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Does intermittent pneumatic compression reduce the risk of post stroke deep vein thrombosis? The CLOTS 3 trial: statistical analysis plan

Martin Dennis1*, Peter Sandercock1, Gordon Murray2, John Forbes2 and and on behalf of The CLOTS Trials Collaboration

Author Affiliations

1 Division of Clinical Neurosciences, The University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU, UK

2 Centre for Population Health Sciences, The University of Edinburgh, College of Medicine and Veterinary Medicine, Teviot Place, Edinburgh, EH8 9AG, UK

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Trials 2013, 14:66  doi:10.1186/1745-6215-14-66

Published: 6 March 2013



Venous thromboembolism (VTE) is a common and important complication of stroke. The CLOTS 3 trial aims to determine whether, compared with best medical care, best medical care plus intermittent pneumatic compression (IPC) in immobile stroke patients reduces the risk of proximal deep vein thrombosis (DVT).


The CLOTS 3 trial is a multicenter, parallel group trial with centralized randomization (minimization) to ensure allocation concealment. The protocol has been published (Trials 2012, 13:26) and is available in full at: webcite. Between December 2008 and September 2012, 105 centers in the UK recruited 2,876 immobile stroke patients within the first 3 days of their hospital admission. Patients were allocated to best medical care or best medical care plus IPC. Ultrasonographers performed a compression Doppler ultrasound scan to detect DVT in each treatment group at 7 to 10 days and 25 to 30 days. The primary outcome cluster includes symptomatic or asymptomatic DVT in the popliteal or femoral veins detected on either scan. Patients will be followed up by postal or telephone questionnaire at 6 months from randomization to detect later symptomatic DVT and pulmonary embolism (PE), and to measure functional outcome (Oxford Handicap Scale) and quality of life (EQ-5D-3L). The ultrasonographers performing the scans are blinded to treatment allocation, whereas the patients and caregivers are not. The trial has more than 90% power to detect a 4% absolute difference (12% versus 8%) in risk of the primary outcome and includes a health economic analysis.

Follow-up will be completed in April 2013 and the results reported in May 2013. In this update, we describe the statistical analysis plan.

Trial registration


Stroke; Deep vein thrombosis; Prevention; Intermittent pneumatic compression; Statistical analysis plan