Control Tests for Home Testing

[Ericalwhite]

I too am interested in home testing. I hear alot about needing regular "control tests" to make sure the machine is accurate

I was wondering what exactly this means and what is done for these control tests?

Thanks!!

 

[Bina]

I know my pharmacist is certified to run a check every 6-12 months.
Also my doc said I should still have a vein draw at the hospital every few months as a double check, but I am very stable.

 

[Ross]

They are refering to checking your machine against one of theirs for accuracy, but the truth is, you can't do it like that. Reagents are different, equipment is different, labs are different etc.

ITC Protime and Hemosense INRatio units have controls integrated into the test cuvettes and strips. You need not worry about these being accurate. The older Coagucheck required that you run controls, they supplied at your cost, with each box of new strips and that's how you adjusted for accuracy with them. I'm not sure, but I believe the new Coaguchek units also have them integrated so you no longer have to worry about it. Basically, what your being told is no longer valid with todays new units. I'm not even going to say it was valid before.

From Hemosense:

Do I need to run external controls to check for accuracy?
There are no external controls that need to be used separately. The two on board controls on each strip are testing the integrity of the strip and sample each time a test is run.

How closely should the INRatio correlate to my current lab?
The INR value depends on many factors. For more information please see the Technical Bulletins. However as per the ISO 17593 draft titled “Clinical laboratory testing and in vitro diagnostic test systems in vitro monitoring systems for anticoagulant therapy”: Below INR 2.0, 90% of results shall be within +/- 0.5 INR, and between 2.0 to 4.0, 90% of results shall be within +/- 30%. back to top

 

[Bina]

Oooops--Correction

Oooops--Correction

Erica, I was thinking about the old model of Coaguchek.
Mine is the newer Coaguchek XS.....no pharmacy verification needed.

Each time the monitor is turned on it runs a quality check on itself.

Each batch of strips comes with a computer code chip which is inserted into the monitor. It contains calibration data and lot specific information.

Each strip itself contains a quality control function also.

Nothing else is needed.

 

[lance]

Controls Lab and monitors

Controls Lab and monitors

Hmmm got me thinking.

Like Bina, I have an XS--all controls on board and have been advised to do a vein draw simultaneously to check its accuracy every six months.

First of all I think this is comparing apples to oranges (different reagents) and if there is a significant difference between the two results who can say which method is more accurate. Veinous draws can and do sit for several hours before being processed. A patient wouldn't be advised to check the accuracy of the lab draw with a different lab draw every six months so I don't understand why home testers have to.

Wouldn't it be more accurate to find another home monitor (same brand name) and check accuracy that way? I intend to bring this subject up with my anti-coag clinic soon.

Good question and it's not my intention to hi-jack the thread.

 

[Ross]

Hmmm got me thinking.

Like Bina, I have an XS--all controls on board and have been advised to do a vein draw simultaneously to check its accuracy every six months.

First of all I think this is comparing apples to oranges (different reagents) and if there is a significant difference between the two results who can say which method is more accurate. Veinous draws can and do sit for several hours before being processed. A patient wouldn't be advised to check the accuracy of the lab draw with a different lab draw every six months so I don't understand why home testers have to.

Wouldn't it be more accurate to find another home monitor (same brand name) and check accuracy that way? I intend to bring this subject up with my anti-coag clinic soon.

Good question and it's not my intention to hi-jack the thread.

Yes it would be a good idea to compare from machine against same machine with same lot code test strips. You cannot and will not get the same INR machine vs lab for the simple reasons you cited. It will be in the ball park, but it's not going to coincide.

 

[Karlynn]

First of all I think this is comparing apples to oranges (different reagents) and if there is a significant difference between the two results who can say which method is more accurate. Veinous draws can and do sit for several hours before being processed. A patient wouldn't be advised to check the accuracy of the lab draw with a different lab draw every six months so I don't understand why home testers have to.

Exactly. This is why I cringe when I read that doctors or insurance companies are requiring patients to get a lab test every so often to verify that the machine is correct. We have one member who's doctor was requiring them to get a lab test every month to make sure the machine was correct. This all seems fine and logical - if the lab comes up with about the same number as the machine. But when they don't, the mistake is assuming the lab is the correct number.

It's kind of like making someone call a phone number on a land line to make sure their cell phone is, indeed, dialing the correct number. It's done because the person has used land lines a lot longer and feels more comfortable with them.

Now if the INR is way off on the machine, even after running a second test, it's a good idea to run a test on another machine or get a lab test done if you can't think of a reason why the INR would be so off.

 

[lance]

Lab test vs monitor test

Lab test vs monitor test

Karlynn,

That's exactly what happened yesterday. Back to back XS was within .2 of each other and on the high side so I was advised to do a lab test which sat around for a couple of hours prior to being run. One lab location does the draw and initiates the paper trail. Then the samples are batched to the lab twice a day. That's their procedure and it's carved in stone. I might add that to my knowledge I'm the only home tester they deal with. My test results did come within the allowable difference between the two methods. From what I've learned on the site lab errors are not as uncommon as they should be. It takes the lab longer to prepare the paper work than it takes me to run a test and that doesn't include driving and wait time. They're totally medieval.

When I first approached my PCP about home testing he was horrified. He would only agree to it if I tested both ways simultaneously! What's the point of having a monitor? Thankfully Ontario is coming out of the dark ages--some pharmacies have qualified personnel to administer the test on their own machines. A lot has happened here in the past two years.

Ross, hope you are feeling a bit better and coping with the heat.

For instance should a neighbour, friend, acquaintence have an XS would it really matter whether or not the strips were from the same lot number if the same brand monitor is being used. We could run our tests on each other's machine using each other's strips and compare the results. It's probably not that simple and wouldn't that be nice.

Erica,

You really started something here. Good stuff.

 

[Ross]

Well the idea of using the same batch of strips would be the reagents being the same in both strips, therefore, the results should as close as it gets. It won't make much difference between strips, but if you wanna be technical, run the same strips.

 

[ClickerTicker]

I don't run control tests, although the blurb for my Coaguchek S says I should. Mostly it's because I'm too mean to buy the control ampules. The strips for my CoaguChek are "free" under our National Health Service, but I'd have to pay for the controls.
I've settled on having a venous draw and lab test at about 6 month intervals (they're also free here) to check for accuracy. The results tend to be pretty close to my own.