What are the key findings of this study?

Patients treated with vitamin K antagonists spending 65% (RR 2.8; 95% CI 1.9-4.3; P<0.001).

What is the clinical evidence from this study?

Study design: Cohort. Population: Venous thromboembolism (n=2304). Intervention: Vitamin K antagonists (ITTR 65%. Primary outcome: Recurrent thromboembolism (RR 2.8, 95% CI 1.9-4.3, p=< 0.001).

February 1, 2005

Individual time within target range in patients treated with vitamin K antagonists: main determinant of quality of anticoagulation and predictor of clinical outcome. a retrospective study of 2300 consecutive patients with venous thromboembolism

Q: What is the clinical evidence from this study?

Study design: Cohort. Population: Venous thromboembolism (n=2304). Intervention: Vitamin K antagonists (ITTR 65%. Primary outcome: Recurrent thromboembolism (RR 2.8, 95% CI 1.9-4.3, p=< 0.001).

Key Result

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).

Study Design

Type

Cohort (n=2,304)

Structured PICO

Does the individual time spent within INR target range (ITTR) predict clinical outcomes in patients with venous thromboembolism treated with vitamin K antagonists?

Population

2304 consecutive patients with venous thromboembolism treated with vitamin K antagonists

Intervention

Vitamin K antagonists (VKA) therapy

Comparator

Comparison across different strata of individual time spent within INR target range (ITTR): <45%, 45-65%, and >65%

Outcome

Recurrent thromboembolism and major bleedinghard clinical

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.

Main Result

Effect estimate: RR 2.8 (95% CI 1.9-4.3)

Absolute Event Rate: 16% vs 4.6%

p-value: p=< 0.001

Abstract

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.

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