Since these initial reports, there has been one study published and two studies available in preprint format that have investigated the effects of therapeutic heparin in COVID-19. The largest available study evaluating anticoagulation was an analysis of 2,773 patients with COVID-19 in the Mount Sinai Health System (29). In patients requiring invasive mechanical ventilation included in this cohort, anticoagulation was associated with an in-hospital mortality of 29.1% compared with 62.7% for patients who did not receive anticoagulation. In contrast, this study found that patients who received anticoagulation were significantly more likely to require invasive mechanical ventilation. This report was retrospective, and the rationale for anticoagulation was not directly investigated, thus making these observations difficult to interpret. In a smaller retrospective cohort study evaluating 44 patients, those who received heparin had improved coagulation parameters and normalized immunity as evidenced by increased lymphocyte counts and decreased interleukin (IL)-6 levels compared with control subjects (35). Another group observed that initiation of heparin for 27 patients infected with COVID-19 improved oxygenation; this study did not include a control group (26). Based on these limited data, clinical treatment guidelines for COVID-19 have not yet recommended the use of therapeutic heparin or other forms of therapeutic anticoagulation (25). To address this question, a total of 18 clinical trials, 9 of which are recruiting, have been registered with the National Institutes of Health (https://www.clinicaltrials.gov/; as of June 2, 2020) to investigate the utility of therapeutic anticoagulation in COVID-19.