George received this question from an anticoagulation clinic coordinator last week: What value would you suggest to repeat a high fingerstick INR to a venous blood, >4.0, >5.0, etc. and why? Thank you. Here is the answer George provided:
“Hello, and thank you for your question. Point of care (POC) instruments provide rapid PT/INR turnaround with reasonable precision, making them indispensable tools for anticoagulation clinics. Medscape provides informative comments from Dr. Jack Ansell, founder of the Anticoagulation Forum, on the use of these instruments. The precision and linearity of conventional plasma-based “central laboratory” PT/INRs is superior to POC and the managers of most anticoagulation clinics that use POC instruments choose to reflex the assay to the lab for confirmation if there is a significant change from a patient’s previous PT/INR result or if a result is unexpectedly high. Of course, this means the patient now endures a venipuncture and is delayed an hour or two. I just returned from speaking engagements in two locations, and with your question in mind, I asked audience members, all medical lab scientists, which INR they consider to be critical, 4.0 or 5.0. In both locations the audiences were evenly divided!
I recommend you use 4.0 based on data published in Turpie AGG. New oral anticoagulants in atrial fibrillation. Eur Heart J 2008;29:155-65. Turpie shows that the risks of a serious bleed begin to rise dramatically at 4.0. However, there exist no published data that delineate the benefits and adverse outcomes of choosing 4.0 vs. 5.0 as the reflex value for POC, nor do the operators’ manuals of the various POC instruments provide a conclusion. Of course, at 4.0 you inconvenience more patients and incur greater expense, at 5.0 you risk sending home a patient with a bleeding risk. Since I’ve found no documented conclusion, I have posted your question as a “Quick Question” survey on www.fritsmafactor.com. Please watch for the survey and check the answers that it accumulates over the next few days.