I have been on blood thinners for years and always had to wait for lab results to know my INR. This product is part of a larger system (tester, lancets etc.) works like a blood sugar tester. I will test on my designated lab day and compare it's result against the lab result. We'll see then. NOTE THAT THIS IS NOT REPLACEMENT FOR FORMAL LAB TESTS. THEY ARE MANAGED BY PROFESSIONNALS THAT DETERMINE DOSAGES AS YOU GO. IF COAGUCHEK IS ACCURATE, IT SERVES AS AN ADDITION TO THE FORMAL LAB TESTS IN ADJUSTING INTERIM THINNER MEDICATION DOSAGES.