Assessing the Role of Point-of-Care Cardiac Markers in the Emergency Department

Editor's note: This article is based on results of the RATPAC trial.

Point-of-care (POC) testing for cardiac markers has been advocated for many years as a way to expedite evaluation and treatment for emergency department (ED) chest pain patients.1,2 Although it seems intuitive that POC testing should decrease the ED length of stay and improve patient care, there are limited data demonstrating this. The Randomised Assessment of Treatment using Panel Assay of Cardiac Markers (RATPAC) trial3 was performed to determine the effect of using a POC cardiac marker panel in ED patients with possible myocardial ischemia.

A total of 2,243 patients with possible myocardial infarction (MI) were enrolled in this multicenter randomized trial, performed in six acute hospitals in the United Kingdom. High-risk patients (i.e., those with ischemic ECG changes, known coronary disease) were excluded, as were patients with an obvious noncardiac cause or other condition thought to lead to admission.

Using the Siemens Stratus CS analyzer, creatine kinase-myocardial band (CK-MB), myoglobin, and troponin I (TnI) were measured at baseline and 90 minutes, and compared with standard care (TnT at 6 hours [one center], or TnI at 12 hours after the worst symptoms [other five centers]). The TnI assay had a detection limit of 0.02 ng/ml and a 99th percentile of 0.07 ng/ml.

In this study, hospital admission was recommended for any TnI >0.02 ng/ml, any CK-MB level >5 ng/ml, and if the CK-MB increased by >1.6 ng/ml or the myoglobin increased >25% between the 0 and 90-minute sample. The TnI threshold for admission was later changed (to reflect current guidelines) to admission if either TnI was >0.07 ng/ml, or if the first sample was <0.03 ng/ml and the second was between 0.03 and 0.07 ng/ml.

The primary outcome was successful discharge home, and no major adverse events up to 3 months. Secondary outcome measures included length of stay, and a variety of measurements of care utilization, as well as adverse events.

Overall, POC panel assessment was associated with an increased rate of successful discharge (32% vs. 13%; p < 0.001) from the ED and reduced median length of initial hospital stay (8.8 vs. 14.2 hours; p < 0.001). However, when assessed at 24 hours, the difference in admission rate was no longer present. In addition, more patients in the POC arm were admitted to the critical care unit (4% vs. 2%; p = 0.001). Also, mean length of initial stay (30 vs. 32 hours; p = 0.46), mean inpatient days over follow-up (1.8 vs. 1.7; p = 0.83), and major adverse events (3% vs. 2%; p = 0.31) were not significantly different between the groups.

The authors concluded that POC panel assessment increases successful discharge home and reduces median length of stay, but does not alter overall hospital bed use.

Commentary

ED and hospital overcrowding is a problem that is not unique to the United States, as seen by this study from the United Kingdom. Because patients with chest pain make up approximately 10% of all ED evaluations, they represent an important group for intervention. As many of these patients are low risk, rapid exclusion of MI using POC testing offers the opportunity for accelerated decision making, allowing either discharge or provocative testing. By reducing the "vein-to-brain" time, the time it takes from when blood is drawn to when the physician has the results, treatment decisions should be made more rapidly.

Advantages of POC testing include reducing or eliminating the time needed for specimen transport to the lab, sample preparation, and data entry. In addition, because the test is performed in or near the ED, the delay related to the time when the results are entered and available to the clinician, to the time the clinician actually is aware of the results, should be reduced.

It should be recognized that POC testing is not without cost. Often the test costs are more expensive that if performed at a central laboratory. POC tests are expected to be as accurate, precise, and reliable as those performed at the central lab, despite being performed by multiple operators with varying experience. It can be difficult to manage POC testing and to maintain regulatory compliance, especially in large institutions. Finally, accurate notation of the results in the patient record for easy future reference may be difficult.

Therefore, it is important to demonstrate that the reduced turnaround time improves clinical decision making and patient management, or increases efficiency in evaluating and treating patients sufficient to offset the additional costs and logistical difficulties.

Prior studies, using combinations of cardiac makers, demonstrated that a POC strategy could accelerate the diagnostic process.1,2 Whether these led to meaningful changes in patient care was not clear. In addition, most were limited in using a relatively insensitive Tn assay, such that other markers were required to improve early diagnosis. Newer devices, with improved accuracy, may no longer require a multimarker approach, and instead may be able to rely on Tn alone.

Two other recent randomized trials have evaluated POC cardiac marker testing. In one trial, ED POC, Tn testing reduced time to anti-ischemic therapy and physician notification of Tn results by about 45 minutes, but did not change ED length of stay or patient outcomes.4 In another that included 2,000 patients, there was no difference in time to discharge home or time to transfer to an inpatient setting for admitted patients.5

Strengths of the current study are the inclusion of a large number of patients, the randomized nature of the trial, and exclusion of high-risk patients so that the patient population test was one where POC testing would likely be most beneficial.

Despite these strengths, the authors failed to find significant differences in many endpoints, including mean length of initial stay, mean inpatient days over follow-up, and major adverse events, although median length of stay was significantly reduced in the POC arm. The fact that coronary intensive care unit admissions were increased should give some pause. Failure to reduce all time measurements may result from POC testing being only one component of the evaluation, and other variables, such as other diagnostic testing required or limitations in availability of inpatient beds, negates any of the benefit.

Finally, some of the time reductions the authors found may be artificial and a result of the fairly long rule out process in the standard-of-care arm. A fairer comparison would have been to use the same strategy, but one with results available from the POC device and the other from the central laboratory.

The failure to demonstrate treatment benefits may be that in a low-risk patient population, there are insufficient numbers of high-risk patients in whom the time difference in treatment makes a difference in care that can be accurately measured. Given the study results, it does not seem likely that POC testing will be more rapidly adopted, but will depend more on unique features of the individual hospital.

One variable often not assessed in these studies that may be of critical importance to the ED is more rapid bed turnover, given the frequency of ED overcrowding. An economic analysis from these authors that is currently being prepared should provide additional information as to whether the potential benefits of POC testing justify the additional costs. The results of this analysis will be critical for better assessing the role of POC cardiac markers in the ED.


References

  1. Newby LK, Storrow AB, Gibler WB, et al. Bedside multimarker testing for risk stratification in chest pain units: the chest pain evaluation by creatine kinase-MB, myoglobin, and troponin I (CHECKMATE) Study. Circulation 2001;103:1832-7.
  2. Caragher TE, Fernandez BB, Jacobs FL, Barr LA. Evaluation of quantitative cardiac biomarker point-of-care testing in the emergency department. J Emerg Med 2002;22:1-7.
  3. Goodacre SW, Bradburn M, Cross E, Collinson P, Gray A, Hall AS, on behalf of the RATPAC Research Team. The Randomised Assessment of Treatment using Panel Assay of Cardiac Markers (RATPAC) trial: a randomised controlled trial of point-of-care cardiac markers in the emergency department. Heart 2011;97:190-6.
  4. Renaud B, Maison P, Ngako A, et al. Impact of point-of-care testing in the emergency department evaluation and treatment of patients with suspected acute coronary syndromes. Acad Emerg Med 2008;15:216-24.
  5. Ryan RJ, Lindsell CJ, Hollander JE, et al. A multicenter randomized controlled trial comparing central laboratory and point-of-care cardiac marker testing strategies: the Disposition Impacted by Serial Point of Care Markers in Acute Coronary Syndromes (DISPO-ACS) Trial. Ann Emerg Med 2009;53:321-8.

Clinical Topics: Acute Coronary Syndromes, ACS and Cardiac Biomarkers

Keywords: Acute Coronary Syndrome, Biological Markers, Chest Pain, Creatine Kinase, MB Form, Critical Care, Decision Making, Early Diagnosis, Electrocardiography, Emergency Service, Hospital, Follow-Up Studies, Inpatients, Intensive Care Units, Length of Stay, Limit of Detection, Myocardial Infarction, Myoglobin, Outcome Assessment (Health Care), Point-of-Care Systems, Troponin I


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