Tom: I don't get any pleasure from putting down clinical labs. Many do a great job.
My first point was - the labs have less to lose if they report INR erroneously than the meters. It's true. This doesn't necessarily imply that labs always get it wrong -- only that, if they do, it probably won't do them any damage. Certainly nowhere near the damage that a faulty meter will do to the company that makes it.
My second point - labs can, and do, screw up. Over the past year, I've had at least four erroneous readings from three different labs. Perhaps they all got reagents with the wrong values. Perhaps the blood was mishandled. Perhaps, perhaps, perhaps. Whatever it was that caused the WRONG reading, the lab reading WAS wrong. Way wrong. More than 30% more than the meter WRONG. Just because a lab did the testing, you can't automatically assume that the result is correct.
Tom - like you seem to do, I used to put nearly absolute faith in the accuracy of the lab results. I've learned that this blanket confidence can sometimes be misplaced and unearned. I'm at the point, after seeing more than enough WRONG readings (more than 30% higher than the meter) from labs that a bit of skepticism is in order.
(I have to Coag-Sense meters, and when I get a funny lab reading, I test on both meters then, if I feel that it's necessary, I have my blood analyzed by a different lab).
Sure, I realize that INR measurement is inexact. I'm not looking for exact values - but, instead I look at ranges But if labs report results that are considerably out of range, I'm skeptical. I believe that I should be.