Correlation between PT and INR, lab vs home

[KLS39]

Previously I shared that my at home CoagSense showed an INR of 2.0 and at the lab my INR was a 2.5. I'm not concerned because the lab number is higher and both numbers are in range. Today when testing at home my INR was 1.8. It was lower than I expected but what caught my eye was that the PT in seconds was 21.8. I looked back at my lab numbers and a PT of that number would have given me around a 2.3 -2.4 at the lab. That is based on looking at my lab history over the last 4 visits. Would this have to do with different reagents? I'm guessing this is why I have that discrepancy between home and lab??

 

[pellicle]

i have never used a coagsense but I understand it has a calibration system of fluids to apply.
Have you done that recently?

The PT in seconds is a meaningless figure without knowledge of the reagent used. This is why we ceased using PT and moved to INR

 

[KLS39]

i have never used a coagsense but I understand it has a calibration system of fluids to apply.
Have you done that recently?

I did ask someone at the company that provided me with the machine and he said this calibration was done before I got the machine in November. I am going to start recording the PT in my book along with the INR and see what it looks like.

 

[pellicle]

I did ask someone at the company that provided me with the machine and he said this calibration was done before I got the machine in November. I am going to start recording the PT in my book along with the INR and see what it looks like.

Well I was just talking with a member here and he said something about the high low calibration liquids.

His machine is now a full INR point away from the lab.

 

[KLS39]

Well I was just talking with a member here and he said something about the high low calibration liquids.

His machine is now a full INR point away from the lab.

That is good information for me to have. I have to have a blood draw next week before my appointment with my cardiologist so I will have them do INR while I am there and will test at home same day.

The cardiologist talked to the company when I had the .5 discrepancy and they said in order to get a new machine I would need to test at the lab with my machine and then within 15 - 20 minutes have the lab test. I may just do that next week.

 

[pellicle]

I just did a Google and found this:

Each patient test strip kit contains 2 High and 2 Low control strips. Additional control strips can be ordered through your distributor using Catalog# 03P69-10. ​

I can only assume that means its needed ... yet when I go to the site the fcktards have made it impossible to see where that actually is with a whole bunch of collapsed questions.

Over the years here I've found two things: coag sense people love their machines, but that they seem to accept the whole series of transfer tubes and stuffing around as being somehow a benefit ... dunno.

 

[pellicle]

... so I will have them do INR while I am there and will test at home same day.

that's a good plan

 

[pellicle]

Their site is confusing and badly and busily laid out, so I downloaded the manual:

Page 5 (9 according to the PDF page)

seems pretty clear that it needs to have the high and low testing done to me ... indeed it says should be completed for each new lot of strips.

Page 7

Page 26

Sounds like an annoying and tedious system to me (as if I wanted to make my INR testing a hobby like painting model air craft).

Interestingly there have been lengthy discussions in the past (from one or two users) who are in love with their Coag Sense (CS) meanwhile the majority of Coagcheck XS users are just reporting very tight concordance with lab draws or when they are not it would almost always come down to the lab being out.

What's funny to me is that the XS is somehow designated as "professional medical users only" in the USA (implying its a tool for the professionals) meanwhile the CS is marketed at the general public.

odd.

 

[KLS39]

Their site is confusing and badly and busily laid out, so I downloaded the manual:

I did read the manual when I got the .5 discrepancy which is why I questioned the company about the control strips. I did find this on their website : Controls are run on every meter prior to the shipment from the factory. Controls are a regulatory requirement for professional offices (not self-testers). Perhaps that is why I got the answer I did. I will continue to document the discrepancies and reach back out to the company when I have all the info.

Thanks for your help.

 

[pellicle]

Controls are a regulatory requirement for professional offices (not self-testers).

right ... so my interpretation of this is: professional offices require accuracy, you don't

I will continue to document the discrepancies and reach back out to the company when I have all the info

hope you get it sorted mate

best wishes

 

[pellicle]

I am going to start recording the PT in my book along with the INR and see what it looks like.

to back up what I said before about PT being meaningless without reagent knowledge:

http://www.clinlabnavigator.com/prothrombin-time-and-inr.html

​

Because of the exponential nature of the equation for calculating the INR result, a lower ISI yields a more accurate result. The College of American Pathologists (CAP) Conference on Laboratory Monitoring of Anticoagulant Therapy held in 1998 recommended that an ISI between 0.9 and 1.7 be used, with the desired range being at the lower range of this scale. The following table illustrates the effect that the ISI can exert on the INR result.​

​

Impact of ISI on INR Results​

​

Patient PT result​	ISI​	Calculated INR result​
33.0​	1.00​	3.0​
22.9​	1.5​	3.0​
19.0​	2.00​	3.0​

​

​

INR calculations are intended to yield identical INR results when a single specimen is tested by two laboratories; one using a more sensitive thromboplastin (yielding a higher PT result) and the other using a less sensitive thromboplastin (yielding a lower PT result).​

​

It was previously believed that INR precision would be improved by using more sensitive thromboplastins (with lower ISI values). This has been shown to be incorrect​

​

 

[ETC908]

Hi KLS,
Thought I'd chime in here as I have been dealing with a similar issue and have communicated with pellicle about this as well.
Quick background-- my surgery was in November 2021. I live in the States, where we are unable to purchase our own Coagucheck device through typical means. The insurance company will purchase one for us after 90 days post-surgery. However knowing how anxious I'd be about my INR, I wanted a home device in place for right when I got home (I figured if I eventually qualified for the Coagucheck, it wouldn't hurt to have 2 devices).
So I purchased the Coagsense. Wound up being a very good purchase as my INR management from the clinic was suboptimal during the first couple of weeks, and my home machine allowed me to get my INR on target very quickly. In late November, I had a lab draw that was equal to what I was getting from my Coagsense. So that was reassuring.
Three weeks ago, the insurance company sent me the Coagucheck XS machine. First off, I find the Coagucheck easier to use, but that's beside the point. My first test on the Coagucheck was 2.9. I decided to check on the Coagsense right after that, and it was 2.2.
Over the next week or so, regular tests on both machines showed a discrepancy of 0.7, with the Coagsense being lower.
Last week I decided to test on both devices, then immediately go to the lab. The Coagucheck yielded 2.9, the Coagsense yielded 2.2. The lab draw was 2.9.
This led me to believe that the Coagsense started underestimating the INR relative to lab values somewhere between late November and early February.
I called Coagsense the other day. They were pretty helpful. He went through my technique with me, everything checked out. Long story short, they need more data. His first thought was that maybe the current strips were off (I switched to a new box of strips about a month ago). So they are sending me a new box of strips with a different lot number. The second thought was to get a couple more data points. So I'm going to test on both then go to the lab again next week to see if the Coagsense is truly the device that's off-base. It sounds like if it is, they will take the machine back and repair it.
Pellicle mentioned this calibration system they have. They have Hi control and Lo control strips, with a plasma reagent meant to test it. With this new box of strips, one of the control strips kept consistently failing. I wondered if that had something to do with it. The technician said no, that it was probably just the plasma test reagent, which is sensitive to temperature, was affected during shipment/storage. I asked repeatedly whether this could affect the accuracy of the device, and he said no. However he was a bit elusive when I asked what it was needed for...hinting that it was more of an FDA requirement and that I don't even need to use them when I get a new box of strips. Very weird.
Either way, I will be getting more data points and following up with them after I test with new strips and corroborate with the lab.

 

[KLS39]

Hi KLS,
Thought I'd chime in here as I have been dealing with a similar issue and have communicated with pellicle about this as well.
Quick background-- my surgery was in November 2021. I live in the States, where we are unable to purchase our own Coagucheck device through typical means. The insurance company will purchase one for us after 90 days post-surgery. However knowing how anxious I'd be about my INR, I wanted a home device in place for right when I got home (I figured if I eventually qualified for the Coagucheck, it wouldn't hurt to have 2 devices).
So I purchased the Coagsense. Wound up being a very good purchase as my INR management from the clinic was suboptimal during the first couple of weeks, and my home machine allowed me to get my INR on target very quickly. In late November, I had a lab draw that was equal to what I was getting from my Coagsense. So that was reassuring.
Three weeks ago, the insurance company sent me the Coagucheck XS machine. First off, I find the Coagucheck easier to use, but that's beside the point. My first test on the Coagucheck was 2.9. I decided to check on the Coagsense right after that, and it was 2.2.
Over the next week or so, regular tests on both machines showed a discrepancy of 0.7, with the Coagsense being lower.
Last week I decided to test on both devices, then immediately go to the lab. The Coagucheck yielded 2.9, the Coagsense yielded 2.2. The lab draw was 2.9.
This led me to believe that the Coagsense started underestimating the INR relative to lab values somewhere between late November and early February.
I called Coagsense the other day. They were pretty helpful. He went through my technique with me, everything checked out. Long story short, they need more data. His first thought was that maybe the current strips were off (I switched to a new box of strips about a month ago). So they are sending me a new box of strips with a different lot number. The second thought was to get a couple more data points. So I'm going to test on both then go to the lab again next week to see if the Coagsense is truly the device that's off-base. It sounds like if it is, they will take the machine back and repair it.
Pellicle mentioned this calibration system they have. They have Hi control and Lo control strips, with a plasma reagent meant to test it. With this new box of strips, one of the control strips kept consistently failing. I wondered if that had something to do with it. The technician said no, that it was probably just the plasma test reagent, which is sensitive to temperature, was affected during shipment/storage. I asked repeatedly whether this could affect the accuracy of the device, and he said no. However he was a bit elusive when I asked what it was needed for...hinting that it was more of an FDA requirement and that I don't even need to use them when I get a new box of strips. Very weird.
Either way, I will be getting more data points and following up with them after I test with new strips and corroborate with the lab.

Thank you for your reply.
Back in December when I was worried about my technique, I compared my at home with the lab, having the lab draw within an hour and not eating anything in between. There was a .2 difference with the lab being higher. I didn't think that was too bad. I checked again in January because I was increasing my dose and my INR wasn't going up. There was a .5 difference with the lab being higher. Same thing happened in February. I tried to talk to the man at the company that provides the machine but I don't think he is that knowledgeable. When he came to show me how to use the machine I asked if I had to get the sample and get it in the machine within a certain time and he told me no. I knew that was incorrect just from the research I had done on my own and from being on this forum.

Have you always gotten the hi and low control strips? I was told I didn't need them.
I will also be gathering more info, testing at home and then the lab.
If it's not too much trouble please keep me posted on your progress.
Thanks

 

[ETC908]

I have purchased 3 boxes of the Coagsense strips so far...all 3 of them came with Hi/Lo control strips. I tested the control strips on all 3 boxes. The first box worked without issue. The other two sets had issues with the control strips. Again, according to them: 1. It does not affect the accuracy of the machine and 2. I do not need to perform the control tests.
But again, it's still not clear to me why they are even there to begin with. I am awaiting the new box of strips, and will test those new strips vs. the Coagucheck vs the lab. This probably won't happen until next week, but I will be sure to provide an update.