i-STAT Troponin testing
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We are in the process of moving our Urgent Care Clinic to a stand-alone clinic outside of the hospital. The UCC medical director would like to implement troponin testing on the i-STAT. Does anyone have experience with this? What pros/cons could you offer?
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Make sure everyone understands that methodology and sensitivities are different and you cannot compare the quantitative results of the iSTATs to the main lab analyzers. Troponin serial testing should start and finish with the SAME analyzer and you cannot switch back and forth from one analyzer (POC) to another (lab). You should also think about what cutoff values for positives you would use (99th percentile??) The lab analyzer may have a different cutoff which can cause confusion. Sample integrity is important so make sure everyone knows to fill tubes to capacity, no hemolysis or clots since these all affect the accuracy of the test results. If you have AQF, implement QC scheduling and lockout if not performed.
We have no issue with iSTAT Troponin correlating with our Beckman DxI Troponin, with the exception with heterophile antibodies.
Our I-Stat Troponins do not correlate with our Vista lab analyzer. Abbott said it be like comparing apples and oranges. We now do our correlations as followed:
I-Stat Troponin Correlations
Device:
I-Stat
Vista
Positive Values:
≥0.08ng/ml
≥0.045ng/ml
Negative/Normal Values:
<0.08ng/ml
<0.045ng/ml
We correlate if they both were either positive or negative based on the above ranges. This was confirmed to be acceptable with CAP as long as its noted in our procedure.
The iSTAT is easier to use, and it is hand held. If you can use a small desk top, I would recommend looking at the Pathfast Analyzer that is now owned by Polymedco. (All troponins are moderate complexity.) Both products offer challenges with validating linearity. Neither offers a product that goes down to the full range of linearity. In fact, one reason I d/c the iSTAT was because they offered NO commercial negative value for control or calibration verification.
We use WSLH’s proficiency to prove 0.00 for troponin.
On a study we just did, there were 10% false negatives on the ISTAT. One of the other hospitals in town got a 20% false negative o the ISTAT. What I would ensure is that the clinicians know about this, and that they follow the idea of once you do a troponin on one platform that you should follow the patient on the same platform for the duration.
Deanna Bogner
210-297-9657
Deanna Bogner,
What analyzer do you use in your main lab? Is you assay effected by biotin?
Jeremy,
We use Abbott not Roche. As far as I know, biotin is not an issue with the analyzer in the lab.
I question the definition of "false negative" when it comes to Troponin I in the ED - just because the iSTAT got a result below 0.08 and the lab got a result above 0.045 on the same sample does not mean the iSTAT was wrong. The test is supposed to be ruling in or out for Acute Myocardial Infarction. A true false negative results would mean the above is true AND the patient was actually having a heart attack. I saw all the time where the lab results were slightly elevated but not "positive" per se - they were "abnormal" and stayed that way for several consecutive readings possibly due to an antibody or that was just that person's normal. I think there is a fault to the higher sensitivity analyzers in the lab that are from my experience, causing a lot of unnecessary trips to the cath lab, where the iSTAT is better at catching true disease and is therefore more SPECIFIC to AMI.
If you really want to get into the weeds, we did a ROC study for iSTAT vs Lab Troponin several years ago that was very telling and gave me a lot more confidence in the iSTAT method. However, as mentioned above, if your ED doc's think that it is ok to toggle back and forth between iSTAT and Lab as though they were the same test, you will have a big headache on your hands - they need to pick a method and trend on it, don't do an iSTAT at arrival, then a lab at 1 hour, then an iSTAT at 2 hours, then a lab at 4 hours - and try to trend them as the same test. Make sure your iSTAT Troponin is distinguished in the medical record as a completely different test, on its own line, such as "POC Whole Blood Troponin" and has it's own reference range - do not use the lab's reference range!
Silka,
"false Negative" does not mean the ISTAT is wrong...I agree. You can make the case that the both the lab and the ISTAT are faulty since they do not match. You would over treat on the lab and possibly under treat on the ISTAT.
I know of cases where a "clean cath" has been performed on patients using a lab method or the ISTAT method in places other than my hospital.
The other part of this is that for the most part, the patients that present as a heart attack (EKG, symptoms) per the ER doc, most of the time they do not wait for the troponin. Those people are trucked to the Cath Lab
As it was explained to me by the ER docs, it is the people in the middle of the Bell Curve that the POCT troponin is the most useful to perform rule in/rule out triage. They described to me some cases that the patient was having a heart attack, but the initial complaint was a "tooth ache", or "my left thumb hurts". I asked the doc, "So the possibility of the false negative on the ISTAT would not bother you?" For the most part the doc said, they will use the lab. He said that the ISTAT "gives them an idea" of what they might be facing.
In some cases, ED POCT Troponins are used not only to triage the patient, but also to meet the metrics of the 0-60 minutes for first troponin for the chest pain accreditation, if that is in place at your hospital.
As long as the docs know/understand what the differences are in the methods with that comparison, and use it in that manner, use one method as their baseline, and continue to use the same method to follow the patient, all is well.
Deanna Bogner 210-297-9657
Troponin. There have probably been more instances where the iSTAT became positive before the main lab assay did. We do have lots of old school docs that still order the main lab Troponin, but hospital accreditation is pushing the POC test for better turn around
time.
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I confess, since moving to Children's Hospital last year I have been doing the happy dance because I no longer have to worry about Troponin!! I lived and breathed Troponin for years, and now I am finally FREE :)