Background: Fixed-dose unfractionated heparin or low molecular weight heparin is the recommended treatment for venous thromboembolism (VTE) prevention in hospitalized patients. However, its efficacy has been questioned in obese population (BMI>30 kg/m2). Results of previous studies on weight-adjusted doses of heparin for VTE prevention are contradictory. Different anticoagulant regimens are used in clinical practice but their role remains to be elucidated.

Aims: To clarify the efficacy and safety of weight-adjusted-dose heparin for VTE prevention in obese medical and surgical patients by means of a meta-analysis of relevant studies.

Methods: Pubmed, Scopus and Google scholar were searched up to December 31, 2019. Twelve studies reporting VTE occurrence, bleeding events and anti-Xa levels were included. A random-effect meta-analysis was conducted to derive odds ratios (OR) comparing fixed vs weight adjusted-doses heparins on VTE occurrence (6320/13317 patients), bleeding (5840/10906 patients), anti-Xa levels (284/294 patients). Age, BMI, female patients, medical-surgical patients, design and quality of studies were extracted for moderators and meta-regression analysis.

Results: Weight-adjusted-dose heparin administration was not associated with reduced VTE occurrence (OR 1.03, 95% C.I. 0.79 to 1.35, k=14, p=NS) or increased bleeding (OR 0.84, 95% C.I. 0.65 to 1.08, k=14, p=NS) (Figure 1) but it was associated with higher anti-Xa levels (ES 2.04, 95% C.I. 1.16 to 2.92, p< 0.0001) (Figure 2). A significant heterogeneity was present for comparison of anti-Xa levels ( I2=94%, p< 0.0001) but not for VTE occurrence or bleeding ( I2=7.6% and 12.8% respectively, both p=ns). None of the moderators explained the heterogeneity of results.

Conclusions: Although weight-adjusted doses of heparin for VTE prevention are associated with higher levels of anti-Xa levels, neither VTE occurence nor bleeding are modified in obese patients hospitalized for medical or surgical reasons. Large prospectic studies are needed to better understand the efficacy and safety of different heparin regimens on primary VTE prevention in obese patients.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/weight-adjusted-versus-fixed-dose-heparin-thromboprophylaxis-in-hospitalized-obese-patients-a-systematic-review-and-meta-analysis/