Abbott i-STAT 1 System Manual page 494

Metrological Traceability
The i-STAT System test for cardiac troponin-I (cTnI) measures cardiac troponin-I amount-of-substance
concentration in plasma or the plasma fraction of whole blood (dimension ng mL ) for in vitro diagnostic
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use. Cardiac troponin-I values assigned to i-STAT's controls and calibration verification materials are
traceable to i-STAT's working calibrator prepared from human cardiac troponin-ITC complex (Hy-Test
Ltd., Turku, Finland, catalogue #8T62). i-STAT System controls and calibration verification materials are
validated for use only with the i-STAT System and assigned values may not be commutable with other
methods. Further information regarding metrological traceability is available from Abbott Point of Care
Inc.
Reportable Range
The i-STAT cTnI test will report 0.00 to 50.00 ng/mL (μg/L). Samples above the reportable range will yield
">50.00 ng/mL" on the analyzer display screen. However, the performance characteristics of the i-STAT
cTnI measurement have not been established for cTnI values above 35.00 ng/mL (μg/L).
Reference Range
Whole blood and plasma samples from 162 apparently healthy donors were assayed in duplicate using
three different lots of i-STAT cTnI cartridges. The 0 to 97.5% range of results spanned 0.00 ng/mL (μg/L)
to 0.03 ng/mL (μg/L). The 0 to 99% range of results spanned 0.00 ng/mL (μg/L) to 0.08 ng/mL (μg/L).
Note: Each facility should establish its own reference range using the i-STAT cTnI assay.
Clinical Significance
Biochemical cardiac markers, including cTnI, are useful for both the diagnosis of myocardial infarction and
the risk stratification that can help guide the choice of therapeutic options.
For optimal diagnostic usefulness, a cardiac marker should be specific for cardiac tissue, should be rapidly
released into the bloodstream with a direct proportional relationship between the extent of myocardial injury
and the measured level of the marker, and should persist in blood for a sufficient length of time to provide
a convenient diagnostic time window. The cardiac-specific troponins, troponin I (cTnI) and troponin T
1
(cTnT) are considered the biochemical markers of choice in the evaluation of acute coronary syndromes
(ACS) including ST-elevation myocardial infarction, non-ST-elevation myocardial infarction, and unstable
angina. Elevated levels of cardiac-specific troponins convey prognostic information beyond that supplied
2,3
by the patients clinical signs and symptoms, the ECG at presentation, and the pre-discharge exercise test.
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Antman et al. reported that patients with elevated levels of cTnI had a statistically significant increase in
mortality (p< 0.001). Other studies have shown increases in other non-fatal cardiac events such as non-
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fatal MI, congestive heart failure, and urgent revascularization with increasing levels of cTnI.
5,6,7
The ability for cTnI to be measured at low concentrations allows therapeutic intervention to be considered at
any elevation above the normal range. Patients that present with no ST-elevation on their ECG but who have
even slight elevation in cTnI or cTnT may receive a greater treatment benefit from certain drugs such as GP
IIb/IIIa inhibitors or low molecular weight heparin.
8,9,10
A Global Task Force with joint leadership from the European Society of Cardiology (ESC), the American
College of Cardiology Foundation (ACCF), the American Heart Association (AHA) and the World Heart
Federation (WHF) refined past criteria of myocardial infarction with a universal definition of myocardial
infarction that supports the use of cTnI as a preferred biomarker for myocardial injury. The universal
definition of MI according to this task force is defined as a typical rise and gradual fall of cardiac biomarkers
(preferably troponin) with at least one value above the 99th percentile of the upper reference limit (URL)
together with evidence of myocardial ischemia with at least one of the following: ischemic symptoms,
pathological Q waves on electrocardiogram (ECG), ischemic ECG changes, or imaging evidence of new
loss of viable myocardium or new regional wall motion abnormality. An elevated troponin value alone is
2
not sufficient to diagnose a myocardial infarction. Rather, the patient's clinical presentation (history, physical
cTnI - 2
Art: 715595-01R Rev. Date: 01-Jul-13