cTnI - 6 Art: 715595-00R Rev. Date: 23-May-12
Test Limitations
The frequency of suppressed results is affected by atmospheric pressure. Suppressed result rates may
increase with higher elevations (decreased barometric pressure) and may become persistent if testing is
performed at more than 7500 feet above sea level. Where unavailability of results is unacceptable, i-STAT
recommends having an alternate test method available.
Samples from patients who have been exposed to animals or who have received therapeutic or diagnostic
procedures employing immunoglobulins or reagents derived from immunoglobulins may contain antibodies,
e.g. HAMA or other heterophile antibodies, which may interfere with immunoassays and produce erroneous
results.
18-24
The generation of potentially interfering antibodies in response to bacterial infections has been
reported.
16
While this product contains reagents that minimize the effect of these interferents, and QC
algorithms designed to detect their effects, the possibility of interference causing erroneous results should
be evaluated carefully in cases where there are inconsistencies in the clinical information. Results from the
i-STAT cTnI assay should be considered in the context of the entirety of the available clinical information.
Medical decisions should not be based on a single i-STAT measurement.
14
Cardiac troponin may not appear in circulation for 4-6 hours following the onset of symptoms of MI.
Consequently, a single negative result is insufficient to rule out MI. The use of a serial sampling protocol is
recommended practice.
11
The results of different troponin assays are not generally comparable: cTnI and cTnT are distinct molecules
and results are not interchangeable, nor comparable. In addition, significant variation in absolute troponin
values may be observed for a given patient specimen with different analytic methods.
13
Partially clotted samples can result in elevated cTnI results above the reference range, as well as quality
check code errors. To prevent this from occurring, upon drawing the whole blood sample into a heparinized
collection tube, the sample should be inverted gently at least 10 times to ensure even dissolution of the
heparin anticoagulant.
Grossly hemolyzed samples can cause a decreased alkaline phosphatase activity, resulting in decreased
detection of cTnI, increased assay backgrounds, and/or quality check codes.
Hematocrits in the range of 0-65 % PCV have been demonstrated not to affect results. Samples with
hematocrit levels above this range have demonstrated increases in the test imprecision and quality check
codes.
The analyzer must remain on a level surface with the display facing up during testing. Motion of the analyzer
during testing can increase the frequency of suppressed results or quality check codes. A level surface
includes running the handheld in the downloader/recharger.
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