How do different aPTT reagents and thrombin time correlate with dabigatran levels measured by the Hemoclot thrombin inhibitor assay in patient plasma?
aPTT has a modest correlation with dabigatran levels but varies significantly by reagent, requiring individual laboratories to determine their own therapeutic ranges, while TT is too sensitive for quantification.
Dabigatran is an oral direct thrombin inhibitor that does not require routine laboratory monitoring. However, an assessment of its anticoagulant effect in certain clinical settings is desirable. We examined the relationship between dabigatran levels, as determined by the Hemoclot thrombin inhibitor assay (HTI), the thrombin time (TT) and the activated partial thromboplastin time (aPTT) using different reagents. We describe these parameters with the clinical outcomes of patients receiving dabigatran. Seventy-five plasma samples from 47 patients were analysed. The HTI assay was established to measure dabigatran level. aPTTs were performed using TriniCLOT aPTT S reagent (TC) and three additional aPTT reagents. From linear regression lines, we established the aPTT ranges corresponding to the therapeutic drug levels for dabigatran (90-180 ng/ml). The aPTT demonstrated a modest correlation with the dabigatran level (r= 0.80) but the correlation became less reliable at higher dabigatran levels. The therapeutic aPTT ranges for reagents were clinically and statistically different compared with our reference reagent (46-54 s (TC) vs 51-60 s (SP), 54-64 s (SS) and 61-71 s (Actin FS) (p 300 s. In conclusion, the aPTT demonstrated a modest correlation with the dabigatran level and was less responsive with supra-therapeutic levels. aPTT reagents differed in their responsiveness, suggesting individual laboratories must determine their own therapeutic range for their aPTT reagent. The TT is too sensitive to quantify dabigatran levels, but a normal TT suggests minimal or no plasma dabigatran.
Butler et al. (Tue,) studied this question.