Abbott i-STAT 1 System Manual page 532

Interfering substances (such as heterophilic antibodies, non-specific proteins, or hCG-like substances)
may falsely depress or falsely elevate results. These interfering substances may cause false
18,27,28
results over the entire range of the assay, not just at low levels. 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 test
results are inconsistent with clinical information. In these cases results should be confirmed by an
alternate hCG method.
22
Specimens from patients who have received preparations of mouse monoclonal antibodies for
diagnosis or therapy may contain human anti-mouse antibodies (HAMA). Such specimens may
demonstrate either falsely elevated or falsely depressed results when tested with assay kits which
employ mouse monoclonal antibodies. These specimens should not be tested with the i-STAT
23,24
β-hCG assay.
Unknown interferences from medications may affect results.
Hook effect: no significant hook effect detected in samples up to 300,000 IU/L.
Partially clotted samples can result in elevated hCG results as well as quality check codes. To prevent
clotting in samples collected in heparinized tubes, 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 hCG or quality check codes.
The β-hCG assay has been characterized in whole blood samples with hematocrit levels up to 55%
PCV. Imprecision exceeding 10% (CV) has been observed for samples with hematocrit levels above
50% PCV.
The handheld must remain on a level surface with the display facing up during testing. Motion of the
handheld during testing can increase the frequency of suppressed results or quality check codes.
A level surface includes running the handheld in the downloader/recharger.
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 (2286 meters) above sea level. Where unavailability of
results is unacceptable, Abbott Point of Care recommends having an alternate test method available.
Prior to filling the i-STAT β-hCG cartridge, invert the blood collection tube and inspect for red
cell sedimentation. If sedimentation is observed, continue mixing by repeated inversion until the
sedimentation is no longer apparent. Samples from β-hCG positive patients or patients undergoing
hormone therapy may have higher erythrocyte sedimentation rates (ESR) which, if not tested
immediately, could cause visible red cell sedimentation at the bottom of the collection tube.
29,30
β-hCG
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Art: 730474-01D Rev. Date: 24-Jan-17