In fact, they found, “Various early biomarkers representing different aspects of an evolving ACS are less sensitive than cardiac troponin I for timely diagnosis of MI.”
Dr. Stefan Blankenberg, with University Heart Center Hamburg, and colleagues note that the detection of low levels of troponin I with new highly sensitive assays inevitably leads to reduced specificity in diagnosing acute MI. Use of troponin kinetics might overcome that problem.
The team therefore conducted a study of the performance of a new highly sensitive troponin I (hsTnI) assay in diagnosing MI, based on baseline levels combined with changes in levels after 3 hours, in 1818 consecutive patients admitted to the emergency department with suspected acute coronary syndromes.
The hsTnI assay with a level of detection of 3.4 pg/mL was compared with a contemporary assay (cTnI) that had a detection level of 10 pg/mL.
A final diagnosis of MI was made in 413 of the patients (22.7%). Using the 99th percentile as the cutoff for discrimination of acute MI, the admission hsTnI level had a sensitivity of 82.3% and a negative predictive value of 94.7%. Corresponding figures for cTnI were similar at 79.4% and 94.0%, the researchers report.
They found that using levels measured at 3 hours after admission increased the sensitivity to 98.2% and the NPV to 99.4%, for both assays.
For ruling in acute MI, the positive predictive value at admission was 75.1% with the hsTnI assay and 80.9% with the cTnI assay. When combined with the 3-hour measurements, these figures increased to 95.8% and 96.1%, respectively.
The investigators also measured several other biomarkers, such as glycogen phosphoprylase BB, copeptin, and growth differentiation factor 15, as well as classic necrosis factors CK, CK-MB and myoglobin. “In our study, the diagnostic information of hsTnI was superior to all other evaluated biomarkers alone,” Dr. Blankenberg and colleagues report.
Summing up, they conclude: “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%, 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.”
SOURCE:
JAMA 2011;306:2684-2693.
