Precision of Test Units

[Guest]

We have had quite a few questions about how one meter compares with another and how much any of them would vary from a standard. Roche recently published this in their OnSite Newsletter Number 45 Q2 2006 page 1 and 2. Consider the source - it is from Roche the makers of CoaguChek-S. However, they are quoting from the package inserts that go with each product. This is important because the information in the package insert has to be approved by the FDA as to its authenticity.

CoaguChek-S; If the mean INR value (determined by a reference lab) is 2.6 then 95% of the test results will be between 2.34 and 2.86.

ProTime; If the mean INR value (determined by a reference lab) is 3.2 then 95% of the test results will be between 2.82 and 3.58.

INRatio; If the mean INR value (determined by a reference lab) is 3.1 then 95% of the results will be between 2.5 and 3.7.

So this is the precision data on file with the FDA.
CoaguChek-S readings vary from 0.26 INR units low to 0.26 INR units high.
ProTime readings vary from 0.38 INR units low to 0.38 INR units high.
INRatio readings vary from 0.6 units low to 0.6 units high.

We only know for sure about the INR values given above but it is probably safe to say that if your range is 2.5 to 3.5 then any reading between:
2.2 and 3.8 is acceptable for CoaguChek-S;
2.1 and 3.9 is acceptable for ProTime;
1.9 and 4.1 is acceptable INRatio.

 

[Amelia_mom]

precision of lab test?

precision of lab test?

hi Al

My daughter home test with Coaguchek XS and so far her dosing adjustment is pretty stable except when she is going through a growth spurt.

I have been testing coagucheck with the lab result and it varies from 0.3 to 0.6! On low side it's 0.2 to 0.3 but when her INR is higher it goes to 0.5, 0.6.

Then just last week her INR has been slowly droping ('cos she was growing) and my machine says 1.8 ! I rush her down to do a lab test that showed 2.66!!! I was not convinced so 3 days later I tested , we got 1.4 and the doctor called us in after I reported and lab says 1.7.

My question is how do I know the lab test is 100% correct as compared to our coaguchek. I noticed the blood sample is collected in a valve with a little anticoagulant. Won't the amt of blood drawn or the time the valve sits in the lab before it is process affect the INR result?


cheers

 

[Guest]

A man with one watch always knows what time it is. A man with two watches never knows what time it is. The same with the person with two INR testers.

To save yourself a lot of trouble, just use the home testing unit. If you test once per week and never make adjustments up or down by more than 15% you should have no problem.

As you have now discovered, racing to the lab solved nothing and no harm was done by testing again one week later. Anticoagulation testing is not rocket science. Well maybe it is. Look at the space shuttle launch last week - even the rocket scientists couldn't agree on whether the foam popping off the fuel tank was important or not.