Potential Overuse of Primary Thromboprophylaxis in Medical Inpatients at Low Risk of Venous Thromboembolism

Background:

Venous thromboembolism (VTE) is a common cause of morbidity and mortality in the United States. Annually, up to 1 in 120 people develop VTE, approximating the incidence of stroke. Given that hospitalization and acute medical illness increase the risk of VTE, hospital-associated VTE represents a preventable cause of morbidity and mortality. Accordingly, accreditation and regulatory agencies endorse inpatient pharmacologic VTE prophylaxis (PPX) as a quality measure. In order to raise rates of PPX prescribing, many health systems have adopted a default approach to electronic ordering, in which clinicians must "opt-out" of PPX prescription. However, this strategy may cause medical overuse and avoidable harms, which has prompted the American Society of Hematology (ASH) to recommend a risk-adapted approach to PPX. One risk model endorsed by ASH is the IMPROVE-VTE risk assessment model, which can identify patients who are at low risk for VTE and therefore may not warrant pharmacologic PPX. We therefore sought to compare the actual practice of PPX prescribing to the guideline-recommended strategy according the IMPROVE-VTE model in a large, contemporary population of medical inpatients.

Methods:

In this observational study, we used electronic health record data to identify adult, medical inpatients hospitalized on general medical and subspecialty services at Yale-New Haven Hospital from 1/1/14-12/31/18. We excluded patients who were pregnant, admitted for VTE, taking full dose anticoagulation on admission, admitted for bleeding, or had a platelet count of < 50,000/µL. For each patient, we calculated the IMPROVE-VTE score using the previously validated model weights: 3 points for a prior history of VTE; 2 points for known thrombophilia, lower limb paralysis, or active cancer; 1 point for immobilization, admission to the intensive care unit, or age ≥ 60 years. For each component other than age, we used ICD-9 and ICD-10 codes that were billed either prior to or upon admission to determine the presence of these risk factors. In order to simulate the decision to initiate PPX on hospital admission, we calculated each patient's IMPROVE-VTE score at the time of admission. In accordance with the ASH guidelines, we used an IMPROVE-VTE score of <2 to differentiate patients at low-risk of hospital-associated VTE from those at high-risk. We used inpatient medication order history data to determine receipt of pharmacologic PPX. We used χ² testing to compare the relative frequency of PPX prescribing on admission between patients at low-risk and high-risk for VTE.

Results:

We identified 135,288 medical inpatients during the study period, of whom 99,380 met inclusion criteria. The average age was 63.5 years-old (standard deviation 18 years); 51% of patients were female; 68% of patients were white. Of all the included patients, 81% received pharmacologic prophylaxis; of these patients, 78% received unfractionated heparin subcutaneously and 22% received low molecular weight heparin subcutaneously. Among all hospitalized patients, 78% had an IMPROVE-VTE score of <2 (32% had a score of 0 and 46% had a score of 1). Among these patients at low risk of hospital-associated VTE, 81% received pharmacologic PPX. Differences in prophylaxis rates between patients at low vs high risk of VTE were statistically significant (p<0.001).

Conclusion:

In this contemporary cohort of adult, medical inpatients, >80% of patients who were at low risk of hospital-associated VTE received pharmacologic PPX, representing a group in whom PPX may be unnecessary. Using a risk-adapted approach such as the IMPROVE-VTE risk assessment model, rather than default PPX ordering, may reduce medical overuse and avoidable harms.