Meta-analysis: Therapeutic-Dose Heparin Improves 28-Day Mortality in COVID-19 Hospitalized Patients

Background: High rates of thrombotic events and systemic inflammation among COVID-19 hospitalized patients led researchers to test whether intensified anticoagulation strategies could reduce morbidity and mortality. Previous trials yielded conflicting results, partly due to varying doses of anticoagulants—prophylactic, intermediate, or therapeutic—and heterogeneous patient severity. This comprehensive investigation, conducted by the WHO Rapid Evidence Appraisal for COVID-19 Therapies (REACT) Working Group, aimed to clarify the benefits and risks of escalated anticoagulation dosing in patients hospitalized for COVID-19.

Objective: To estimate whether higher-dose anticoagulation (therapeutic or intermediate) improves 28-day all-cause mortality compared with lower-dose anticoagulation (prophylactic or intermediate), and to evaluate secondary outcomes, including progression to mechanical ventilation, thromboembolic events, and major bleeding.

Methods: This prospective meta-analysis included randomized trials comparing higher- versus lower-dose anticoagulation for hospitalized COVID-19 patients. Investigators collected trial-level summary data, focusing primarily on heparins. Dosing categories—therapeutic, intermediate, and prophylactic—were predefined. The main outcome was 28-day mortality; secondary outcomes included progression to invasive mechanical ventilation (IMV), venous or arterial thrombotic events, and major hemorrhage. Data were analyzed using a fixed-effects model, with odds ratios (ORs) pooled across trials.

Results: Overall, 22 trials (over 11 000 total participants) contributed data, primarily evaluating heparins. For therapeutic versus prophylactic-dose heparin, 28-day mortality was significantly reduced (OR, 0.77; 95% CI, 0.64–0.93), especially among patients requiring low-flow oxygen or no supplemental oxygen. Therapeutic dose reduced thromboembolic events (OR 0.48; 95% CI, 0.36-0.64) but increased major bleeding (OR 1.90; 95% CI, 1.19-3.05) compared to prophylactic dose. In contrast, when therapeutic was compared to intermediate-dose heparin, the summary OR for 28-day mortality was 1.21 (CI, 0.93–1.58), suggesting a potential trend toward higher mortality that did not reach statistical significance. Intermediate versus prophylactic-dose comparisons revealed no conclusive mortality difference (OR, 0.95; CI, 0.76–1.19). Across all higher-dose arms, thromboembolic events decreased, while the risk of major bleeding increased, underscoring the delicate risk–benefit balance. Subgroup analyses by respiratory support level, D-dimer, and baseline severity did not indicate strong interaction effects, although sample sizes were limited in more severe illness subgroups.

Conclusions: Therapeutic-dose heparin reduces 28-day mortality relative to prophylactic-dose in hospitalized patients with COVID-19, mainly among those not requiring invasive ventilation. Mortality was similar or potentially worse when therapeutic was compared to intermediate-dose. Clinicians must weigh the lower rate of thrombotic complications against the higher bleeding risk, particularly in critically ill patients.

Implications for Practice: Although higher anticoagulant dosing appears beneficial for certain hospitalized COVID-19 patients, especially those with mild to moderate respiratory compromise, individualized assessment remains key. Current guidelines broadly recommend prophylactic dosing for the critically ill and suggest considering higher doses only in carefully selected patients. Evolving viral variants and changes in standard of care further complicate direct application of these findings to present-day hospital settings.

Study Strengths and Limitations: Strengths include prospective planning, collaboration with multiple trials, and a large pooled sample. Limitations encompass heterogeneity in dose definitions, partial reliance on published data where individual-level parameters could not be fully harmonized, and potential temporal changes in COVID-19 clinical profiles. Moreover, bleeding severity beyond major hemorrhage was not universally reported, limiting robust safety assessments.

Future Research: Further studies should focus on individualized anticoagulant strategies that consider biomarkers (for example, D-dimer) and evolving treatment protocols. Investigations examining optimal timing, duration, and post-discharge management will help refine anticoagulation practices.

Reference:

The WHO Rapid Evidence Appraisal for COVID-19 Therapies (REACT) Working Group. Anticoagulation Among Patients Hospitalized for COVID-19: A Systematic Review and Prospective Meta-analysis. Annals of Internal Medicine. DOI: https://doi.org/10.7326/ANNALS-24-00800

Shappell CN, Anesi GL. Anticoagulation for COVID-19: Seeking Clarity and Finding Yet More Gray. Annals of Internal Medicine. DOI: https://doi.org/10.7326/ANNALS-24-03244