Association of Anti-factor Xa Activity With Venous Thromboembolism in Critically Ill Patients

Inclusion Criteria: * Age over 18 years at the time of intensive care unit admission * Admission to a participating intensive care unit within the last 24 hours * Expected discharge is later than 48 hours after enrolment Exclusion Criteria: * Therapeutic anticoagulation, defined as enoxaparin dose of at least 100 IE/kg when given twice daily or of at least 150 IE/kg when given once daily * Extracorporeal membrane oxygenation in place or planned within 48 hours of study enrolment * Planned regular administration of vitamin K antagonists, unfractionated heparin, low molecular weight heparin other than enoxaparin, thrombin inhibitors or factor X inhibitors within the observation period * Estimated life expectancy below 48 hours or comfort terminal care order in place * Previously diagnosed heparin-induced thrombocytopenia * Pre-operative admission for elective surgery * Previous enrolment in the study