The OAT-RCT Study: The Obesity Anti-Coagulation Thromboprophylaxis Randomised Controlled Trial.

NCT07559643 | Not Yet Recruiting

• 1 other identifier: RS26-029
• Study Type: interventional
• Target: 180
• Locations: 1 country
• Sites: 1

Brief 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.

Conditions

Bariatric Surgery; Anti-Xa Activity; Obesity & Overweight; VTE (Venous Thromboembolism)

Keywords

Anti-Xa; Metabolic Bariatric Surgery; Obesity; VTE; DVT

Outcome Measures

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.

  Post-operative day 2 (4 hours after third LMWH dose)

Secondary Outcomes (8)

• Incidence of clinically significant bleeding events

  30 days post-operatively

• Incidence of venous thromboembolism

  30 days post-operatively

• Proportion achieving sub-prophylactic anti-Xa levels

  Post-operative day 2 (4 hours after third LMWH dose)

• Proportion achieving supra-prophylactic anti-Xa levels

  Post-operative day 2 (4 hours after third LMWH dose)

• Correlation between anti-Xa level and body habitus

  Post-operative day 2

Study Arms (2)

Weight-based Tinzaparin

EXPERIMENTAL

Tinzaparin (Innohep®, LEO Pharma) administered subcutaneously once daily at a dose of 50 anti-Xa IU/kg total body weight, commencing on post-operative day 1 and continuing for 21 days. Administered via subcutaneous injection into the abdominal wall. Anti-Xa level measured at 4 hours (±30 minutes) after the third consecutive dose on post-operative day 2.

Diagnostic Test: Anti-Xa Activity Monitoring; Drug: Tinzaparin (Leo)

Weight-stratified Enoxaparin

ACTIVE COMPARATOR

Enoxaparin (Clexane®, Sanofi) administered subcutaneously twice daily, commencing on post-operative day 1 and continuing for 21 days. Dose: 40 mg twice daily for patients weighing ≤150 kg; 60 mg twice daily for patients weighing \>150 kg. Administered via subcutaneous injection into the abdominal wall. Anti-Xa level measured at 4 hours (±30 minutes) after the third consecutive dose on post-operative day 2.

Diagnostic Test: Anti-Xa Activity Monitoring; Drug: enoxaparin

Interventions

Anti-Xa Activity Monitoring DIAGNOSTIC_TEST

A 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.

Also known as: Anti-factor Xa assay; chromogenic anti-Xa assay

Weight-based Tinzaparin; Weight-stratified Enoxaparin

Tinzaparin (Leo) DRUG

Tinzaparin 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.

Also known as: Innohep

Weight-based Tinzaparin

enoxaparin DRUG

Enoxaparin 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.

Also known as: Clexane

Weight-stratified Enoxaparin

Eligibility Criteria

• Age: 18 Years+
• Sex: all
• Healthy Volunteers: No
• Age Groups: Adult (18-64), Older Adult (65+)

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

Sponsors & Collaborators

• University College Dublin: lead

Study Sites (1)

St Vincent's University Hospital

Dublin, Ireland

Location

Related Publications (16)

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MeSH Terms

Conditions

Venous Thromboembolism; Obesity; Overweight

Interventions

Tinzaparin; Enoxaparin

Condition Hierarchy (Ancestors)

Thromboembolism; Embolism and Thrombosis; Vascular Diseases; Cardiovascular Diseases; Overnutrition; Nutrition Disorders; Nutritional and Metabolic Diseases; Body Weight; Signs and Symptoms; Pathological Conditions, Signs and Symptoms

Intervention Hierarchy (Ancestors)

Heparin, Low-Molecular-Weight; Heparin; Glycosaminoglycans; Polysaccharides; Carbohydrates

Study Officials

• Helen M Heneghan, PhD, FRCSI

  University College Dublin

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Czarar A Kennedy, BMBS, MSc, MRCI

CONTACT

00353861933967; czara.kennedy@ucd.ie

Helen M Heneghan, PhD, FRCSI

CONTACT

0035312214000; helen.heneghan@ucd.ie

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: OUTCOMES ASSESSOR
• Masking Details: This is an open-label trial. The laboratory scientist performing anti-Xa analysis and the study statistician performing the primary outcome analysis are blinded to treatment allocation. The statistician will remain blinded until the primary analysis is complete.
• Purpose: BASIC SCIENCE
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Model Details: Single-centre, prospective, parallel-group, open-label, randomised controlled superiority trial comparing weight-based tinzaparin (Arm A) versus weight-stratified enoxaparin (Arm B) for 21 days post-operatively in patients undergoing laparoscopic bariatric surgery. The primary endpoint is anti-Xa activity measured on post-operative day 2.

Study Record Dates

• First Submitted: April 23, 2026
• First Posted: April 30, 2026
• Study Start: May 1, 2026
• Primary Completion (Estimated): August 1, 2026
• Study Completion (Estimated): December 1, 2026
• Last Updated: April 30, 2026

Record last verified: 2026-04

Data Sharing

• IPD Sharing: Will not share

Locations

IE (1)