Hi Vipin:
As you know we too used the Stratus for Troponin I for several years and then switched to the Dade-Behring Dimension RXL, a main-line chemistry analyzer, about a year ago. Since I was involved in setting up a Troponin service on the Axsym at a neighbouring hospital, I can recount their experience which has not been entirely satisfactory. They began routine testing on the Axsym in April of this year and all seemed to be going well until around June when the first complaints of false positives were received from the clinical service. This turned out to be due to improper handling of the Axsym calibrators which have to be initially thawed, vortexed, incubated at RT for 3 hr, vortexed again, stored refrigerated and vortexed each time before use. It appears that each of these steps is critical to calibrator performance). Around September the onboard stability of the reagents deteriorated from the specified 366 days to 48 hours, with a calibration stability of 48 hr. They have been calibrating daily since then. According to Abbott the problem is related to the conjugate. The current policy is for them to refer all borderline results (0.5 - 2.0) to us for re-checking. We have noted undetectable results by our method in many of these specimens.
The cutoffs they use are: <0.5 (low probability of AMI), 0.5 to 1.0 (borderline; suggest repeat in 2 -4 hr), 1.0 - 2.0 (possible ischemia, cannot rule out MI; suggest repeat in 2-4 hr), >2.0 (consistent with AMI). These cutoffs are based on a 6 month "clinical experience" evaluation (unpublished).
I hope this information helps. Call me if you wish to discuss this further.
Mario D'Costa Ph.D. FCACB
Director of Clinical Chemistry and Core Lab
St. Joseph's Health Centre, Toronto
Assistant Professor, University of Toronto
Tel: (416) 530-6263
Fax: (416) 530-6559
Email: [log in to unmask]
>>> Vipin Bhayana <[log in to unmask]> 11/24 5:56 AM >>>
Does anyone has experience with troponin I on Abbott Axsym? As you know
the absolute values are quite different on different instruments. This
is mainly due to the antibodies that are used in the assay development
and lack of standardization. The measurement of Free TnI and complexed
TnI in different ratios by antibodies causes huge variation among TnI
assays. Abbott values are about 5 to 6 times higher than Dade Stratus
method. Can someone provide me the following information?
(1) What are the reference ranges or diagnostic cut-offs that you use in
your hospital for the Abbott TnI?
(2) What is the sensitivity and specificity at that diagnostic cut-off?
Do we get too many positives that we don't know what to do with them?
(3) What are the concerns that your ER physicians have with the Abbott
TnI? Too sensitive? Less sensitive?
(4) Do you use any comments with the TnI results?
I was using Stratus TnI (for the last 4 yrs) and I am now planning to
switch to Abbott within a month. The main reason being Stratus is
semi-automated and will be discontinued soon, Axsym easily accessible
for us in the core lab along with other immunoassays. Our clinicians
are quite satisfied with the performance of Stratus TnI. Don't know how
they will react to Axsym results?
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