A Protime/Coagucheck question

[EVELYN]

Ok, back to the old INR (It's never right!!)

Today Tyce had to go to our cardio for an INR test.....His nurse checked him on 2 Coagucheck machines....their old and their new one. Both machines registered 5.0. When he came home, I checked him on our Protime....2.9. Of course they want him to withold for 2 days, which isn't going to happen, but I am beginning to doubt our Protime now. I have requested ITC to send me the plug which would reprogram our machine to an ISI of 2, which I believe is the standard used for the Coagucheck. Hopefully, that will solve the problem. What do ya'll think???

Evelyn

 

[EVELYN]

The saga continues. Our cardio's office just called and wants Tyce to go to our hospital for a lab draw stat. Maybe that way we'll know which one is closer!!! Will keep everyone posted on the third factor in the equation.

Evelyn

 

[catwoman]

Evelyn:

What is an ISI? I've applied to insurance for a ProTime but do want numbers to be as close to what they are on CoaguChek, which my PCP uses.

 

[tommy]

Evelyn,

Gosh, what a dilema! Been there. Had a three way check with the home test, coumadin clinic and local lab. I hate to tell you, but we never really got to the bottom of it.

But.........I was struggling a bit to transfer that drop of blood from my fat finger to that tiny little spot on the test strip. Whoever designed that procedure needs to be loaded up with rat poison and shot. The Roche rep got me some capillary tubes like they use at the clinic, Since then I have had no problem.

I'm also more diligent about cleaning the machine and my finger. Also use the control vials every time.

I have gotten to know the nurses in the cardios' office (also my coumadin clinic) pretty well. They indicated a couple of things. My lab test has a lot af variables due to transporting the blood miles in a vehicle to the lab. (Your hospital test shouldn't have that variable.) Using the capillary tube may give a slightly lower INR due to delay in transfering the boold to the strip. This should be minimal - it's what they do a the clinic.

Keep us posted.

 

[LDS4EVER]

INR LOW

INR LOW

HI, EVELYN,last week I had my INR level check at a local lab and the dr recieved his office called me back a week later right before he was closing ,the nurse said it was good I said well what are the numbers oh she said its 1.6 contuine to take the doses tht he has told you to take, but I know for a fact its too low I dont know what to do should I be my own dr and requalte my own doses I believe he is very inex perenced with coumadin therpy Im in the process of looking for a dr.who will accept government medi-cal I cant take this much more Im at my wits end this is my life they are dealing with i could have a stroke if its too low I was in the hospital in sept for having it too thin i ended up having 5 pints of blood to counter act the problem well thank you ,chris

 

[EVELYN]

Hello Catwoman
This is how I understand ISI to the best of my knowledge:

An ISI is the International Sensitivity Index which is assigned by the manufacturer of the reagent the particular machine uses. For example, Protime has an ISI of 1, Coaguchek, an ISI of 2. . I believe the ISI's range from 1-3, and the lower the reagent, the higher it's sensitivity to vitamin k dependent clotting factors. Mr. Al is the resident expert and can expand upon this, but that is what I understand from the manual Protime supplies.

Haven't heard from our cardio's office yet, but will keep you posted.

Ev

 

[EVELYN]

Back again



Just got a call from our cardio....the hospital lab draw was 4.9.....it looks as though our Protime is wrong and the coaguchek and hospital lab is right.....scary when it's your life that you're dealing with, isn't it!!!

I do have the plug being sent to me to reprogram our Protime. If it's not any better next Friday, I guess I'll have to start complaining to QAS....There's a big difference, in my opinion, from 2.9 and 5!!!Maybe I'm in the same boat as Rain was with her machine, who knows!!!

Evelyn

 

[EVELYN]

Chris....you have to be proactive when it's your life your dealing with!!!That's the bottom line as far as I'm concerned! Evelyn

 

[JimChicago]

Wow - and I was on the verge of getting a Protime machine.
Evelyn writes:
>>>>
I do have the plug being sent to me to reprogram our Protime. If it's not any better next Friday, I guess I'll have to start complaining to QAS....There's a big difference, in my opinion, from 2.9 and 5!!!Maybe I'm in the same boat as Rain was with her machine, who knows!!!
>>>>>
What is this plug? If they reprogram the Protime does that mean the ISI of 1 was in error? I wonder if a different batch of cuvettes would yield a different result?

 

[EVELYN]

Hi Jim

Yes, the plug is for professionals and just reprograms the Protime to be in line with an ISI of 2, which is what the Coagucheck uses. The isi of 1 is NOT an error, just what Protime uses. Coaguchek uses materials with an ISI of 2. I did call ITC and Tyce will retest this afternoon again with our Protime. If it's still way off, it is either the machine or the cuvettes. However, these are replacement cuvettes because we were called to send back our other set because they were faulty.....so who knows!

Confused and a bit irritated as this was a big investment monetarily and we thought we were buying the right brand. I don't think a quality machine should break after about 15 months of use weekly!!!

Evelyn

 

[Marty]

Coaguchek or Protime?

Coaguchek or Protime?

catwoman, my advice is get the same monitor your PCP uses, in this case Coaguchek.

 

[EVELYN]

Thank you Lance and ITC

I just got off the phone with both Lance from Qas and ITC in Jersey. ITC is sending me out both a new loaner unit and new cuvettes because they have no idea why the machine is doing this. Of course, I did mention that we were using NEW cuvettes that were sent to us because our last batch was defective and recalled. The new ones were NOT left out in the heat and went right into the refrig when they were delivered, so personally I don't think it's the cuvettes

We are to test both machines on Wednesday and record results and both machines with our cardio's office on Friday and do the same. Lakeesha from ITC is reprogramming the new unit with an ISI of 2 so it will be more in line with the Coaguchek, which our cardio uses.

I do hope we get to the bottom of this, and I thank God that Tyce didn't have any problems because of it. It certainly has made me feel very untrusting of this product. I would encourage everyone who has a machine to have it checked against a clinic or hospital draw routinely---I know we will from now on.

Evelyn

 

[JimChicago]

Thanks fo keeping us posted Evelyn.

My math is a bit rusty but as far as I can see if 2.9 is based on an ISI of 1 - then to get it to read 5 instead would mean an ISI of 1.5 (since the ISI number is the exponent in the INR equation. If the 2.9 is based on an ISI of 1 when 2.9 is raised by an ISI of 2 it would be 2.9 times 2.9 = 8.41.

I looked for some articles on the web about the ISI and they say the basic formula is:

INR = (PT time/mean PT time) ^ ISI (where ISI is the exponent)

The ISI is supposed to be established based on the different characteristics of the testing reagents so that the INR is a standard measure across all the different testing variables.

One question I would have is do both the coaguchek and Protime give both the INR and the PT time itself. If so you could at least see if both machines are reporting the same PT time to see if the diifference is all in the ISI number.

 

[EVELYN]

Jim
The protime does give both the INR and PT, which is very nice. I don't know about the Coaguchek.....Marty? do you know the answer to that? If not, I'll let you know next Friday when we check both machines with the cardio's coaguchek.

Ev

 

[Ross]

I know the Coaguchek at my Coumadin Clinic gives both.

 

[Marty]

INR and time in seconds

INR and time in seconds

Yes the Coaguchek does give the prothtrombin time in seconds
and the INR. I personally like to see both.

 

[Blanche]

This INR stuff is complicated

This INR stuff is complicated

JimChicago:
Thank heavens I share my life with an engineer who helps me understand things that have exponents. I question your calculations because you have used the INR in the equation when it is the result of the equation. There is NOTHING you can do to an INR of 2.9 to get it to read anything other than 2.9. You can not get an INR of 2.9 to read 5.0. I thinkyou missed a piece of the original equation in the transposition. Please let me explain my thinking. I've been wrong before, but the engineer is never wrong. (Smiles)

You are correct. The World Health Organization developed the International Normalized Ratio (INR), a simple equation that "standardized prothrombin time reporting so that results could be uniform across different labratories. Prior to that prothrombin time(PT) results were reported in the number of seconds that it took a sample to clot. That caused a problem because the reagents used had different sensitivity levels(expressed as ISI=International Sensitivity Index, which is explained by Evelyn in a prior post on this thread.) So, for example, if you had a reagent with the highest sensitivity of ISI= 1.0, your p/t would be reported as 39.2 seconds. However, if the reagent was a bit less sensitive, ISI=1.6, the p/t would be reported as 25.0 seconds that it took your sample to coagulate. (with an ISI=2.0, the p/t would be 21.3 and with an ISI of 2.4, your p/t would be 19.0.) So, you see, the same sample of blood could yield a p/t result of 39.2, 25.0, 21.3, or 19.0. Since different labs uses different reagents with different sensitivities, and the sensitivities changed when new batches of reagents were used, it sure was difficult to deal with the results of a prothrombin time test result that was expressed as PT. The chance of error was enormous!!!! BY THE WAY....the INR in all four examples above is 3.0. (data from ProTimeMicrocoagulation System Operator's Manual, p.36).

So, the result of all of this is that the INR should be the same with the ProTime with an INS of 1.0 or the Coagucheck with and ISI of 2.0, or any other instrument or lab test of with any ISI. Thus, the World Health Organization's International Normalized Ratio provides the same INR, regardless of the ISI...

You said, " if 2.9 (INR) is based on an INS of 1-then to get it to read 5.0(INR) instead would mean an ISI of 1.5 (since the ISI number is the exponent in the INR equation. If the 2.9 is based on an ISI of 1 when 2.9 is raised by an ISI of 2 it would be 2.9 times 2.9 =8.41." Where is the PT in this equation, which changes when the ISI changes?

Regardless how one manipulates the data, there is no way to change the INR of a prothrombin test. INR is a ratio that takes into consideration the coagulation time in seconds(PT) and the sensitivity of the reagent (ISI) and gives a result that remains constant with the same blood sample regardless of ISI.

Kind regards,
Blanche

 

[Guest]

The pro(thrombin) time is the time in seconds that it takes for the blood to clot in the test.

The materials used in the test vary. Even the strips from the same manufacturer can vary. The pro time is dependent upon how sensitive the materials are.

To overcome this problem the ISI (a sensitivity index) was devised. The INR as explained in a previous post is a relationship between how long it took the blood to clot and how sensitive the materials are.

So now when you you use different labs or different batches of strips from the same manufacturer the result is expressed as the INR, so everyone is talking about the same thing.

Sort of ---

Because of the variation and the mathematical relationship, the less sensitive the materials are (the higher the ISI number) the less accurate the number when you get farther and farther from the therapeutic range.

Actually the ISI of 1.0 is ideal. An ISI of 2.0 which is what CoaguChek uses means that the farther away from the range of 2.0 to 3.5 you get, the less accurate the number.

The problem with Evelyn's machine is not the ISI but something else that is malfunctioning. I would advise against changing the ISI.

As far as what happens to an individual, there is very little difference between an INR of 2.9 and one of 5.0. I rarely hold a dose for an INR of 5.0 or below. I would simply lower the dose by about 15% and test again in about one week. For the INR of 2.9, I would test again in one month.

I see INRs in the 5 range every day and very seldom do they cause anything except an occasional minor bloody nose. Admissions to the hospital for INRs of 5 are so rare that I can't remember when I last saw one. Even going to the Emergency Room for something that happened because of an INR of 5 is unusual.

A 5 indicates that it is time to do something, but that something is not getting excited. If it was, I wouldn't have anyone left to test.

 

[JimChicago]

Re: This INR stuff is complicated

Re: This INR stuff is complicated

JimChicago:

You said, " if 2.9 (INR) is based on an INS of 1-then to get it to read 5.0(INR) instead would mean an ISI of 1.5 (since the ISI number is the exponent in the INR equation. If the 2.9 is based on an ISI of 1 when 2.9 is raised by an ISI of 2 it would be 2.9 times 2.9 =8.41." Where is the PT in this equation, which changes when the ISI changes?

Regardless how one manipulates the data, there is no way to change the INR of a prothrombin test. INR is a ratio that takes into consideration the coagulation time in seconds(PT) and the sensitivity of the reagent (ISI) and gives a result that remains constant with the same blood sample regardless of ISI.

Kind regards,
Blanche

Blanche - Thanks for correcting me - my original calculation may have been in error- also I guess I'm assuming both machines use the same "average (mean) pt time (seconds)" as part of the formula - here is what I found on the net regarding the inr calcualtion:

From:
http://www.rcpa.edu.au/pathman/internat.htm
>>>>
Method: The result for the prothrombin time is expressed as a ratio (clotting time for patient plasma divided by time for control plasma); a correction factor (International Sensitivity Index) is applied to the prothrombin ratio (as the sensitivity of commercial thromboplastin reagents is variable) and the result issued as an INR.
>>>>>

From:
http://www.enw.org/Research-INR.htm
>>>>>
The manufacturers assign an ISI to each batch of reagent after comparing each batch to a "working reference" reagent preparation. This "working reference" has been calibrated against internationally accepted standard reference preparations which have an ISI value of 1.0 (Ortel, 1995). By definition, the more sensitive thromboplastin have an ISI of less than 1.0 and the less sensitive are greater than 1.0. The ISI value is critical for calculation of the INR, because the ISI value is the exponent in the formula. Consequently, small errors in the ISI assignment may affect the calculated INR substantially (Florell & Rodgers, 1996).
>>>>


From:
http://www.itxm.org/TMU1995/tmu6-95.htm
>>>>>
The INR is defined as the ratio of a patient PT compared to the mean PT or normal donors raised to the power of the ISI or:

INR = (patient PT/Mean Normal PT)^ISI
>>>>>

From:
http://www.hometestprogram.com/MWM115.pdf
>>>>>
The INR uses the ratio of the patient PT to the local mean normal
PT and raises that ratio to the power of the ISI (International Sensitivity Index) of the thromboplastin
reagent. Reagents with higher ISI values are less sensitive than those with low ISIs. Now the INR
results are compared when performing a comparison of two PT systems, not the PT seconds.
>>>>>


From:
http://www.coumadin-online.com/indication1.htm
>>>>
The INR can be calculated as:

INR = (observed PT ratio) ^ ISI

where the ISI (International Sensitivity Index) is the correction factor in the >>>>

Therefore in order to calculate the INR you need to know the mean pt time (average time) and the patients individual pt time.

If for example we take an average pt time of 11 seconds then with an INR of 2.9 and an ISI of 1 we have:
INR = (patient's pt time/ average pt time) ^ ISI (where ISI is the exponent)
2.9 = (patients pt time/11 seconds) raised by 1 exponent
2.9 = x/11
x = 31.9 seconds = patient's pt time

If for example we take an average pt time of 11 seconds then with an INR of 5.0 and an ISI of 2 we have:
5.0 = (patients pt time/11 seconds) raised by 2 exponent
5.0 = (x/11) ^ 2
2.236 = x/11
x = 24.6 seconds = patient's pt time

So we need to know the mean pt time, reported patient's pt time, and the ISI number to calculate the INR.

If the Protime was changed to use an ISI of 2 with a 31.9 second we would have
INR = (31.9/11) ^ 2
INR = 2.9 ^ 2
INR = 8.41

When we know the equation and all but one of the variables we can recontruct the other variable. Another fly in the ointment however is that I saw some comment that the Coaguchek may alter it's ISI based on variability of the specific batch of test strips and the test strip sets the particular ISI - if so then the Coaguchek's ISI may be 1.9 or 2.1 or something also.

I guess it would be up to each company to establish what is the correct ISI, and the ISI could possibly vary with the batch of test strips.

 

[JimChicago]

Apparently they're coming out with a new Coaguchek next year that will have an ISI of 1.0 :
http://www.coaguchek-usa.com/private/newsletters/files/august2003.pdf
(with ISI of 1 - extended room temperature storage time for testing strips)

It's also interesting that some say the Coaguchek test strips adjust the ISI setting on the Coaguchek for each batch of test strips - apparently in case of variations in the ISI.:
http://www.aacc.org/access/coagulation/qanda.shtml
>>>>
Basle, Switzerland
Marcia L. Zucker, Ph.D.
As far as I am aware, the value that changes when using the CoaguChek system is the lot specific ISI. This value is encoded on the code chip that is supplied with the test strips to ensure appropriate INR calculations.
>>>>>>