The OAT Trail: The Obesity Anti-Coagulation Thromboprophylaxis Trial.
Trial statusNot yet recruiting
Trial phaseNot applicable
Trial typeInterventional
Biological sexAll
Age18+
SponsorUniversity College Dublin
About this trial
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.
Eligibility criteria
This trial does not accept healthy volunteersQualifiers
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
Disqualifiers
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
Trial design
Design model
Parallel
Treatments tested in this trial
Anti-Xa Activity Monitoring
Diagnostic testA single venous blood sample (\~5 mL, citrated tube) drawn at 4 hours (±30 minutes) after the third consecutive LMWH dose on post-operative day 2, concurrent with routine post-operative bloods. Anti-Xa activity measured using a CE-marked in vitro diagnostic assay at the SVUH Haematology Laboratory. Results are not available in real time and do not influence clinical management. Target prophylactic range: 0.2-0.4 IU/mL per ASMBS 2021 guidance.
Tinzaparin (Leo)
DrugTinzaparin sodium administered subcutaneously once daily at 50 anti-Xa IU/kg total body weight for 21 days post-operatively, commencing on post-operative day 1. Used for pharmacological VTE prophylaxis following laparoscopic bariatric surgery.
enoxaparin
DrugEnoxaparin sodium administered subcutaneously twice daily (40 mg for weight ≤150 kg; 60 mg for weight \>150 kg) for 21 days post-operatively, commencing on post-operative day 1. Used for pharmacological VTE prophylaxis following laparoscopic bariatric surgery.
Treatment groups
180 Participants
are divided into 2 treatment groupsGroup A: Weight-based TinzaparinExperimental treatment 2 interventions
Group B: Weight-stratified EnoxaparinActive comparator 2 interventions
Trial outcomes
Primary outcomes
1
Proportion of participants achieving prophylactic anti-Xa levels
Proportion of participants achieving a prophylactic anti-Xa level of 0.2-0.4 IU/mL, measured at 4 hours (±30 minutes) after the third consecutive LMWH dose on post-operative day 2, as specified by the ASMBS 2021 position statement. Measured using a CE-marked chromogenic anti-Xa assay at the SVUH Haematology Laboratory.
Time frame
Post-operative day 2 (4 hours after third LMWH dose)Secondary outcomes
1
Incidence of clinically significant bleeding events
Incidence of minor and major bleeding events within 30 days of surgery, classified according to International Society on Thrombosis and Haemostasis (ISTH) criteria.
Time frame
30 days post-operatively2
Incidence of venous thromboembolism
Incidence of confirmed VTE events including deep vein thrombosis (DVT) and/or pulmonary embolism (PE) within 30 days of surgery, diagnosed by standard clinical imaging (duplex ultrasound or CT pulmonary angiography).
Time frame
30 days post-operatively3
Proportion achieving sub-prophylactic anti-Xa levels
Proportion of participants in each arm achieving a sub-prophylactic anti-Xa level of less than 0.2 IU/mL, measured at 4 hours (±30 minutes) after the third consecutive LMWH dose on post-operative day 2.
Time frame
Post-operative day 2 (4 hours after third LMWH dose)4
Proportion achieving supra-prophylactic anti-Xa levels
Proportion of participants in each arm achieving a supra-prophylactic anti-Xa level of greater than 0.4 IU/mL, measured at 4 hours (±30 minutes) after the third consecutive LMWH dose on post-operative day 2.
Time frame
Post-operative day 2 (4 hours after third LMWH dose)Sponsors and contacts
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Source ClinicalTrials.gov
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