Time in Therapeutic Range (TTR) Value of Patients who use Warfarin and Factors which Influence TTR

Standardization of Prothrombin Time/International Normalized Ratio (PT/INR)

The prothrombin time (PT) represents the most commonly used coagulation test in clinical laboratories. The PT is mathematically converted to the international normalized ratio (INR) for use in monitoring anticoagulant therapy with vitamin K antagonists such as warfarin in order to provide test results that are adjusted for thromboplastin and instrument used. The INR is created using two major PT 'correction factors', namely the mean normal PT (MNPT) and the international sensitivity index (ISI). Manufacturers of reagents and coagulometers have made some efforts to harmonizing INRs, for example, by tailoring reagents to specific coagulometers and provide associated ISI values. Thus, two types of ISIs may be generated, with one being a 'general' or 'generic' ISI and others being reagent/coagulometer-specific ISI values. Although these play a crucial role in improving INR results between laboratories, these laboratories reported INR values are known to still differ, even when laboratories use the same thromboplastin reagent and coagulometer. Moreover, ISI values for a specific thromboplastin can vary among different models of coagulometers from a manufacturer using the same method for clot identification. All these factors can be sources of error for INR reporting, which in turn can significantly affect patient management. In this narrative review, we provide some guidance to appropriate ISI verification/validation, which may help decrease the variability in cross laboratory reporting of INRs.

Outcomes associated with warfarin time in therapeutic range among US veterans with nonvalvular atrial fibrillation

BACKGROUND

Poor quality of warfarin control (time in therapeutic range [TTR] < 65%) can lead to increased risk of adverse events. The objective of this study was to examine the overall quality of international normalized ratio (INR) control and the association of TTR with clinical outcomes including stroke, major bleeding, and all-cause mortality among US warfarin users.

METHODS AND RESULTS

This retrospective observational cohort study utilized the US Veterans Affairs electronic medical records database (VA EMR). Patients with NVAF who newly initiated warfarin from 1 January 2005 to 31 December 2015 were grouped into two cohorts based on TTR <65% or ≥65%. TTR was computed from INR test results. Clinical outcomes assessed were stroke/systemic embolism (SE), hemorrhagic stroke, ischemic stroke, and major bleeding, defined based on hospitalization with those conditions as primary diagnosis, as well as all-cause mortality. Patients were followed from warfarin initiation to the first occurrence of an outcome or censoring. Propensity score weighted time-varying Cox regression was used to evaluate the risk of the clinical events. A total of 127,385 NVAF patients with mean TTR of 51% were included. TTR <65% was observed in 65% of patients. Mean CHA₂DS₂-VAS_C score (SD) was 2.9 (1.5) in the low TTR cohort and 2.7 (1.4) in the high TTR cohort. Patients with TTR <65% had a higher risk for any stroke/SE (HR: 1.57; 95% CI: 1.41-1.75), major bleeding (HR: 2.78; 95% CI: 2.55-3.03) and all-cause mortality (HR: 1.73; 95% CI: 1.67-1.79).

CONCLUSIONS

The observed quality of warfarin control in VA EMR suggests room for improvement given the association with elevated risk of adverse clinical outcomes.

Systematic review and network meta-analysis of the relative efficacy and safety of edoxaban versus other nonvitamin K antagonist oral anticoagulants among patients with nonvalvular atrial fibrillation and CHADS2 score ⩾ 2

Background:

The nonvitamin K antagonist oral anticoagulants pivotal clinical trials for stroke prevention in atrial fibrillation have important differences in trial designs and baseline patient characteristics.

Objective:

We sought to evaluate the relative efficacy and safety of edoxaban versus other nonvitamin K antagonist oral anticoagulants in the management of stroke prevention in atrial fibrillation by adjusting for differences in baseline stroke risk and the length of follow-up among the four phase 3 randomized controlled trials.

Methods:

We conducted a systematic literature review of randomized controlled trials evaluating the nonvitamin K antagonist oral anticoagulants for stroke prevention in atrial fibrillation and performed a network meta-analysis using data from ENGAGE AF-TIMI 48, RE-LY, ROCKET-AF, and ARISTOTLE, with warfarin as a common comparator. To adjust for between-trial differences in CHADS₂ score and length of follow-up, annualized event rates among patients with CHADS₂ score ⩾ 2 were analyzed using a mixed Poisson’s regression model.

Results:

Once-daily high-dose edoxaban was associated with significant lower major bleeding episodes compared with once-daily rivaroxaban (risk ratio, 0.76; 95% confidence interval, 0.66–0.89), twice-daily dabigatran 150 mg (risk ratio, 0.78; 95% confidence interval, 0.61–0.84), and twice-daily dabigatran 110 mg (risk ratio, 0.83; 95% confidence interval, 0.71–0.98) and similar bleeding risk compared with twice-daily apixaban (risk ratio, 1.08; 95% confidence interval, 0.91–1.28). Risk of stroke and systemic embolism was similar for the high-dose edoxaban and other nonvitamin K antagonist oral anticoagulant regimens. The low-dose edoxaban regimen was associated with a significant lower risk of major bleeding than other nonvitamin K antagonist oral anticoagulants and a significant higher risk of stroke and systemic embolism compared with apixaban and dabigatran 150 mg.

Conclusion:

Among patients with atrial fibrillation and CHADS₂ score ⩾ 2, the high-dose edoxaban regimen may offer similar efficacy to the other nonvitamin K antagonist oral anticoagulants but with a significant major bleeding benefit over rivaroxaban and dabigatran.