NEW YORK (360Dx) – Researchers in New Zealand have reported that an Abbott point-of-care assay that measures troponin concentration can rule out acute myocardial infarction and produce a test result in 15 minutes from a single sample with discrimination capability comparable to that of a high-sensitivity troponin laboratory assay.
The researchers presented an initial analysis today in JAMA Cardiology of a preliminary cohort that was part of an Australia and New Zealand observational study. Their objective was to determine the clinical accuracy of the Abbott i-Stat TnI-Nx troponin test and compare it with the accuracy of the firm's Architect hs-cTnl high-sensitivity troponin assay for ruling out AMI.
The TnI-Nx point-of-care test is an enzyme-linked immunosorbent assay that improves detection of troponin I using paramagnetic beads and electrochemical detection of an enzyme signal coming from a sample of either plasma or whole blood.
Emergency department investigations of patients with suspected acute myocardial infarction are time consuming, partly because of the turnaround time of laboratory tests.
Current point-of-care troponin assays shorten turnaround times but lack precision at lower troponin concentrations, the researchers said, adding that development of point-of-care troponin assays with greater analytical precision could reduce the decision-making time in emergency departments for ruling out AMI.
In its study, the research group compared the clinical discrimination ability of the point-of-care assay with that of its laboratory counterpart using the area under receiver operator characteristic curve (AUC) and sensitivity, negative predictive value, and the proportion of negative test results at thresholds with 100 percent sensitivity.
Of 354 patients, 85 presented to the emergency department less than three hours after the onset of symptoms. Seventy two percent of the patients were men with a mean age of 62 years. Fifty-seven of the men, or 16.1 percent, experienced an AMI.
The researchers said that they found no difference between the AUC of the point-of-care and laboratory assays in their analysis. The point-of-care assay running on an i-Stat blood analyzer and testing at a concentration of 11 ng/L identified 201 patients, or 56.7 percent of the population, as being at low risk, with a sensitivity of 100 percent and a negative predictive value of 100 percent. By comparison, the laboratory troponin assay testing patients with a concentration of less than 3 ng/L identified 154 patients, or 43.5 percent, as being at low risk, with a sensitivity of 100 percent and a negative predictive value of 100 percent.
The researchers noted that the lowest TnI-Nx concentration on presentation in any patient with an AMI was 11 ng/L, and the lowest hs-cTnI concentration of any patient with AMI was 3 ng/L.
The researchers reported that as a result, the point-of-care assay using one blood sample can produce a result in 15 minutes that has comparable discrimination capability to an hs-cTnl assay for ruling out AMI. Use in the emergency department could expedite the safe discharge of a large proportion of low-risk patients, the researchers said in the paper.
"When designing Abbott's newest point-of-care cardiac test, we wanted to combine the benefits of higher sensitivity troponin tests with the speed of results when it matters most," said Matt Bates, divisional vice president of research and development for point-of-care diagnostics at Abbott. "This initial data will help guide our research and development of the next generation of cardiac testing to help physicians and emergency departments make timely decisions with confidence."
Laboratory-based high-sensitivity cardiac troponin assays have been shown to have enough accuracy at low concentrations to enable AMI to be ruled out in a large proportion of patients after analysis of just one blood sample taken when a patient presents to the emergency department.
But turnaround time remains an issue for such lab-based tests, especially the time needed to transport the blood to a central laboratory and subsequent centrifugation to prepare a plasma sample.
The use of troponin assays at the point of care eliminates the transport step. However, point-of-care cardiac troponin assays that use whole blood and speed analysis to less than 15 minutes have lacked the clinical precision required at very low concentrations of the troponin protein, the researchers said.
To rule out an acute myocardial infarction, clinicians need to be able to accurately read levels of troponin, which are elevated in the bloodstream after damage to the myocardium, the middle and thickest layer of the heart wall.
The research group conducted its study in patients recruited between July 2016 and January 2018 at a regional, general and tertiary metropolitan emergency department in Christchurch.
"The results suggest that the TnI-Nx assay has similar clinical sensitivity to hs-cTn assays to accurately enable early rule-out after a single baseline blood sample," the researchers said in their paper. "This is important because it means that it may be possible to safely rule out AMI within 15 minutes of blood draw in the ED for a substantial proportion of patients."
They noted that the point-of-care assay could also be useful outside the emergency department in ambulances, and in rural hospitals and general practices where there is limited access to laboratory-based troponin assays. A point-of-care assay able to accurately rule out AMI may prevent long and unnecessary transfers to secondary hospitals, they said.
However, the research group cautioned that it does not describe the point-of-care assay as having high sensitivity "because that has not yet been established."
Further, they cautioned that the study "should be regarded as preliminary" because the study cohort was small and analyzed by a single adjudicator. They didn't present a positive predictive value because the report focused on "very early rule-out of AMI" and the reference range and 99th percentile of the assay are yet to be established."
Lab-based high-sensitivity troponin tests have been in use in Europe for years, but they have been cleared in the US only recently. Roche received FDA clearance for its test in early 2017, while Beckman Coulter's high-sensitivity troponin test was cleared this past June. Siemens received clearance for its test the same month.
Abbott announced in September that it had received CE marking for its high sensitivity troponin I laboratory-based blood test running on the Architect system, to assess cardiac risk. According to the Abbott Park, Illinois-based firm, it marks the first troponin test with CE marking that can more accurately predict — potentially months or even years ahead of time — whether a person may have a heart attack or other cardiac event. The test is pending clearance from the FDA.