A Proposed Change to CLIA

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The INR was an attempt to standardize accross platforms.  Thus the name.  But over the many years as a laboratory director, this has been the most difficult thing to explain to physicians, techs and unfortunately also to vendor reps.

Just pull your CAP competency and look at the acceptable ranges for INR with the same specimen.  The acceptable results are all over the place depending on platform and within Platform depending on reagent used.  The INR is hardly a standardizing ratio.

What is scary is that the reference ranges used does not reflect the differences in platform or reagents used.

Adjusting a patients dose using INR, utilizing different labs or methods within labs (Plasma vs POC) is bad practice.

Interesting. In both labs I work at we do not report INRs higher than a certain level. At the one lab, we use a Helena POC Cascade and the ISI is encoded on the barcode of the card so each lot will have a different INR that the instrument will report as greater than. At the other lab we use a Sysmex instrument and the ISI is very close to 1.0 and I believe we report up to 12 or 13. I guess I never thought too much about it, and I agree that both INRs are dangerously high and I was just surprised because I had never even heard of an INR as high as 28. Thanks for clarifying!

Shirley,

I agree! The treatment options are similar, so clinically the difference is moot. Often, it isn't a matter of looking at the flag to see if a result is normal or abnormal. Reference ranges, too, can be misleading. Docs interpret all this within the context of a clinical setting, and even that can be difficult as your great example points out.

I think we have a responsibility to improve our reports and refer patients to reliable sources. It's fine to tell a patient to ask his or her doctor, but these days it's naive to think the patient won't look up their results online before and after asking. Some of this is good; patients should partner with the healthcare team to understand what their issue is and why they are being treated. But much of it is bad or at least confusing. What looks "dumbed down" to professionals can still terrify a patient at a fifth- or sixth-grade reading level. More so when a loved one is involved!

A laboratory's reputation ironically depends on its accuracy, which varies lab to lab. We and the docs know this, but the public sees a number as a number. Or, at least one with very little variability. ("I started eating Cheerios and my cholesterol dropped ten points!") I have a feeling this will be interesting.

Andrea,

I thought so, too, but this is most true within a therapeutic range. The ISI is derived from a logarithmic curve, and what appears to be consistent variation on a logarithmic scale is magnified in linear practice. Some of our difference was in reagent sensitivity, too. At the time of the incident we used thromboplastin (high-ISI) and the other laboratory used a recombinant product (low-ISI) that is more sensitive. I don't recall the exact numbers, but the difference was dramatic.

CLSI acknowledges this difference, stating "Results exceeding an INR of 5.0 generally have reduced trueness, precision and linearity, both in POC and laboratory based PT testing." The WHO recommends calibrating a POC monitor using samples with INR values in the range of 1.5 to 4.5 for the same reason.

I suppose, it's easier to convince patients that tests should match between laboratories within a percentage, because most calibration curves are linear. That isn't really true for all INR values. Also, some patients will believe a bigger, more modern-appearing facility hires better and smarter people. It was a lesson for us!

We did a few things. Until we switched to a reagent with an ISI close to 1.0, we lowered our upper reportable INR to 9.0. It seemed unlikely we would correlate meaningfully above that limit with any method. We also implemented process changes to check integrity of and even recollect some samples with critical values. Unfortunately, for this patient the damage was done.

This is going to be difficult.  I always tell patients that I can give them the results, but the interpretation requires a physician.  And in the example given, both INR values are dangerously high - the treatment would be the same for both, either FFP or Vitamin K.  We recently made the decision to drop heparin Xa testing at our facility because our new instrument's values did not correlate well with our previous method.  The hospital across town uses our previous method and we wanted to avoid having very different results on the same test.

I thought the value of the INR was that it was standardized? The PT can vary but the ISI is implemented so that the INR will be the same no matter what method was used or where the test was performed? I am as confused as the patient.