The Alpha Dx POINT-OF-NEED System

Introduction Cardiac markers are vital to making clinical management decisions in patients presenting with chest pain. Because they can reduce the turnaround time for this critical information, there is growing interest in the use of point-of-care (POC) systems in decentralized settings such as the emergency department. However, if the quality of results is not equivalent to the results produced by the laboratory, the utility of these systems is compromised. The National Association of Clinical Biochemistry (NACB) has provided specific recommendations for the use of cardiac markers in diagnosing coronary artery disease. The current study evaluates how well the Alpha Dx POINT-OF-NEED System (First Medical, Mountain View, CA) meets these guidelines. Specifically, assay precision at the clinical cutoffs for each assay was evaluated across three test disc lots of consumables and found to meet or exceed the requirement of assay coefficient of variation (CV) of < 10%. For cardiac troponin I, the precision near the clinical cutoff (0.4 μg/L) ranged from 7.5% to 8.9%. CVs obtained for the other analytes around the clinical cutoffs ranged from 3.2% to 7.0%. Rapid, whole blood POC systems for quantitative cardiac marker testing can improve patient management by reducing the turnaround time for critical clinical information. Not only must these systems be appropriate for use in decentralized testing settings, but they must also meet the same analytical requirements of larger, central laboratory analyzers. The NACB has published recommendations for the use of cardiac markers in coronary artery disease,1 which include the following requirements: serial testing over 6 to 9 hours after admission, the use of multiple markers, marker data referenced to symptom onset and time of presentation, a routine turnaround time of less than 1 hour (or POC testing), the use of whole blood (or plasma) samples to speed turnaround time, clinical cutoffs defined by receiver-operator curve (ROC) analysis, and assay CV of less than 10% at the critical clinical decision point. The Alpha Dx POINT-OF-NEED System The Alpha Dx POINT-OF-NEED System consists of a small tabletop analyzer and a single use device, the test disc that contains all of the dried reagents necessary to run a cardiac marker profile.2 Up to four analytes may be tested simultaneously: myoglobin, total creatine kinase (CK) mass, CK-MB mass, and cardiac troponin I (cTnI). The test disc also contains bilevel controls for each analyte, for a total of up to eight control results with every patient sample. The assay technology is solid-phase sandwich immunoassay with fluorescence detection. Each lot of test discs is precalibrated. A lot-specific calibration diskette that contains calibration information, expiration dating, and quality control limits is inserted into the analyzer once per lot. Calibration information for up to 300 lots may be maintained on the analyzer. The patient sample is introduced into the analyzer and onto the test disc using a whole blood, closed primary tube sampling device (Safe-T-Coupler Unit, First Medical, Mountain View, CA). Reagents on the test disc are rehydrated with fluid from the onboard fluid cassette. Magnetically-activated stainless steel balls within the reagent chambers facilitate mixing, and fluid is transferred within the test disc by spinning the test disc. Printed results are available in less than 18 minutes. The onboard test disc bilevel controls will automatically suppress a patient result if the control values fall outside predefined ranges. The system software offers institution definable options for displaying data in various formats. Results that are above the institution defined clinical cutoff are flagged. The upper reference limit and clinical cutoff for each marker are printed with the patient results. Serial sample results, referenced to symptom onset, time from first sample, or both, can be monitored graphically for easier interpretation (Fig. 1). Additional patient demographic information may be entered into the analyzer software and the data for up to 50,000 patient samples is maintained and can be easily retrieved from memory.Fig 1: Patient profile display from the Alpha Dx.The purpose of this study was to validate that the Alpha Dx POINT-OF-NEED System meets the NACB recommendation for assay precision of less than 10% CV at the clinical cutoff for each of the four cardiac markers. Methods Three lots of test discs were tested. Whole blood was drawn into evacuated blood collection tubes (EDTA) from three different donors 1 to 3 days prior to the individual lot study. Approximately 45 to 55 mL was obtained from each donor. Since the three test disc lots were tested at different times, unique sample preparations were used for each test disc lot. Concentrated antigen solutions (myoglobin and CK-MM, Fortron, Morrisville, NC; cardiac troponin I, Bio Design, Saco, ME; CK-MB, Seradyn, Indianapolis, IN) were diluted in low, medium, and high concentrations using a buffer that contains various salts, detergents, and proteins to preserve and stabilize the antigens. Aliquots of these low, medium, and high antigen concentrations were added to 40 mL of whole blood. The sample was mixed gently for 3 to 6 minutes after addition of the antigen solutions and refrigerated at 2 to 8°C for at least 12 hours. The samples were then brought to room temperature for approximately 30 minutes and gently mixed for no more than 10 minutes. Samples were stored on ice while transferring to polypropylene tubes in 1.5 mL aliquots. A total of 24 test discs were tested for each lot. Lots A and B were tested across six analyzers and Lot C using four analyzers. Data were collected within a 4-hour time window to minimize the influence of potential analyte degradation. Results The Alpha Dx POINT-OF-NEED System ROC derived clinical cutoffs for each of the analytes are shown in Table 1.3 As shown in Table 2, the CVs for each analyte of the three lots of test discs tested were < 10%. For cardiac troponin I, the CVs near the clinical cutoff (0.4 μg/L) ranged from 7.5 to 8.9%. The CVs for the other analytes around the clinical cutoffs ranged from 3.2 to 7.0%.Table 1: Alpha Dx POINT-OF-NEED system clinical cutoff valuesTable 2: Whole blood precision for multiple lots of alpha Dx test discsDiscussion Rapid testing of multiple cardiac markers has been shown to detect patients who are at greater risk for adverse outcomes earlier4 and to more economically rule-out patients who do not have significant coronary events.5 These studies are encouraging the move toward POC testing using newer technologies. In addition to meeting the analytical requirements of the NACB for cardiac marker testing, POC systems must also be easy enough to operate and have the reliability necessary for use in decentralized testing. With no sample preparation, bar-coded sample capability, no calibration, automatic quality control with each sample, and direct Laboratory Information System (LIS) connectivity, the Alpha Dx POINT-OF-NEED System was designed to meet these needs. The System was evaluated in a clinical trial with operation in various clinical settings (one emergency department, two coronary care units, and one laboratory) and found to be appropriate for use in decentralized testing.3 Finally, all testing, including decentralized testing, is regulated by The Clinical Laboratory Improvements Amendments of 1988 (CLIA 1988) to ensure the quality of the testing, regardless of the testing site.6 The Alpha Dx POINT-OF-NEED System includes features to facilitate compliance including operator lockout capability, a training log, reagent usage tracking, automatic quality control, and quality control monitoring tools such as Levey-Jennings charts and statistics calculations. In addition to the onboard bilevel controls with each patient sample, the system includes a comprehensive quality monitoring system to ensure that operator errors (such as attempting to insert an expired test disc) are detected and testing stopped until the error is corrected. The quality monitoring system operates continuously throughout the test process and checks for any potential electromechanical, optical, chemical, or data processing faults. Software algorithms verify the critical aspects associated with sample processing. The quality system has been validated and found to be an excellent example of how quality systems for POC analyzers should be designed.7 Conclusion In addition to meeting the NACB recommendations for multiple markers, whole blood testing, rapid turnaround time, referencing patient results to symptom onset or presentation time, and ROC curve derived clinical decision limits, the Alpha Dx POINTOF-NEED System meets the analytical requirement of CVs of less than 10% at the clinical cutoffs for each marker. The system has been independently evaluated and found to meet the clinical requirements for decentralized testing and to provide an excellent system for assurance of the quality of test results.3