Accuracy of a portable international normalized ratio monitor for patients receiving a low molecular weight heparin as a bridge pending full oral anticoagulant efficacy

Abstract

Background Point of care (POC) devices measuring the international normalized ratio (INR) are accurate for patients with stable disease, but their efficiency has not been prospectively assessed during the “bridging period” when patients are receiving a low molecular weight heparin (LMWH) on top of a vitamin K antagonist (VKA) until the target INR is reached. Methods 188 dual INR measurement using the POC (INR POC) and the laboratory (INR lab) at the same time were consecutively determined : 69 in patients receiving LMWH + VKA (bridging group) and 119 in patients receiving only a VKA (control group). INRpoc was compared to INR lab. Results Test strip failure rate was higher in the bridging group than in the control group (29% vs 4% ; p < 0,001). In successful tests, POC accuracy was not modified by LMWH administration: the correlation coefficients between POC and lab INR values for the bridging group and the control group were 0,81 and 0,87 respectively, and the relative measure of divergence (RMD = INR lab – INR poc / INR lab) was lower in the bridging group than in the control group (4 ± 7% vs 10 ± 14%; p = 0,02). Finally, clinically relevant agreement between POC and laboratory was of 90% in the bridging group and 92.1% in the control group (p = 0.6). Conclusion With the POC used (INRatio), in patients receiving LMWH when the POC gives a result, it is as accurate as in patients not receiving a LMWH.