Level of agreement between laboratory and point-of-care prothrombin time in patients after stopping or continuation of acenocoumarol anticoagulation: A comparison of diagnostic accuracy

BACKGROUND Procedures requiring optimisation of the coagulation status of patients using vitamin K antagonists are frequently postponed due to the late availability of laboratory international normalised ratio (INR) test results. A point-of-care (POC) alternative may facilitate early decision-making in peri-operative patients. OBJECTIVES To assess the level of agreement between the POC-INR and the laboratory INR in patients who continue or stop vitamin K antagonists to determine whether the POC test may be a good alternative to the laboratory INR. DESIGN Study of diagnostic accuracy. SETTING Single-centre study at Zaans Medical Centre, The Netherlands. PATIENTS Included patients were scheduled for cardioversion (these continued taking vitamin K antagonists), or a surgical procedure (these stopped taking vitamin K antagonists). MAIN OUTCOME MEASURES The level of agreement and clinical acceptability of the laboratory and POC-INR results, evaluated by Bland–Altman analysis and error grid analysis. RESULTS The surgical and cardioversion groups consisted of 47 and 46 patients, respectively. The bias in the INR in the surgical group was −0.12 ± 0.09 with limits of agreement of −0.29 to 0.05, whereas the cardioversion group showed a bias in the INR of −0.22 ± 0.36 with limits of agreement from −0.93 to 0.48. The percentage errors between methods in the surgical and cardioversion groups were 16 and 21%, respectively. Error grid analysis showed that the diagnostic accuracy of the POC prothrombin time is clinically acceptable as the difference did not lead to a different clinical decision in the surgical group with INR values less than 1.8. CONCLUSION The current study shows a good level of agreement and clinical accuracy between the laboratory and POC-INR in patients who stopped anticoagulation intake for surgery. However, in patients who continued their anticoagulation therapy, the agreement between the two methods was less accurate.

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