Point-of-care testing of cardiac markers: results from an experience in an Emergency Department

Bedside evaluation of cardiac markers

Accurate and rapid diagnostic tests can help identify high-risk patients with ACS among those presenting to the emergency department with chest pain. Such tests can also differentiate low-risk patients with chest pain who are suitable for early emergency department discharge. In this article, Drs Amsterdam and Deedwania elucidate the varieties of ACS, their pathophysiology, and the methods used for diagnosis. The authors also explore the potential of point-of-care testing for cardiac injury markers in the timely and accurate identification of ACS.

Use of portable blood physiology point-of-care devices for basic and applied research on vertebrates: a review

Non-human vertebrate blood is commonly collected and assayed for a variety of applications, including veterinary diagnostics and physiological research. Small, often non-lethal samples enable the assessment and monitoring of the physiological state and health of the individual. Traditionally, studies that rely on blood physiology have focused on captive animals or, in studies conducted in remote settings, have required the preservation and transport of samples for later analysis. In either situation, large, laboratory-bound equipment and traditional assays and analytical protocols are required. The use of point-of-care (POC) devices to measure various secondary blood physiological parameters, such as metabolites, blood gases and ions, has become increasingly popular recently, due to immediate results and their portability, which allows the freedom to study organisms in the wild. Here, we review the current uses of POC devices and their applicability to basic and applied studies on a variety of non-domesticated species. We located 79 individual studies that focused on non-domesticated vertebrates, including validation and application of POC tools. Studies focused on a wide spectrum of taxa, including mammals, birds and herptiles, although the majority of studies focused on fish, and typical variables measured included blood glucose, lactate and pH. We found that calibrations for species-specific blood physiology values are necessary, because ranges can vary within and among taxa and are sometimes outside the measurable range of the devices. In addition, although POC devices are portable and robust, most require durable cases, they are seldom waterproof/water-resistant, and factors such as humidity and temperature can affect the performance of the device. Overall, most studies concluded that POC devices are suitable alternatives to traditional laboratory devices and eliminate the need for transport of samples; however, there is a need for greater emphasis on rigorous calibration and validation of these units and appreciation of their limitations.

Point-of-care testing: where is the evidence? A systematic survey

Point-of-care testing (POCT) has had rapid technological development and their use is widespread in clinical laboratories to assure reduction of turn-around-time and rapid patient management in some clinical settings where it is important to make quick decisions. Until now the papers published about the POCT have focused on the reliability of the technology used and their analytical accuracy. We aim to perform a systematic survey of the evidence of POCT efficacy focused on clinical outcomes, selecting POCT denoted special analytes characterized by possible high clinical impact. We searched in Medline and Embase. Two independent reviewers assessed the eligibility, extracted study details and assessed the methodological quality of studies. We analyzed 84 studies for five POCT instruments: neonatal bilirubin, procalcitonin, intra-operative parathyroid hormone, troponin and blood gas analysis. Studies were at high risk of bias. Most of the papers (50%) were studies of correlation between the results obtained by using POCT instruments and those obtained by using laboratory instruments. These data showed a satisfactory correlation between methods when similar analytical reactions were used. Only 13% of the studies evaluated the impact of POCT on clinical practice. POCT decreases the time elapsed for making decisions on patient management but the clinical outcomes have never been adequately evaluated. Our work shows that, although POCT has the potential to provide beneficial patient outcome, further studies may be required, especially for defining its real utility on clinical decision making.

Cardiac biomarkers in acute myocardial infarction

Each year, a large number of patients are seen in the Emergency Department with presentations necessitating investigation for possible acute myocardial infarction. Patients can be stratified by symptoms, risk factors and electrocardiogram results but cardiac biomarkers also have a prime role both diagnostically and prognostically. This review summarizes both the history of cardiac biomarkers as well as currently available (established and novel) assays. Cardiac troponin, our current "gold standard" biomarker criterion for the diagnosis of myocardial infarction has high sensitivity and specificity for this diagnosis and therapies instituted in patients with elevated troponin have been shown to influence outcomes. Other markers of myocardial necrosis, inflammation and neurohormonal activity have also been shown to have either diagnostic or prognostic utility, but none have been shown to be superior to troponin. The measurement of multiple biomarkers and the use of point of care markers may accelerate current diagnostic protocols for the assessment of such patients.

A novel chemiluminescence paper microfluidic biosensor based on enzymatic reaction for uric acid determination

In this work, chemiluminescence (CL) method was combined with microfluidic paper-based analytical device (μPAD) to establish a novel CL μPAD biosensor for the first time. This novel CL μPAD biosensor was based on enzyme reaction which produced H(2)O(2) while decomposing the substrate and the CL reaction between rhodanine derivative and generated H(2)O(2) in acid medium. Microchannels in μPAD were fabricated by cutting method. And the possible CL assay principle of this CL μPAD biosensor was explained. Rhodanine derivative system was used to reach the purpose of high sensitivity and well-defined signal for this CL μPAD biosensor. And the optimum reaction conditions were investigated. The quantitative determination of uric acid could be achieved by this CL μPAD biosensor with accurate and satisfactory result. And this biosensor could provide good reproducible results upon storage at 4°C for at least 10 weeks. The successful integration of μPAD and CL reaction made the final biosensor inexpensive, easy-to-use, low-volume, and portable for uric acid determination, which also greatly reduces the cost and increases the efficiency required for an analysis. We believe this simple, practical CL μPAD biosensor will be of interest for use in areas such as disease diagnosis.

Surface plasmon resonance aided electrochemical immunosensor for CK-MB determination in undiluted serum samples

This article presents a simple chronoamperometric immunosensor for the quantitative assessment of creatine kinase MB (CK-MB) in 50 microL undiluted serum samples. The immunosensor consists of gold working and counter electrodes patterned onto a glass chip by thin-film photolithography and an external Ag|AgCl reference electrode. The detection limit (DL) of the chronoamperometric method is 13 ng mL(-1) (DL = 2xRMSD/S, where RMSD is the residual mean standard deviation of the measured points around a calibration curve with a slope of S). In spiked serum samples, the response was linear up to 300 ng mL(-1) of CK-MB. A surface plasmon resonance (SPR) system with simultaneous electrochemical detection (EC-SPR) aided the development of the sandwich immunoassay. Real-time monitoring of the SPR signal was used to optimize the capture antibody immobilization, CK-MB and detection antibody binding, as well as to minimize the nonspecific adsorption of serum proteins to the sensor surface. The detection antibody has been labeled with alkaline phosphatase (ALP) enzyme for sensitive electrochemical detection. ALP catalyzes the hydrolysis of ascorbic acid phosphate and generates ascorbic acid, which is measured chronoamperometrically. The electrochemical immunoassay for CK-MB was less sensitive to nonspecific adsorption related interferences, had a better detection limit, and required a lower volume of sample than the SPR method.

Cardiac markers: a clear cause for point-of-care testing

Point-of-care testing (POCT) in patients with ischemic heart disease is driven by the time-critical need for fast, specific, and accurate results to initiate therapy instantly. According to current guidelines, the results of the cardiac marker testing should be available to the physician within 30 min ("vein-to-brain" time) to initiate therapy within 60-90 min ("door-to-needle" time) after the patient has arrived at the emergency room or intensive care unit. This article reviews the current efforts to meet this goal (1) by implementing POCT of established biochemical markers such as cardiac troponins, creatine kinase MB, and myoglobin, in accelerated diagnosis and management workflow schemes, (2) by improving current POCT methods to obtain more accurate, more specific, and even faster tests through the integration of optical and electrochemical sensor technology, and (3) by identifying new markers for the very early and sensitive detection of myocardial ischemia and necrosis. Furthermore, the specific requirements for cardiac POCT in regard to analytical performance, comparability, and diagnostic sensitivity/specificity are discussed. For the future, the integration of new immunooptical and electrochemical chip technology might speed up diagnosis even further. However, every new development will have to meet the stringent method validation criteria set for corresponding central laboratory testing.

Decreasing lab turnaround time improves emergency department throughput and decreases emergency medical services diversion: a simulation model

BACKGROUND

The effect of decreasing lab turnaround times on emergency department (ED) efficiency can be estimated through system-level simulation models and help identify important outcome measures to study prospectively. Furthermore, such models may suggest the advantage of bedside or point-of-care testing and how they might affect efficiency measures.

OBJECTIVES

The authors used a sophisticated simulation model in place at an adult urban ED with an annual census of 55,000 patient visits. The effect of decreasing turnaround times on emergency medical services (EMS) diversion, ED patient throughput, and total ED length of stay (LOS) was determined.

METHODS

Data were generated by using system dynamics analytic modeling and simulation approach on 90 separate days from December 2, 2007, through February 29, 2008. The model was a continuous simulation of ED flow, driven by real-time actual patient data, and had intrinsic error checking to assume reasonable goodness-of-fit. A return of complete laboratory results incrementally at 120, 100, 80, 60, 40, 20, and 10 minutes was compared. Diversion calculation assumed EMS closure when more than 10 patients were in the waiting room and 100% ED bed occupancy had been reached for longer than 30 minutes, as per local practice. LOS was generated from data insertion into the patient flow stream and calculation of time to specific predefined gates. The average accuracy of four separate measurement channels (waiting room volume, ED census, inpatient admit stream, and ED discharge stream), all across 24 hours, was measured by comparing the area under the simulated curve against the area under the measured curve. Each channel's accuracy was summed and averaged for an overall accuracy rating.

RESULTS

As lab turnaround time decreased from 120 to 10 minutes, the total number of diversion days (maximum 57 at 120 minutes, minimum 29 at 10 minutes), average diversion hours per day (10.8 hours vs. 6.0 hours), percentage of days with diversion (63% vs. 32%), and average ED LOS (2.77 hours vs. 2.17 hours) incrementally decreased, while average daily throughput (104 patients vs. 120 patients) increased. All runs were at least 85% accurate.

CONCLUSIONS

This simulation model suggests compelling improvement in ED efficiency with decreasing lab turnaround time. Outcomes such as time on EMS diversion, ED LOS, and ED throughput represent important but understudied areas that should be evaluated prospectively. EDs should consider processes that will improve turnaround time, such as point-of-care testing, to obtain these goals.

Point-of-Care Testing and Cardiac Biomarkers: The Standard of Care and Vision for Chest Pain Centers

Point-of-care testing (POCT) is defined as testing at or near the site of patient care. POCTdecreases therapeutic turnaround time (TTAT), increases clinical efficiency, and improves medical and economic outcomes. TTAT represents the time from test ordering to patient treatment. POC technologies have become ubiquitous in the United States, and, therefore,so has the potential for speed, convenience, and satisfaction, strong advantages for physicians, nurses, and patients in chest pain centers. POCT is applied most beneficially through the collaborative teamwork of clinicians and laboratorians who use integrative strategies, performance maps, clinical algorithms, and care paths (critical pathways). For example, clinical investigators have shown that on-site integration of testing for cardiac injury markers (myoglobin, creatinine kinase myocardial band [CKMB],and cardiac troponin I [cTnI]) in accelerated diagnostic algorithms produces effective screening, less hospitalization, and substantial savings. Chest pain centers, which now total over 150 accredited in the United States, incorporate similar types of protocol-driven performance enhancements. This optimization allows chest pain centers to improve patient evaluation, treatment, survival, and discharge. This article focuses on cardiac biomarker POCT for chest pain centers and emergency medicine.

An Enzyme Immunoanalytical System Based on Sequential Cross-Flow Chromatography

A new enzyme immunoanalytical concept that can be used for point-of-care testing has been investigated. Enzyme as a tracer requires a separate reaction step for signal generation, which follows the completion of immune complex formation with analyte (e.g., Hepatitis B surface antigen) in a sample. This has been a major factor limiting its utilization within the laboratory. We carried out such sequential processes employing chromatographic analysis, using two crosswise-arranged membrane pads in vertical and horizontal directions. The vertically arranged pads were the same as those in the usual format for pregnancy testing, for instance, with the exception of the use of horseradish peroxidase (HRP) as tracer. By placing the horizontally arranged pads on each lateral side of the signal generation pad in the vertical arrangement, they were employed to supply substrate to the enzyme present in the immune complexes. The substrate flow was initiated after the antigen-antibody bindings to produce a signal, which was typically a color change in proportion to the analyte concentration. Under optimal conditions, the use of HRP labeling increased the detection capability of the assay approximately 30 times compared to that of gold colloids. Potential advantages of using the concept investigated are (1) provision of a rapid and simple immunoassay, (2) satisfaction of a clinical need for highly sensitive determination of analyte, and (3) utilization of relatively inexpensive, portable quantitation means.

Appropriateness of point-of-care testing (POCT) in an emergency department

BACKGROUND

Acute coronary syndrome is a major cause of death, morbidity and access in emergency departments (ED).

METHODS

We evaluated a point-of-care testing (POCT) for the determinations of cardiac markers in an emergency department (ED), defining the clinical efficiency (management of patient with chest pain) and economic effectiveness (rationalization of preanalytical phase) related to data of Core Lab.

RESULTS

The results of analytical performances showed a good correlation (cTnI r(2)=0.89, myoglobin r(2)=0.84, CK-MB r(2)=0.9) between POCT and Core Lab and a significant decrease of the turn around time (TAT): difference of medians=-54 min, 95% CI from -48 to -60 min.

CONCLUSIONS

Our data confirmed that the accurate utilization of POCT in the ED assumes an effective triage of patient with chest pain and the improvement of preanalytical phase out of the laboratory (delivery of specimens) and within the laboratory reception, centrifugation. However, efficiency must be linked to methodological and quality control of the Core Lab, mainly through connectivity.