Background/Purpose:  Antiphospholipid Syndrome (APS) is an autoimmune disease characterized by antiphospholipid antibodies (aPL) associated with thrombosis and/or pregnancy morbidity. Although initially described in patients with systemic lupus erythematosus (SLE) it can occur in patients with no autoimmune disease. The standard treatment for thrombotic APS is anticoagulation with vitamin K antagonists. The prothrombin time (PT) and its corresponding INR (International English Normatized ratio) is the laboratory test used to target anticoagulation. Because inadequate anticoagulation therapy may be hazardous, a strict monitoring is needed. The CoaguCheck XS is a simple and prompt device that allows INR monitoring providing the result in seconds. Despite studies comparing CoaguCheck XS and PT analysis presented favorable correlation, there are scarce studies evaluating the use of CoaguCheck in APS patients. Purpose: Evaluate accuracy of CoaguCheck XS in APS patients, comparing it with standard method for plasma prothrombin time (PT). Furthermore, we analyzed other clinical and laboratorial features to check if they could interfere with CoaguCheck results. 

Methods: This is a single center cross-sectional study with 94 APS patients from a rheumatology clinic tertiary hospital included from august 2014 to march 2015. All patients fulfilled APS Sydney´s criteria and all APS associated with SLE fulfilled ACR SLE criteria. The comparison of Coagucheck XS results versus standard laboratory practice for monitoring anticoagulant therapy was evaluated using the coefficient of determination (r) followed by the Bland-Altman test. Paired T test was also applied.

 Results:  The comparison between INR values from 94 patients measured with CoaguCheck XS and the standard PT resulted in a coefficient of correlation (r) of 0.95. The mean INR (S.D.) was 2.94 (1.41) with CoaguCheck XS and 2.43 (0.86) with standard PT. Dividing the INR values in into four ranges (INR < 2, INR 2-3, INR 3-4 and INR>4) we found that INR>4 group presented a poor correlation (r=0.64) compared to the other ranges (p<0.05). Although CoaguChek XS and standard PT are highly correlated, the INR values were not equal. In general CoacuCheck shows higher values than the standard PT test, with an average of 0.42 ± 0.54. Therefore we propose a simple linear regression model in order to predict the PT standard values using values obtained from CoaguChek. The model showed a R² of 87%, indicating a good quality of forecast, for INR<2.5. None of the clinical or laboratory variables evaluated interfered with CoaguCheck results. There was no difference in testing performance in primary APS and APS associated with SLE patients. 

Conclusion: CoaguCheck XS is a simple and acceptable way of monitoring anticoagulation in APS patients presenting a good correlation with standard PT test if INR is <4. These results corfim previous reports from anticoagulated patients with no antiphospholipid syndrome.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/comparative-study-between-coagucheck-xs-versus-standard-laboratory-practice-protrombine-time-for-monitoring-anticoagulant-therapy-in-patients-with-antiphos/