1. Division of Anaesthesia, Department of Medicine, University of Cambridge, Cambridge CB2 1TN, UK
2. Emergency Department, Cambridge University Hospitals NHS Foundation Trust, Cambridge CB2 0QQ, UK
3. Nuffield Division of Clinical Laboratory Sciences, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 9DU, UK
4. Oxford Haemophilia and Thrombosis Centre, Oxford University Hospitals NHS Foundation Trust, Oxford OX3 7LD, UK