The effect of dabigatran on the activated partial thromboplastin time and thrombin time as determined by the hemoclot thrombin inhibitor assay in patient plasma samples


Seeking international standardization to ensure accurate assessment of anticoagulation with dabigatran

 

According to the latest findings of Dr. Greg Hapgood, BMBS, Department of Haematology, Monash Medical Centre, Melbourne, Australia, monitoring of dabigatran requires international standardization to ensure accurate assessment of its anticoagulatory effect. The author of these data published in the Opens external link in new windowAugust 2013 issue of the journal Opens internal link in current windowThrombosis and Haemostasis warned: “In the absence of this necessity, it is difficult to provide firm clinical recommendations regarding dabigatran levels based on aPTT and TT.”

Dabigatran may be prescribed for stroke prevention in patients with non-valvular atrial fibrillation. This modern oral direct thrombin inhibitor with a half-life of 12 to 24 hours in patients with normal renal function and a predictable pharmacodynamics effect enables administration of fixed-dose regimens without the need for routine laboratory testing. In general, it is not necessary to routinely monitor the effects of this drug. However, in certain situations such as unwanted bleeding episodes during surgery, it becomes desirable to do so. This is why Hapgood and his team of researchers had a closer look at real world experience relying on aPTT and TT as screening tests for this anticoagulant.

Their main message for patients and healthcare providers was that aPTT and TT provide complementary information when relying on such screening tests for guidance during peri-procedural management and bleeding scenarios. The scientists found that among the various aPTT reagents definite differences in responsiveness to dabigatran do exist. They stressed the fact that until now, data on laboratory monitoring of dabigatran has been based on data from plasma spiked with dabigatran, while they themselves used plasma from patients receiving dabigatran to assess the correlation between plasma dabigatran levels and aPTT and TT.

The authors, assessing the responsiveness of three additional aPTT reagents to the anticoagulant effect of dabigatran, were able to demonstrate a modest correlation between aPTT and dabigatran levels which, however, was lost at higher levels above 300 ng per ml. They noted statistically significant differences in responsiveness depending on the aPTT reagent, urging that each lab has to determine its own therapeutic range for its aPTT reagent. Moreover, TT has shown to be too sensitive to quantify dabigatran levels but was useful as a screening test to confirm the absence of dabigatran. In other words, a normal or near normal TT is associated with minimal or no dabigatran.

The article, published in Thrombosis and Haemostasis, provides an understanding of the real-world effect of dabigatran on routine screening assays in patient plasma sample. Hapgood emphasized: “We demonstrated a clinically and statistically significant difference between aPTT reagents. Our findings should prompt laboratories to assess the sensitivity of their reagent to the anticoagulatory effect of dabigatran”.


References
Hapgood G, Butler J, Malan E. et al.: Opens external link in new windowThe effect of dabigatran on the activated partial thromboplastin time and thrombin time as determined by the hemoclot thrombin inhibitor assay in patient plasma samples. Thromb Haemost 2013; 110: 308-315.

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