According to a study in the December issue of JAMA, using a contemporary or highly sensitive test for levels of the biomarker troponin I, a protein in the muscle tissue, in patients admitted to emergency departments with chest pain, could potentially assist in ruling out a diagnosis of a heart attack. Changes in the levels of the biomarker 3 hours after the patient's admission may prove beneficial to confirm a diagnosis of a heart attack.
Acute chest pain is one of the most frequent reasons for patients to seek care in an emergency department. The researchers write that:
"Early identification of individuals at high and intermediate risk for myocardial ischemia [insufficient blood flow to the heart muscle] is crucial because they benefit the most from early and aggressive treatment. According to international consensus and task force definitions of myocardial infarction [(MI; heart attack], the diagnosis of MI is based mainly on an elevated cardiac troponin level exceeding the 99th percentile and demonstrating an increase or decrease over time."
Researchers have recently developed highly sensitive troponin assays, which can safely evaluate troponin levels in over 50% of the general population. Assays are procedures in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample.
The researchers write:
"The reliable detection of very low troponin concentrations using these new highly sensitive assays in the acute setting might pose a challenge in everyday clinical practice."
Till Keller, M.D., of the University Heart Center Hamburg, Germany, and his team decided to assess the diagnostic performance of the newly developed highly sensitive troponin I (hsTnI) assay compared with a contemporary troponin I (cTnI) assay. They also examined the serial changes in the diagnosis of heart attacks. The researchers assessed a total of 1,818 patients with suspected acute coronary syndrome, such as heart attack or angina, who were enrolled at chest pain units in Germany from 2007 to 2008 and measured twelve biomarkers including hsTnI and cTnI on admission and after 3 and 6 hours.
On discharge, 413 patients (22.7%) had a final diagnosis of acute MI. The researchers discovered that both hsTnI and cTnI assays proved superior to the other evaluated diagnostic biomarkers to identify patients with acute MI.
On admission, findings of the hsTnl assay using the 99th percentile cutoff displayed a sensitivity of 82.3% and negative predictive value (NPV) of 94.7%, whilst after 3 hours hsTnI showed a sensitivity of 98.2% with NPV of 99.4%. When hsTnl was compared with cTnl assay using the 99th percentile as cutoff, they observed a similar sensitivity and NPV of 79.4% sensitivity and 94.0% NPV on admission, and 98.2% sensitivity and 99.4% NPV after 3 hours.
The researchers write:
"Combining the 99th percentile cutoff at admission with the serial change in troponin concentration within 3 hours, the positive predictive value (for ruling in AMI) for hsTnI increased from 75.1 percent at admission to 95.8 percent after 3 hours, and for cTnl increased from 80.9 percent at admission to 96.1 percent after 3 hours.
The shortcoming of conventional troponin assays with low sensitivity within the first hours after chest pain onset led to the evaluation of various so-called early biomarkers in the diagnosis of MI. In our study, the diagnostic information of hsTnI was superior to all other evaluated biomarkers alone."
"Use of hsTnI and cTnI assays in patients with suspected MI provides useful diagnostic information. Determination of hsTnI and cTnI values 3 hours after admission to the emergency department with use of the 99th percentile cutoff provides an NPV greater than 99 percent, potentially allowing a safe rule-out of MI. Application of the relative change in hsTnI or cTnI concentration within 3 hours after admission in combination with the 99th percentile diagnostic cutoff value on admission improves specificity and may facilitate an accurate early rule-in of MI."
Written by Petra Rattue