Background: Warfarin is commonly used for management of deep vein thrombosis (DVT) and pulmonary embolism (PE), controlling therapy by means of the International Normalized Ratio (INR).
Objectives: To identify differences in INR results between patients with thromboembolic and haemorrhagic complications and controls.
Methods: Two nested case-control studies from within a controlled trial of the duration of warfarin therapy (47 thrombotic and 16 haemorrhagic complications).
Results: Patients whose thromboembolism failed to resolve during treatment or recurred during or after treatment had non-significantly lower INR levels than matched controls (geometric mean 2.2 versus 2.3, p = 0.12). Patients with haemorrhage also had not statistically significant lower INR levels than their matched controls (2.1 versus 2.3, p = 0.22). The variability of INR levels was similar in both case groups and controls. The mean percentage of INR levels in the therapeutic range 2 - 3 was almost identical in thrombotic cases and controls (56.5% versus 56.1%). Compared to the haemorrhagic group, better control was achieved in controls (61.5% versus 43.0%, p=0.01), but controls had slightly more INR values above the therapeutic range (12.1% versus 10.5%, p = 0.74) whilst haemorrhagic cases had more INR values below the therapeutic range (46.6% versus 26.4%, p = 0.03).
Conclusion: In this study, higher INR levels were not associated with haemorrhage suggesting that, for patients being treated for DVT/PE, a modest increase in the target therapeutic range could be considered.
Keywords: Deep vein thrombosis; Haemorrhage; International normalized ratio; Pulmonary embolism; Thromboembolism; Warfarin; Warfarin Control in treatment of DVT/PE.