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

Starting soon · Not applicable

Conditions studied: Bariatric Surgery, Anti-Xa Activity, VTE (Venous Thromboembolism), Obesity & Overweight

In brief

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.

Key facts

Study ID: NCT07559643
Run by: University College Dublin
People needed: 180
Starts: 2026-08-01
Expected to finish: 2026-12-01
Last updated by the study team: 2026-05-18

Who can join

Age: 18 and older. Sex: any. Healthy volunteers: not accepted.

You may qualify if…

Age ≥18 years
BMI ≥40 kg/m², or BMI ≥35 kg/m² with at least one obesity-related comorbidity (type 2 diabetes, hypertension, obstructive sleep apnoea, dyslipidaemia, or metabolic dysfunction-associated steatotic liver disease (MASLD))
Scheduled to undergo laparoscopic bariatric surgery (sleeve gastrectomy or gastric bypass) at St Vincent's University Hospital, Dublin, Ireland
Capacity to provide written informed consent

You may not qualify if…

Current therapeutic anticoagulation for any indication Known allergy or hypersensitivity to tinzaparin, enoxaparin, heparin, or any heparin-derived product, including documented heparin-induced thrombocytopaenia (HIT) Any other contraindication to LMWH therapy Severe renal impairment (eGFR <30 mL/min/1.73m²) Known haematological disorder or coagulopathy Pregnancy, breastfeeding, or planning pregnancy during the study period Active major bleeding or high bleeding risk at the discretion of the treating clinician Inability to provide written informed consent Participation in another interventional clinical study within 30 days prior to enrolment

Where it is running

St Vincent's University Hospital — Dublin, Ireland

Full record on ClinicalTrials.gov

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