triage System offer an innovative solution to rapid cardiac marker testing and reporting of results.

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References

1. Buechler, KF. Near Patient Tests: Triage Cardiac System. In: Wild D, ed. The Immunoassay Handbook. New York, NY: Nature Publishing Group; 2001:385-389.
2. Apple FS, Christenson RH, Valdes R Jr, et al. Simultaneous rapid measurement of whole blood myoglobin, creatine kinase MB, and cardiac troponin I by the Triage Cardiac Panel for detection of myocardial infarction. Clin Chem 1999;45:199-205.
3. Ng SM, Krishnaswamy P, Morissey R, et al. Ninety-minute accelerated critical pathway for chest pain evaluation. Am J Cardiol 2001;88:611-617.
4. McCord J, Nowak RM, McCullough PA, et al. Ninety-minute exclusion of acute myocardial infarction by use of quantitative point-of-care testing of myoglobin and troponin I. Circulation 2001;104:1483-1488.
© 2002 Lippincott Williams & Wilkins, Inc.