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Comment: Analysis of the influence of dabigatran on coagulation factors and inhibitors

Sir, We read with great interest the recent publication by Tsutumi et al., regarding the effect of dabigatran on coagulation factors and inhibitors, but were surprised and troubled to note the conclusions the authors made about their results [1]. Notably, the authors indicated that ‘. . .the activities of factors II, V, VIII, and IX were decreased. . .’ and ‘. . .inhibitor against factor VIII was positive in 10 of 11 patients. . .’. Additionally the authors claim that ‘. . .each factor decreased after administration of dabigatran’. The authors concluded that dabigatran caused prolongation of the APTT, multiple factor deficiencies, and emergence of factor VIII inhibitors (which they reported became negative following cessation of dabigatran therapy). Based on these results, they advocate the use of FEIBA or recombinant factor VIIa as potential therapies in patients on dabigatran who suffer bleeding. A number of papers have been published on the effect of dabigatran on routine and specialty coagulation assays [2–4]. These published studies used normal plasma enriched with anticoagulant drug, which clearly indicates that the drug is interfering with the assay, as the samples were normal in the absence of drug. Direct oral anticoagulant agents (DOACs) have been shown to interfere with coagulation factor assays (causing spuriously low levels), coagulation factor inhibitor assays (causing factitiously positive factor inhibitors), and many other specialty coagulation assays [2–5]. As such, clinicians need to interpret results from coagulation assays with caution when patients are on DOAC therapy. We believe the authors incorrectly interpreted their laboratory data, erroneously concluding that dabigatran causes both factor deficiency and the development of factor VIII inhibitors, when these results are merely spurious and related to prolongation of global clotting tests. These data can be accurately assessed using methods that are not affected by an anticoagulant therapy (e.g. ELISA or antigenic methods), and the onus was on the authors to use such methods to verify their conclusions, especially when recommending potential therapy for the bleeding patient on dabigatran.