Introduction Patients with the antiphospholipid syndrome on anticoagulant therapy can be monitored with the INR using Point Of Care (POC) devices. However, INR values could be falsely elevated due to antiphospholipid-antibodies using POC devices. Previous studies that have compared INR values measured with POC devices and a laboratory coagulometer in APS patients varied in the methods, which makes the interpretation of the results difficult. We have, therefore, conducted this single center study to investigate whether INR values in APS patients measured with the most commonly used POC device (CoaguChek) in the Netherlands are comparable with whole blood INR values in our laboratory in the UMC Utrecht.
Methods INR values measured by the CoaguChek and by the coagulometer in our laboratory measured with the Owren method using a rabbit brain derived thromboplastin were compared in 20 consecutive APS patients. A paired students T-test was performed to compare both means and a p value <0,05 was considered as statistically significant. Linear regression analysis was performed to express the correlation between both test methods. A Bland-Altman plot was constructed to illustrate the agreement of the POC and laboratory INR. A difference >0,5 was considered clinically significant.
Results No statistically significant difference between the INR measured with the CoaguChek and the coagulometer in our laboratory was found (p >0,05). Furthermore, an acceptable correlation was found in the linear regression analysis (r=0,893). However, in 3 patients with triple antiphospholipid antibody positivity, a clinically relevant difference in the INR was found (>0,5).
Conclusion In conclusion, the CoaguChek generates comparable results with the coagulometer in our clinic. However, in a subset of patients with triple positivity the CoaguChek show a clinical relevant difference. Therefore, results of the CoaguChek in this group of patients should be interpreted with caution.
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