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Serial change in troponin I aids in early diagnosis of MI

Reuters Health • The Doctor's Channel Daily Newscast

NEW YORK (Reuters Health) – In patients presenting with chest pain, troponin I levels measured on admission and at 3 hours reliably rule out or rule in acute MI — whether measured with a high sensitivity assay or a standard contemporary assay, a German team reports in the Journal of the American Medical Association for December 28th.

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.