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Regarding the insertion of inferior vena cava (IVC) filters in patients with recurrent pulmonary embolism during the first 3 months after an index pulmonary embolism, those who received IVC filters and those who did not were the same age and similar in gender.1Stein PD Matta F Lawrence FR Hughes MJ Inferior vena cava filters in patients with recurrent pulmonary embolism.Am J Med. 2019; 132: 88-92Abstract Full Text Full Text PDF Scopus (7) Google Scholar Drs. Nazare and Goldstein suggest those who received IVC filters and those who did not should have been matched for a history of gastrointestinal or intracranial bleeds, chronic kidney disease, hypercoagulable states and use of antiplatelet agents. There is no evidence, however, that these variables affect mortality according to the use of IVC filters. Nazare and Goldstein suggest that it was inappropriate to use statistics such as absolute risk reduction and relative risk reduction in our article because our study was a retrospective observational cohort study. They go on to say use of these statistics infers causality. Finally, they critiqued our use of “number needed to treat”. Recommendations for statistical analyses, however, indicate, that use of relative risk and the concomitant absolute risk reduction are not restricted from use in retrospective observational cohort studies.2Sistrom CL Garvan CW Proportions, odds and risk.Radiology. 2004; 230: 12-19Crossref PubMed Scopus (111) Google Scholar, 3Meirik O. Cohort and case-control studies. https://www.gfmer.ch/Books/Reproductive…/Cohort_and_case_control_studies.html. Accessed December 4, 2018.Google Scholar Furthermore, it is recommended that relative risk and absolute risk reduction should be used together, which we did.2Sistrom CL Garvan CW Proportions, odds and risk.Radiology. 2004; 230: 12-19Crossref PubMed Scopus (111) Google Scholar We calculated the number needed to treat because it allowed a more direct comparison of the intervention effects and thus a more robust scrutiny of the treatment results. Causality in our investigation is inferred based on the analytic results showing a risk reduction for the patients receiving the filter closely following the time they were diagnosed.3Meirik O. Cohort and case-control studies. https://www.gfmer.ch/Books/Reproductive…/Cohort_and_case_control_studies.html. Accessed December 4, 2018.Google Scholar We assume that all patients in this investigation were treated with anticoagulants for at least 3 months following the index hospitalization for pulmonary embolism. We believe that this is a valid and conservative assumption. Anticoagulant therapy is the mainstay for the treatment of venous thromboembolism.4Kearon C Akl EA Duration of anticoagulant therapy for deep vein thrombosis and pulmonary embolism.Blood. 2014; 123: 1794-1801Crossref PubMed Scopus (181) Google Scholar Patients who received an IVC filter during hospitalization for the index pulmonary embolism, as may have been the case in those who had a contraindication to anticoagulants, were excluded.1Stein PD Matta F Lawrence FR Hughes MJ Inferior vena cava filters in patients with recurrent pulmonary embolism.Am J Med. 2019; 132: 88-92Abstract Full Text Full Text PDF Scopus (7) Google Scholar It is inconceivable that patients would have been discharged after a pulmonary embolism without any anticoagulants and without an IVC filter. The duration of anticoagulants that we assume, 3 months, is the shortest duration of anticoagulant treatment that is recommended. The American College of Chest Physicians recommend treatment of pulmonary embolism for 3 months, and in some instances longer, but not shorter.5Kearon C Akl EA Ornelas J Blaivas A et al.Antithrombotic therapy for VTE disease: Chest guideline and expert panel report.Chest. 2016; 149: 315-352Abstract Full Text Full Text PDF PubMed Scopus (3362) Google Scholar The recommendations of the European Society of Cardiology for the duration of anticoagulant treatment of pulmonary embolism are the same.6Torbicki A Perrier A Konstantinides S Agnelli G Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC).Eur Heart J. 2008; 29: 2276-2315Crossref PubMed Scopus (8) Google Scholar The Scientific Statement from the American Heart Association7Jaff MR McMurtry MS Archer SL et al. Management of massive and submassive pulmonary embolism, iliofemoral deep vein thrombosis, and chronic thromboembolic pulmonary hypertension: a scientific statement from the American Heart Association.Circulation. 2011; 123: 1788-1830Crossref PubMed Scopus (1585) Google Scholar refers to the American College of Chest Physicians Guidelines5Kearon C Akl EA Ornelas J Blaivas A et al.Antithrombotic therapy for VTE disease: Chest guideline and expert panel report.Chest. 2016; 149: 315-352Abstract Full Text Full Text PDF PubMed Scopus (3362) Google Scholar and to the guidelines of the European Society of Cardiology6Torbicki A Perrier A Konstantinides S Agnelli G Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC).Eur Heart J. 2008; 29: 2276-2315Crossref PubMed Scopus (8) Google Scholar for the duration of anticoagulant therapy. It takes about 3 months to complete “active treatment” of venous thromboembolism.4Kearon C Akl EA Duration of anticoagulant therapy for deep vein thrombosis and pulmonary embolism.Blood. 2014; 123: 1794-1801Crossref PubMed Scopus (181) Google Scholar Four to 6 weeks of anticoagulation is insufficient for “active treatment”.4Kearon C Akl EA Duration of anticoagulant therapy for deep vein thrombosis and pulmonary embolism.Blood. 2014; 123: 1794-1801Crossref PubMed Scopus (181) Google Scholar It would be remote that physicians in the United States would treat pulmonary embolism with anticoagulants less than 3 months, which is contrary to the recommendations of the American College of Chest Physicians, the American Heart Association and the European Society of Cardiology. Validity Issues in Recent Cohort Study Regarding Role of Inferior Vena Cava Filter in Recurrent Pulmonary EmbolismThe American Journal of MedicineVol. 132Issue 4PreviewIn their recently published retrospective cohort study, Stein et al. tackled a very important question regarding the potential role of inferior vena cava (IVC) filter placement in the treatment of recurrent pulmonary embolism.1 However, there are several important observations that raise questions about the validity of the study. Full-Text PDF