International Normalized Ratio Monitoring of Vitamin K Antagonist Therapy: Comparative Performance of Point-of-Care and Laboratory-Derived Testing

Abstract

The monitoring of warfarin therapy using the international normalized ratio (INR) has now moved outside the laboratory's control by use of point-of-care (POC) devices. Although this provides patients with the convenience of immediate results and clinical assessment, POC-INRs are often performed by nonlaboratory staff with little experience in quality control. The Royal College of Pathologists of Australasia Quality Assurance Program (RCPAQAP) Haematology has devised a POC-INR external quality assessment (EQA) program that is suitable for both laboratory and nonlaboratory operators (e.g., nurses) to perform INR testing with good accuracy and precision. A comparison of the performance of the POC versus the laboratory-derived INR testing over the past 8 years has shown that the variation in test results (expressed as coefficient of variation; CV) for laboratory INRs increases with more prolonged INR values, whereas CVs for the POC-INR testing were generally lower, with a reduced dependency on INR values. In our program, the CoaguChek XS (Roche, Basel, Switzerland) showed the best performance among the POC devices. A comparative assessment with other EQA providers showed agreement and disparity with our data in terms of comparative CVs obtained between the laboratory and POC-INRs. The growth of the RCPAQAP POC-INR program from 29 to 360 in the past 12 years highlights the importance of providing suitable EQA for POC-INR staff who are unfamiliar with laboratory practice. This helps maintaining consistent results, which have important implications for the therapeutic management of patients on vitamin K antagonist therapy.

ICSH guidance for INR and D‐dimer testing using point of care testing in primary care

“…EQA for INR POC test devices has been recommended 12,13 and is available to healthcare professionals for a number of POCT devices 7,11,14,15 through organisations including UK NEQAS, 14 RCPAQAP 15 and others. This usually takes the form of the service provider sending lyophilised or liquid samples to the healthcare provider, who performs the test on their device and returns the result.…”

Position Statement on in-hospital/clinic point-of-care coagulation testing for anticoagulation monitoring in Saudi Arabia

“…POC INR testing is approved for VKA monitoring and can improve the time spent in the INR therapeutic range compared with the use of standard laboratory Prothrombin time/INR [ 30 ]. POCT for INR measurement can be as precise and accurate as laboratory testing [ 16 , 31 – 35 ], and can lead to comparable VKA-dosing decisions [ 33 , 35 , 36 ]. POC devices allow more convenient and frequent monitoring of anticoagulation therapy, inherently ensuring more patient education on anticoagulation management [ 37 ].…”

“…As previously mentioned, studies report the reliability of POC INR readings in comparison to standard laboratory based method of INR [ 16 , 31 – 35 ]. In one study, the INR values by POCT method were significantly correlated to the standard laboratory method with correlation coefficient of 0.875 [ 60 ].…”

“…However, anticoagulation monitoring gaps persist in clinical practice with detrimental effects on the quality of anticoagulation [ 14 ]. Although conventional laboratory testing have a higher precision and reliability for INR (particularly higher ranges) [ 15 , 16 ], in-hospital/clinic point-of-care (POC) anticoagulation monitoring can still play an important role in patient management. POC testing (POCT) coagulometers are used in different settings for anticoagulation monitoring, such as patient self-monitoring, anticoagulation clinic POC INR as well as the rapid determination of activated clotting time in the operating room and cardiac catheterization suite [ 17 ].…”