The OAT Trail: The Obesity Anti-Coagulation Thromboprophylaxis Trial.

Summary

Blood clots in the legs or lungs (called venous thromboembolism or VTE) are one of the most serious complications after weight loss surgery. Most blood clots occur after patients go home from hospital, within the first 30 days after surgery. To prevent blood clots, all patients having weight loss surgery receive a daily blood-thinning injection for 21 days after their operation. Two blood-thinning injections are currently used at St Vincent's University Hospital for this purpose: enoxaparin (Clexane®) and tinzaparin (Innohep®). Both belong to a group of medicines called low molecular weight heparins (LMWHs). Patients with obesity process these medicines differently to the general population, and previous studies from our hospital have shown that fewer than 53% of patients achieve adequate blood-thinning levels with either injection when measured by a blood test called an anti-Xa level. Patients will be randomly assigned (like a coin toss) to receive either tinzaparin or enoxaparin for 21 days after their surgery. Both injections are already in routine use at this hospital. A single extra blood sample will be taken on the second day after surgery to measure the anti-Xa level, which tells us whether the injection is providing adequate protection against blood clots. This blood sample will be taken at the same time as routine post-operative blood tests so that no additional blood draws are required. The study will also look at rates of blood clots and bleeding events within 30 days of surgery, and will ask patients to complete a short questionnaire at their six-week follow-up appointment about their experience with the injection.

Timeline

Start

2026-08-01

Primary completion

2026-08-01

Completion

2026-12-01

Publications

• Background Winegar DA, Sherif B, Pate V, DeMaria EJ. Venous thromboembolism after bariatric surgery performed by Bariatric Surgery Center of Excellence Participants: analysis of the Bariatric Outcomes Longitudinal Database. Surg Obes Relat Dis. 2011 Mar-Apr;7(2):181-8. doi: 10.1016/j.soard.2010.12.008. Epub 2010 Dec 29.
• Results Chan AW, Tetzlaff JM, Gotzsche PC, Altman DG, Mann H, Berlin JA, Dickersin K, Hrobjartsson A, Schulz KF, Parulekar WR, Krleza-Jeric K, Laupacis A, Moher D. SPIRIT 2013 explanation and elaboration: guidance for protocols of clinical trials. BMJ. 2013 Jan 8;346:e7586. doi: 10.1136/bmj.e7586.
• Results World Medical Association. World Medical Association Declaration of Helsinki: ethical principles for medical research involving human subjects. JAMA. 2013 Nov 27;310(20):2191-4. doi: 10.1001/jama.2013.281053. No abstract available.
• Results Schulz KF, Altman DG, Moher D; CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMJ. 2010 Mar 23;340:c332. doi: 10.1136/bmj.c332.
• Results Atkinson MJ, Sinha A, Hass SL, Colman SS, Kumar RN, Brod M, Rowland CR. Validation of a general measure of treatment satisfaction, the Treatment Satisfaction Questionnaire for Medication (TSQM), using a national panel study of chronic disease. Health Qual Life Outcomes. 2004 Feb 26;2:12. doi: 10.1186/1477-7525-2-12.
• Results Schulz KF, Grimes DA. Allocation concealment in randomised trials: defending against deciphering. Lancet. 2002 Feb 16;359(9306):614-8. doi: 10.1016/S0140-6736(02)07750-4.
• Results Nutescu EA, Spinler SA, Wittkowsky A, Dager WE. Low-molecular-weight heparins in renal impairment and obesity: available evidence and clinical practice recommendations across medical and surgical settings. Ann Pharmacother. 2009 Jun;43(6):1064-83. doi: 10.1345/aph.1L194. Epub 2009 May 19.
• Results Aminian A, Vosburg RW, Altieri MS, Hinojosa MW, Khorgami Z; American Society for Metabolic and Bariatric Surgery Clinical Issues Committee. The American Society for Metabolic and Bariatric Surgery (ASMBS) updated position statement on perioperative venous thromboembolism prophylaxis in bariatric surgery. Surg Obes Relat Dis. 2022 Feb;18(2):165-174. doi: 10.1016/j.soard.2021.10.023. Epub 2021 Nov 10. No abstract available.
• Results Garcia DA, Baglin TP, Weitz JI, Samama MM. Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012 Feb;141(2 Suppl):e24S-e43S. doi: 10.1378/chest.11-2291.
• Results Borch KH, Braekkan SK, Mathiesen EB, Njolstad I, Wilsgaard T, Stormer J, Hansen JB. Abdominal obesity is essential for the risk of venous thromboembolism in the metabolic syndrome: the Tromso study. J Thromb Haemost. 2009 May;7(5):739-45. doi: 10.1111/j.1538-7836.2008.03234.x. Epub 2008 Nov 24.
• Results Ageno W, Becattini C, Brighton T, Selby R, Kamphuisen PW. Cardiovascular risk factors and venous thromboembolism: a meta-analysis. Circulation. 2008 Jan 1;117(1):93-102. doi: 10.1161/CIRCULATIONAHA.107.709204. Epub 2007 Dec 17.
• Results Birkmeyer NJ, Share D, Baser O, Carlin AM, Finks JF, Pesta CM, Genaw JA, Birkmeyer JD; Michigan Bariatric Surgery Collaborative. Preoperative placement of inferior vena cava filters and outcomes after gastric bypass surgery. Ann Surg. 2010 Aug;252(2):313-8. doi: 10.1097/SLA.0b013e3181e61e4f.
• Results Mechanick JI, Apovian C, Brethauer S, Timothy Garvey W, Joffe AM, Kim J, Kushner RF, Lindquist R, Pessah-Pollack R, Seger J, Urman RD, Adams S, Cleek JB, Correa R, Figaro MK, Flanders K, Grams J, Hurley DL, Kothari S, Seger MV, Still CD. Clinical Practice Guidelines for the Perioperative Nutrition, Metabolic, and Nonsurgical Support of Patients Undergoing Bariatric Procedures - 2019 Update: Cosponsored by American Association of Clinical Endocrinologists/American College of Endocrinology, The Obesity Society, American Society for Metabolic and Bariatric Surgery, Obesity Medicine Association, and American Society of Anesthesiologists. Obesity (Silver Spring). 2020 Apr;28(4):O1-O58. doi: 10.1002/oby.22719.
• Results Bray GA, Fruhbeck G, Ryan DH, Wilding JP. Management of obesity. Lancet. 2016 May 7;387(10031):1947-56. doi: 10.1016/S0140-6736(16)00271-3. Epub 2016 Feb 10.
• Results Adams TD, Davidson LE, Litwin SE, Kim J, Kolotkin RL, Nanjee MN, Gutierrez JM, Frogley SJ, Ibele AR, Brinton EA, Hopkins PN, McKinlay R, Simper SC, Hunt SC. Weight and Metabolic Outcomes 12 Years after Gastric Bypass. N Engl J Med. 2017 Sep 21;377(12):1143-1155. doi: 10.1056/NEJMoa1700459.
• Results Angrisani L, Santonicola A, Iovino P, Vitiello A, Higa K, Himpens J, Buchwald H, Scopinaro N. IFSO Worldwide Survey 2016: Primary, Endoluminal, and Revisional Procedures. Obes Surg. 2018 Dec;28(12):3783-3794. doi: 10.1007/s11695-018-3450-2.

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