Venous thromboembolism (VTE), a term referring to blood clots in the veins, is a highly prevalent and far-reaching public health problem that can cause disability and death. VTE includes deep-vein thrombosis (DVT), a blood clot that typically forms in the deep veins of the leg, and pulmonary embolism (PE), a life-threatening condition that occurs when a blood clot breaks free and becomes lodged in the arteries of the lung. Blood clots can affect anyone – from the healthy to the chronically ill – in a variety of settings, including pregnant women, children, and people who are hospitalized, meaning that the burden of effective prevention, diagnosis, and treatment falls on a broad range of physicians.

The American Society of Hematology recognized the need for a comprehensive set of guidelines on the treatment of VTE to help the medical community better manage this serious condition. In partnership with the McMaster University GRADE Centre, it brought together more than 100 experts including haematologists, other clinicians, guideline development specialists, and patient representatives to tackle this challenge. Today, ASH announced the results of their collective efforts – the 2018 ASH Clinical Practice Guidelines on Venous Thromboembolism – in a press event timed to the publication of the first six chapters in the Society’s peer-reviewed journal Blood Advances. Four more chapters are in development.

The 2018 ASH guidelines were developed using the state-of-the-art methodology to ensure they meet the highest standards for trustworthiness and transparency. The panels were explicit about how recommendations were determined and open about the quality of the evidence that factored into the final decision-making process.

The 10 evidence-based clinical guidelines chapters cover VTE through a number of lenses, in areas in which there is currently uncertainty and variation in clinical practice:

1.Prophylaxis for hospitalized and non-hospitalized medical patients

Major Recommendations

  •  In medical inpatients at high bleeding risk who require prophylaxis, mechanical prophylaxis is preferred over blood-thinning medications
  • In medical inpatients at high VTE risk but acceptable bleeding risk, blood thinning medication is preferred over mechanical prophylaxis
  • In medical inpatients, when medication is used to prevent VTE, low-molecular-weight heparin is preferred over unfractionated heparin because it is only administered once a day and has fewer complications
  • In medical inpatients, when a medication is used to prevent VTE, low-molecular-weight heparin during the hospital stay is preferred over a direct oral anticoagulant administered in a hospital or after discharge
  • The use of combined modalities in medical inpatients (e.g., compression devices plus a blood thinner) is not necessary
  • Long-distance air travellers who do not have an elevated risk of thrombosis do not need to wear compression socks or take a blood thinner like aspirin to prevent thrombosis. Air travellers at substantially increased risk may benefit from graduated compression stockings or low-molecular-weight heparin

2.Diagnosis of VTE

Major Recommendations

  •  Unlike other venous thromboembolism, VTE diagnosis guidelines, mathematical modelling was done to predict the outcomes of various diagnostic pathways that have not been previously evaluated
  • Before considering a test, categorizing patients into the likelihood that they have venous thromboembolism,VTE will help achieve an accurate diagnosis without exposing the patient to unnecessary testing
  • A D-dimer test is the best first step to check for venous thromboembolism,VTE in patients with low pre-test probability; if results are negative, no further testing is required
  • When possible, clinicians should use a VQ scan, which exposes patients to lower radiation risk, versus a CT scan. Older individuals or those with preexisting lung disease are not ideal candidates for a VQ scan.

3.Optimal management of anticoagulation therapy

Major Recommendations

  • Most patients needing to interrupt warfarin for invasive procedures do not require a short-acting injectable anticoagulant administered during the peri-operative period, so-called bridge therapy
  • Many patients who survive major bleeding during anticoagulant therapy should resume taking anticoagulants

4.Heparin-induced thrombocytopenia

Major Recommendations

  • Using a clinical scoring system, the 4Ts score, rather than a gestalt approach will improve the accuracy of diagnosis and patient outcomes
  • Treatment options include not only conventional agents such as argatroban, bivalirudin, and danaparoid but also newer agents such as fondaparinux and the direct oral anticoagulants

5.VTE in the context of pregnancy

Major Recommendations

  • In the majority of cases, low-molecular-weight heparin is likely to be the best approach for managing superficial thrombosis
  • For treatment of pulmonary embolism and deep-vein thrombosis with low-molecular-weight heparin, it is acceptable to do weight-based dosing instead of using regular blood tests to adjust the dose
  • A majority of pregnant women with newly diagnosed venous thromboembolism,VTE at low risk of complications can be treated as outpatients

6.Treatment of pediatric VTE

Major Recommendations

  •  Central venous line-associated clots are the most common clots in children
  • If the central venous line is not working and the child is at the end of treatment, it should most likely be removed
  • Renal vein thrombosis, the most common spontaneous venous thromboembolism,VTE in children, should all receive anticoagulation therapy

7.Treatment of deep-vein thrombosis and pulmonary embolism (anticipated in 2019)

8.VTE in patients with cancer (anticipated in 2019)

9.Thrombophilia (anticipated in 2019)

10.Prevention of VTE in surgical patients (anticipated in 2019)

“McMaster University is the birthplace of evidence-based medicine and is an international leader in guideline methodology,” said Holger Schünemann, MD, PhD, Vice-Chair, VTE Guidelines and Lead Investigator, Systematic Review and Methods Team and Chair of the Department of Health Research Methods, Evidence & Impact at McMaster University in Hamilton, Ontario. “In this partnership with ASH, we applied the advanced methodology to ensure the production of guidelines that meet the highest standards for rigour and credibility that would be useful for clinicians and would improve the quality of care received by our patients.”

The 2018 ASH guidelines are the first of a larger guideline development initiative for ASH, which includes a commitment to the timely update of existing guidelines and the development of new ones on a range of hematologic conditions.

Visit for more information about the guidelines, including key takeaways from each chapter.