hs-cTn Assays: A Game Changer? chest Pain Protocol, continued from page 6 Than added that demonstrating <strong>the</strong> value of a structured risk assessment was a key objective of ASPECT. “A lot of literature shows that assessments of pre-test probabilities are done extremely poorly by clinicians,” he observed. “In general, we tend to overestimate <strong>the</strong> risks because we’re concerned about <strong>the</strong> possibility of getting it wrong. We also tend not to agree with each o<strong>the</strong>r in assessing risk. That’s why we thought some sort of structured risk assessment was important.” The Role of High-Sensitivity cTn Assays While experts agreed that <strong>the</strong> ASPECT protocol broke ground by laying out objective assessment criteria <strong>for</strong> ACS, several observers questioned <strong>the</strong> relevancy of a POC panel employing CK-MB, myoglobin, and a contemporary—but not high-sensitivity— cTnI assay, given that both high-sensitivity cTnT and cTnI assays with limits of detection 10 times lower than conventional assays are about to hit <strong>the</strong> U.S. market (CLN Feb 2011). In addition, <strong>the</strong> cTnI assay used in ASPECT, <strong>the</strong> Alere Triage CardioProfiler, is not approved <strong>for</strong> use in <strong>the</strong> U.S. “There’s no question that ASPECT adds to <strong>the</strong> argument that myoglobin and CK- 8 CliniCal laboratory news July 2011 MB are no longer necessary,” said Wu. “In my opinion that conclusion was reached years ago, even be<strong>for</strong>e <strong>the</strong> advent of <strong>the</strong> current generation of troponin assays, but this reaffirms even more so that labs should move away from <strong>the</strong> <strong>for</strong>mer two.” Than explained that in his own clinical practice, he has not used myoglobin or CK-MB <strong>for</strong> at least a decade, but that <strong>the</strong> ASPECT investigators specifically wanted to evaluate a POC biomarker panel. “We were interested in <strong>the</strong> point-of-care concept, but we also felt that by using a slightly inferior troponin assay, one can say you can do this with any troponin assay you like—ei<strong>the</strong>r point-of-care or central lab— because even a less-sensitive assay works just fine,” he explained. “The main message of <strong>the</strong> paper was that <strong>the</strong> combination of this risk/pre-test probability tool, with ECG and troponin or combinations of biomarkers can be used <strong>for</strong> safe, early discharge of some patients. Whe<strong>the</strong>r <strong>the</strong> new high-sensitivity cTn assays will hinder or harm ef<strong>for</strong>ts to speed emergency department assessment of chest pain patients remains unclear. Some observers, like Michael Kontos, MD, argued that <strong>the</strong> assays will help quickly identify <strong>the</strong> lowest of low-risk patients but contribute Guidelines <strong>for</strong> managing acute coronary syndrome Patients Key professional organizations have published guidelines on <strong>the</strong> use and interpretation of cardiac biomarkers in aCs. acc/aha 2007 Guidelines <strong>for</strong> <strong>the</strong> management of Patients with unstable angina/non-sT-elevation myocardial infarction, J am Coll Cardiol 2007;50:e1–157. clinical Policy: critical <strong>issue</strong>s in <strong>the</strong> evaluation and management of adult Patients with non-sT-segment elevation acute coronary syndromes, annals of emergency Medicine 2006;48:270–301. nacb laboratory medicine Practice Guidelines <strong>for</strong> utilization of biochemical markers in acute coronary syndromes and heart failure, Clin Chem 2007;53:2086–2096. Testing of low-risk Patients Presenting to <strong>the</strong> emergency department with chest Pain: a scientific statement from <strong>the</strong> american heart association, Circulation 2010;122;1756–76. universal definition of myocardial infarction, J am Coll Cardiol 2007;50:2173–2195. in o<strong>the</strong>r ways to slower emergency department processing times. “You’ll have <strong>the</strong> really low-risk cohort where <strong>the</strong> troponin will be so sensitive that once you do <strong>the</strong> test and clinical assessment, you’ll essentially be able to exclude an acute coronary syndrome,” he said. “But <strong>the</strong>n you’ll have a more intermediate risk group that will have detectible troponin levels—not necessarily with serial changes or highly suggestive of acute coronary syndrome—but <strong>the</strong>y clearly need some sort of fur<strong>the</strong>r evaluation.” Kontos is associate professor of internal medicine at Virginia Commonwealth University’s Pauley Heart Center in Richmond. While high-sensitivity cTnI and cTnT assays might pose challenges in understanding just what very low levels of circulating cTn mean, Than suggested that when used with o<strong>the</strong>r components of <strong>the</strong> ASPECT protocol, <strong>the</strong> tests still would bring clarity and speed to emergency department-based chest pain evaluations. “There are far more patients who need to be ruled-out than ruled-in, and <strong>the</strong> way I see <strong>the</strong> high-sensitivity troponin assays working is that you’ll be able to set a slightly higher pretest probability to your risk score because <strong>the</strong> assay will be more sensitive,” he said. “This will enable you to incorporate a broader group of patients in a potential early rule-out group. There needs to be a greater awareness of rule-out and <strong>the</strong> benefits it can have on <strong>the</strong> healthcare system.” A Glimpse of <strong>the</strong> Future Most experts agreed that <strong>the</strong> high-sensitivity cTnT and cTnI assays eventually would lead <strong>the</strong> way towards shorter chest pain assessment protocols. “Conceptually, this a great model to consider, and it’s a good first step in thinking about whe<strong>the</strong>r assays will be able to differentiate chest pain patients this early in <strong>the</strong> process. The high-sensitivity troponin assays will narrow <strong>the</strong> window,” predicted Fred Apple, PhD, professor of laboratory medicine and pathology at <strong>the</strong> University of Minnesota School of Medicine, and medical director of clinical laboratories at Hennepin County Medical Center in Minneapolis. However, Apple cautioned that considerably more research would be needed be<strong>for</strong>e 2-hour chest pain work-ups become standard-of-care. “We’ll need a wealth of more in<strong>for</strong>mation be<strong>for</strong>e we start changing practice patterns. The high-sensitivity troponin assays will need to be looked at <strong>for</strong> baseline and two hours <strong>for</strong> every person who walks in <strong>the</strong> emergency department with suspected acute coronary syndrome, and determine whe<strong>the</strong>r an absolute value or delta change percent is best <strong>for</strong> patient triage. This is not ready <strong>for</strong> primetime just yet.” Research ef<strong>for</strong>ts that might trans<strong>for</strong>m chest pain assessment standards already are underway. For example, a team of British researchers recently reported that patients with suspected MI who were tested at presentation and after 90 minutes with a POC biomarker panel consisting of cTn, CK- MB, and myoglobin had shorter median, but not mean, lengths of stay in <strong>the</strong> emergency department and were discharged more frequently without inpatient admission (Heart 2011;97:190–196). In addition, Amsterdam and his colleagues at UC Davis are preparing to publish results from an accelerated assessment process <strong>for</strong> very low risk patients. “We’ve been investigating a protocol that involves a clinical assessment, biomarkers, and ECG with a two-to-four hour period,” he said. “It’s a minority of our population, but we’ve found <strong>the</strong> patients we’re doing this with to be very safe with no events at 30-days.” Than also has initiated a randomized controlled trial using <strong>the</strong> ASPECT protocol but with a central lab-based cTn assay. “I wouldn’t expect anyone to change <strong>the</strong>ir practice necessarily based on <strong>the</strong> ASPECT study, but I might expect <strong>the</strong>m to take more interest when results from this second study become available,” he said. “We expect that we’ll demonstrate that you can send 15 to 20 percent of patients home early and safely, with an economic benefit in terms of bed days saved.” CLN
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