Applied Evidence

Primary prevention of VTE spans a spectrum

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References

Cancer increases risks of VTE and bleeding

Cancer increases VTE risk > 6-fold31; metastases, chemotherapy, and radiotherapy further increase risk. Cancer also greatly increases the risk of bleeding: Cancer patients with VTE have an annual major bleeding rate ≥ 20%.32 Guidelines do not recommend primary VTE prophylaxis for cancer, although American Society of Clinical Oncology guidelines discuss consideration of prophylaxis for select, high-risk patients,33,34 including those with multiple myeloma, metastatic gastrointestinal cancer, or metastatic brain cancer.31,34 Recent evidence (discussed in a moment) supports the use of apixaban for primary VTE prevention during chemotherapy for high-risk cancer.

The Khorana Risk Score (TABLE 435,36) for VTE was developed and validated for use in patients with solid cancer35: A score of 2 conveys nearly a 10% risk of VTE over 6 months.36 A recent study of 550 cancer patients with a Khorana score of ≥ 2—the first evidence of risk-guided primary VTE prevention in cancer—showed that primary prophylaxis with 2.5 mg of apixaban, bid, reduced the risk of VTE (NNT = 17); however, the number needed to harm (for major bleeding) was 59.37 Mortality was not changed with apixaban treatment.37

Khorana Risk Score for venous thromboembolism in patients with cancer

Primary VTE prevention in med-surg hospitalizations

The risk of VTE increases significantly during hospitalization, although not enough to justify universal prophylaxis. Recommended prevention strategies for different classes of hospitalized patients are summarized below.

In medically hospitalized patients, risk is stratified with a risk-assessment model. Medically hospitalized patients have, on average, a VTE risk of 1.2%23; 12 risk-assessment models designed to stratify risk were recently compared.38 Two models, the Caprini Score (TABLE 5)39 and the IMPROVE VTE Risk Calculator,40 were best able to identify low-risk patients (negative predictive value, > 99%).38 American Society of Hematology guidelines recommend IMPROVE VTE or the Padua Prediction Score for risk stratification.41 While the Caprini score only designates 11% of eventual VTE cases as low risk, both the IMPROVE VTE and Padua scores miss more than 35% of eventual VTE.38

Caprini Risk Score for nonorthopedic surgery

There is no prospective evidence that weight loss or control of diabetes or hypertension reduces the risk of VTE; smoking cessation does appear to reduce risk.

Because LMWH prophylaxis has been shown to reduce VTE by 40% without increasing the risk of major bleeding, using Caprini should prevent 2 VTEs for every 1000 patients, without an increase in major bleeding and with 13 additional minor bleeding events.42

Continue to: Critically ill patients

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