I [Geo] received this question from a participant on June 29, 2020: If I am at 3 for my CoaguChek reading can my hematocrit be 45 or more? Does INR affect hematocrit? I have secondary polycythemia, had an unprovoked DVT and PE and take warfarin. I tet therapeutic phlebotomies, but just question if I’m at the top of my therapeutic INR range if I can still have too many red blood cells. Thank you. [Posted with permission]
My answer: We measure anemia and polycythemia using three parameters, red blood cell count [RBC], hemoglobin [HGB] and hematocrit [HCT}. HCT is the simplest measure, it is the numerical ratio of the volume of red cells to the total volume of blood including blood plasma. Normal HCT levels are 40–54% for males and 35–49% for females. The CoaguChek instrument provides accurate linear INR results when your HCT is between 25%–55%. If over 55% it is necessary to reflex to a “laboratory-based” test. This requires blood to be collected from a vein and sent to the laboratory for the standard plasma-based assay. If your HCT is over 55%, the blood specimen requires special management by a medical laboratory scientist to ensure accuracy.
So to answer your question, while your INR result doesn’t affect your HCT result, if your HCT is over 55%, your CoaguChek INR could be inaccurate and the test should be referred to the central laboratory. By the way, your physician may have recommended one of the oral anticoagulants [blood thinners] that have been developed since 2009. Two of these are Eliquis and Xarelto, both of which require minimal laboratory testing. These have largely replaced warfarin because of their superior effectiveness and safety.