I have had a home inr testing machine for the last 8 years of the 25 that I have been on Warfarin and recently became concerned about discrepancies in inr from the lab versus coaguchek xs. I was never told to occasionally verify my home machine with a lab test and never thought otherwise because even when I rarely got checked at my cardio, they also used a coaguchek xs, so I just assumed the machine was accurate. After reading this forum and having labs done at the dr which differed from my machine, I decided to get labs and use my machine within 30 minutes of each other to see the results. I was only able to do this 4 times before my new cardio told me to stop using the machine because my home machine was significantly higher than the lab results. My first test was a 2.5 on the coaguchek and a 2.0 from the lab. The next test was 3.3 on the machine and a 2.5 from the lab. The third test was a 3.6 on the machine and a 2.75 from the lab. The final test was a 3.8 on the machine and a 3.0 from the lab. Each of these tests varies by approximately 20% from the lab values, which I have heard is exceptable but to me this is a problem at any coaguchek measurment that is below 2.5. This potentially means that my real inr is below 2.0 which is not a good thing. This is something that has potentially been going on for nearly 8 years and could have caused serious problems. Luckily for me my old cardio had me between 2.5 and 3.5 which meant even though I was measuring on the Coaguchek, more than likely my real value was above 2.0 as long as my machines reading was 2.5. I have come too find out from a few other cardio's that I should be at an inr bewteen 2.0 and 3.0, so using my machine to regulate my inr at this new range could be a serious problem at anything below 2.5. I am not against using home inr but I would definitely suggest occasionally verify your home results with those of a labs. I also want to say that I used the strips provided by my inr testing company and used strips from different batches. I told the home monitoring company about this issue and they said they are gonna give me another machine but that was weeks ago. I love home monitoring and hopefully I will have different results with a new machine.