unprovoked venous thromboembolism is a risk factor for long-term recurrence. J Thromb Haemost 2005; 3: 955-61.Summary. Background and Aim: Several factors are associated with an increased risk of recurrent venous thromboembolism (VTE). The aim of the study was to investigate whether the quality of oral anticoagulation therapy (OAT) is a long-term risk factor for recurrence of VTE after OAT interruption. Methods and results: A total of 297 patients (170 males) with a recent acute unprovoked VTE episode were prospectively monitored during OAT in our anticoagulation clinic and followed up for 21 months after OAT interruption. Recurrent events were recorded in 42 subjects for 493 years of follow-up [14.1% of patients; 8.5% patient-years (pt-y)] after OAT withdrawal. The rate of recurrence was not correlated to OAT duration. Subjects experiencing recurrence after OAT interruption had spent significantly more time at markedly subtherapeutic international normalized ratio (INR) levels (<1.5) and less time within the therapeutic range (2.0-3.0 INR) during OAT. Relative risk (RR) of recurrence was significantly higher [2.77 (95% confidence interval (CI) 1.49-5.18; P ¼ 0.001) and 2.70 (95% CI 1.39-5.25; P ¼ 0.003) at univariate and multivariate analysis, respectively] in those who spent more time (upper quintile) at INR values <1.5, being especially evident in the first 90 days of OAT. RR was significantly higher at univariate [2.05 (95% CI 1.07-3.96; P ¼ 0.031)] but not at multivariate [1.98 (95% CI 0.98-4.0; P ¼ 0.056)] analysis when the entire OAT period was considered. Subjects in the upper quintile of time spent at INR values <1.5 had significantly higher D-dimer values when OAT was stopped and after 3 months. Conclusions: The amount of time that subjects with an acute unprovoked VTE event spend at near-normal INR values (<1.5) during the first 3 months of treatment is associated with higher D-dimer values measured during OAT and after its interruption and is a significant risk factor for late VTE recurrence.

SummaryThis study prospectively evaluated the relationship between activated partial thromboplastin time (aPTT) and risk of venous thromboembolism (VTE) recurrence after oral anticoagulant (OA) withdrawal in patients with a previous unprovoked VTE event. Six hundred twenty-eight patients (331 males; median age: 67 years) were followed after OA interruption (mean follow-up ¼ 22 months). Three to four weeks from OA discontinuation patients were given a complete thrombophilic work-out, including aPTT (automated aPTT). Recurrent symptomatic VTE events (objectively documented) occurred in 71/628 (11AE3%, 6AE8/100 person-years) patients. The VTE recurrence rate was 17AE5% and 7AE5% in patients with aPTT in the lower (ratio £0AE90) and in the upper (ratio >1AE05) quartiles. The recurrence risk was more than twofold higher in patients with ratio £0AE90 versus those of the reference category [Relative risk (RR): 2AE38 (95% confidence interval (CI): 1AE18-4AE78)]. As expected, the increase in recurrence risk disappeared after adjustment for factor VIII, IX and XI levels [RR: 1AE74 (95%CI: 0AE43-2AE76)]. In contrast, the risk was persistently increased in patients with a ratio £0AE90 [RR: 2AE07 (95%CI: 1AE02-4AE18)] after adjustment for age, gender and d-dimer level. The aPTT predictive value was independent of the presence of inherited thrombophilic alterations. In conclusion, abnormally short aPTT values are associated with a significantly increased risk of VTE recurrence.

The factor V Leiden mutation (FVL), associated with reduced sensitivity to activated Protein C (APC), is a risk factor for venous thromboembolism (VTE) and displays a strong interaction with oral contraceptives (OC). The aim of this study was to evaluate the risk of VTE in OC users with reduced APC sensitivity unrelated to the FVL. APC sensitivity was measured by an original aPTT-based test (without sample pre-dilution in factor V-deficient plasma) in 195 women who suffered from VTE in reproductive age and in 487 healthy women with results being expressed as normalized ratio. Subjects with currently known clinically relevant thrombophilic alterations were excluded. APC normalized ratios were stratified into quartiles. The adjusted ORs of subjects in the lower quartile (>/= 0.90) was 2.46 (95%CI: 1.02-5.95). Of the 195 patients, 89 had suffered VTE during OC. The 181 healthy women who had used OC for at least 6 months in the two year period before presentation but who had stopped OC at least 3 months before blood sampling were considered OC users. The risk of VTE in subjects using OC with APC normalized ratio in the lower quartile was increased 4.9-fold (95% CI: 1.92-12.6). In conclusion, our results showed that altered APC resistance in women not carrying the FVL significantly increased the VTE risk, albeit to a lesser extent than in women also carrying the FVL. Our data also showed that OC use in women with altered APC resistance further increased the risk of VTE in a way that exceeded the additive expectation.