Tom - I'm not sure that I agree with your statement that the lab reading is more accurate than the meter. I've reported on recent tests that show this - even values for blood taken a short time apart, but taken at different places, gave different results.
We should take into account, too, that INR testing doesn't give an exact value - 20% variance between meter and lab is acceptable. In my experience, when labs 'get it right' their results are often slightly lower than the CoaguChek XS, and often slightly higher than the Coag-Sense. All of these are within 20% of the lab's findings.
The meter error in the XS is NOT linear - it's been reported that the error increases the higher the INR becomes. A .3 error in an INR of 2.5 may turn into a .5 (or higher) error for an INR above 4. (High INRs should be rechecked).
Body chemistry DOES affect the results of a CoaguChek XS -- certain disorders will render the meter's result inaccurate.
The Coag-Sense uses a different method of determining INR - it actually records the time that it takes for a clot to form, then divides the time by a value for the reagent.
I suspect that DodgerFan's INR as measured on the CoaguChek XS probably IS higher than the lab results. Although it's higher than the lab, it's still within the 20% range of error. I'd only worry if it gives me an INR below 2.2 or so.
I spoke to my primary (his lab gave me a 3.88) and told him that I thought the lab was wrong, because the results on my meters nearly matched each other, and the tests that I've taken every week for a month or two. (My results on my meters ranged from 2.7 to 3.0 over a period of more than one month, and were 2.7 and 3.0 a few days after my blood was drawn, when I got the lab results).
I asked, and he offered, to have the phlebotomist draw two tubes of blood the next time I was in his office, and to send it to two different labs. This approach may show how much agreement there is in the results of the two labs (on THAT day, at least). I'll also, of course, do a test on one or both of my Coag-Sense meters, and we can compare all results. (If I had a supply of CoaguChek XS strips, I'd also run a test on my XS -- but I don't have the strips and can't afford any at this time).
For me, trusting the labs is getting more and more difficult.