Inr Confusion

[ALCapshaw]

OK, I'll admit up front, I'm being lazy in asking this question before researching it, in the hope that someone already knows the answer(s).

Here's the question:

Since INR is a RATIO, my understanding is that is supposed to eliminate the variation in reagent sensitivity from the result, SO,
why do we still see a consistent difference between the ProTime instruments and the Coaguchek instruments?

I'm also wondering if a better way to characterize the differences might be RATIO or Percent as opposed to a simple subtraction difference.

The smallest difference I've seen between my ProTime instrument and my Coumadin Clinic's Coaguchek machine is 0.5 and the largest difference has been 2.0 ! I've had two high readings (4.2 and 4.5) from the Coaguchek machine that seem questionable to me.

The BIG question in my mind, is why do we still see any difference at all between the two instruments.

'AL'

 

[Michele]

INR Confusion

INR Confusion

Here are some comments on INR values from our in-house nursing staff at QAS. Hope this helps.

Nurse Talk ? (COMMENTS FROM OUR IN HOUSE NURSING STAFF)

Variations in INR between different labs and finger-stick tests

INR values are similar to comparing the different temperatures of Fahrenheit and Centigrade. The numbers are not the same but the temperature is.

Many clinical studies have been completed comparing the INR results obtained on the ProTime Microcoagulation System to the results obtained at a hospital lab and at a reference lab. Imprecision of the INR among different test systems is known and all of the studies show that the ProTime System compares to the reference lab as well as the hospital lab compares to the reference lab.

What this means to you is that if your monitor INR result do not seem the same as your lab INR, do not despair. When looking at large numbers of patients the INR results show a spread when different lab analyzers are used to compare split samples of blood from one patient. This spread will increase as the INR value increases from 2 to a higher value. The differences are usually not ?clinically significant?. In other words the different INR values may not change what your physician would decide in regard to your dose of Warfarin. When the difference is great enough to become clinically significant, it does not mean that one result is inaccurate. Both results are accurate based on the system used. Patients and physicians become rightly concerned when the comparison between the monitor and the lab is great enough to make a different dosing decision.

New home testing patients do not have enough testing data on the home monitor to establish the bias or trending pattern that would show the relationship between the home and lab systems. More than one comparison is needed to establish this relationship. Multiple data points will show a consistent bias or range of difference between the monitor and the lab. The physician can then establish an INR range appropriate for each patient regarding the system being used. It is rather like to comparing the different temperatures of Fahrenheit and Centigrade. The numbers are not the same but the temperature is.

Other factors can also affect the INR results. If you are using the ProTime System incorrectly the result can be wrong. For example:

1. If blood is obtained before the prompt is displayed initiating finger stick, the INR can be show as lower than it actually is.
2. If excessive pressure is used to collect the capillary blood sample the result can be affected.
3. If the alcohol or water is not wiped off the finger and mixes with the blood sample, the result can be wrong.
4. Patients with some hypercoaguable disorders have a greater variability between INR lab results.
5. If low molecular heparin or lovenox is used within 30 minutes before the finger stick the monitor may show a high INR.

There are many more areas that the lab test can be affected by outside influences. For example:
1. During the lab draw, a specific amount of blood is needed to mix with the solution in the tube to match the ratio used to compute the INR. Inaccurately filled tubes will have a different INR.
2. After drawing the blood into the tube, the solution must be mixed with the blood and shaking to hard will affect the end result.
3. If the storage temperature is not correct, the result is affected.
4. When running the test, chemicals need to be added and inaccurate amounts will change the INR value.
5. A long period of time between the lab draw and when the test is run, will affect the lab value.


QAS and the manufacturer, ITC, encourage gathering enough data to be able to make an informed decision. The level of quality control built into ever test makes the ProTime System highly accurate and safe to use in the home.

 

[Blanche]

Al:
After you've read the "Nurse Talk" article from QAS, if you still want information on the International Normalized Ratio (INR),
perhaps the following will help.

www.compunetlab.com./home/publication/1101d
www.medicine.ucsf.edu/htc/clinicians/clin.inr
www.enw.org/Research-INR

I'm sorry that I don't know what you mean when you say, "I'm wondering if their is a better way to characterize the might be RATIO or Percent as opposed to a simple subtraction difference."
While you might see a consistent difference between your ProTime machine and one Coagucheck machine, that would not generalize to all ProTime and Coagucheck machines. The Director of Clinical Research at ITC once told me that she had reports from labs that showed that sometimes the Protime was higher than the Coaguchek, sometimes the Protime was lower than the Coaguchek, and sometimes they gave the same INR. It's been said on this board that it isn't rocket science, and it isn't, sadly.
It's like machine shop. There's a certain amount of "tolerance" that is expected, a plus or minus factor, if you will. It isn't the best system, but it's better than it was before the INR calculation was developed, it works very well, and it is all we have.

My husband went through the process of comparing two ProTime machines and two different labs, with the guidance of trained, medical professionals who were experts on the ProTime machine and other methods. His doctor demanded it, so we did it. And, they all differed all the time. I think he must have done at least l5 different side-by-side comparisons. In the end, we took the advice of one on this board that said, you have to have confidence in the method you choose. Albert chose the ProTime. I know how very frustrating this can be. I wish you all the best and hope you will find sufficient, reliable information so that you too can be confident in the method you choose.

Kind regards,
Blanche

 

[Blanche]

Al:
I don't know what the heck happened with the links I left. The first one is just fine. I have no idea what the second one is. When I try the link, I get something entirely different. I also seem to get through on the third one. One more time...you may want to try this one

www.wwnurse.com/Nurse-zine/Articles/coagulation.

 

[Granbonny]

Excessive pressure?

Excessive pressure?

Michele, I do have Hubby to push the red clip to incise my finger..Will my INR be higher or lower? IF, he presses real hard? Bonnie I have been in range for 3 times in a row..every 2-3 weeks..so guess I'm o.k. with his pressing hard. Bonnie

 

[Michele]

Pressure

Pressure

Bonnie,
We encourage our ProTime users to use FIRM pressure when incising their finger. I don't think you have anything to worry about because your INR readings are in therapeutic range.

 

[ALCapshaw]

Blanche -

Thank you VERY MUCH for those most informative links. It is clear that the higher the ISI, the greater the disparity in INR for small variations in PT ratio. This would seem to favor the ProTime instrument since my understanding is that they use reagents with an ISI = 1 vs. Coaguchek which is reported to use an ISI = 2, which can exacerbate numbers at the high end of the range. This is consistent with the two 'somewhat' (questionable?) high readings (4.2 and 4.5) I've had from the Coaguchek machine at my Coumadin Clinic.

Michele -

The only test condition in your list that might apply to my situation would be the use of "excessive pressure" with the finger stick. In my (Engineering) opinion, the required activation pressue for the Tenderletts is 'too high'. After removing the outer cover of a Tenderlett, I see that the Trigger pushes on a Lever which rests on a ridge behind the Incizer Blade. When sufficient pressure is applied to this Lever, the Lever flexes and slides down an incline behind the Blade. Again, in my 'opinion', the ridge behind the Blade is slightly too long. If it was made just a hair shorter, the Tenderlett would activate with LESS pressure applied to the trigger. I realize this is a trade-off.
It it triggers TOO easily, the liklihood of a 'premature' trigger action increases and Tenderletts may be triggered before they are even in place. While it is possible to 'reset' the trigger, I'm sure as a supplier, you would NOT want to advise this across the board to all users.

'AL'

 

[Michele]

Tenderlett

Tenderlett

Al,
You are right the manufacturer doesn't advise "retriggering" the Tenderlett due to the fact of infection, etc. Most people love the Tenderlett because the pendulum swing of the surgical steel blade is virtually a painfree way of lancing.