Patients treated with vitamin K antagonists spending <45% of time within INR target range had a significantly higher risk of adverse outcomes than those with >65% (RR 2.8; 95% CI 1.9-4.3; P<0.001).
Cohort (n=2,304)
Does the individual time spent within INR target range (ITTR) predict clinical outcomes in patients with venous thromboembolism treated with vitamin K antagonists?
Individual time within target range (ITTR) is a strong predictor of recurrent thromboembolism and major bleeding in VKA-treated VTE patients, and a 30-day ITTR < 37% highly predicts poor long-term anticoagulation quality.
Effect estimate: RR 2.8 (95% CI 1.9-4.3)
Absolute Event Rate: 16% vs 4.6%
p-value: p=< 0.001
The efficacy and safety of vitamin K antagonists (VKA) are related to the actual level of anticoagulation (given as the international normalized ratio, INR). It is often difficult to maintain an optimal INR over time. We assessed the clinical impact of the individual time spent within INR target range (ITTR) in 2304 consecutive patients with venous thromboembolism. Annual incidences of recurrent thromboembolism and major bleeding were 6.2% and 2.8% respectively. The relative risk (RR) of thromboembolism was 4.5 [95% confidence interval (CI) 3.1-6.6, P 5.0, compared with INR 2.0-3.0. Patients with ITTR 65% (RR 2.8, 1.9-4.3, P 65% (RR 1.2, 0.7-1.8, P = 0.54). Annual incidences of recurrent thromboembolism were 16.0%, 4.9% and 4.6% at ITTR 65% respectively. For major bleeding these were 8.7%, 2.1% and 1.9% respectively. ITTR < 37% during the first 30 treatment days was highly predictive for the total treatment time ITTR < 45% (RR 24.2, 13.5-43.1, P < 0.001). In conclusion, ITTR can be used to identify patients on VKA at risk of recurrent thromboembolism or major bleeding. Since the 30-d ITTR is highly predictive for total treatment ITTR, these patients can be identified soon after start of treatment.
Veeger et al. (2005) conducted a cohort in Venous thromboembolism (n=2,304). Vitamin K antagonists (ITTR < 45%) vs. ITTR > 65% was evaluated on Recurrent thromboembolism (RR 2.8, 95% CI 1.9-4.3, p=< 0.001). Patients treated with vitamin K antagonists spending <45% of time within INR target range had a significantly higher risk of adverse outcomes than those with >65% (RR 2.8; 95% CI 1.9-4.3; P<0.001).