Thromboembolism Prophylaxis in Medical Inpatients: Effect on Outcomes and Costs
Published Online: June 15, 2012
Onur Baser, MS, PhD; Nishan Sengupta, PhD; Anne Dysinger, MA; and Li Wang, MA, PhD
Venous thromboembolism (VTE) is a significant medical problem, with an estimated 200,000 to 600,000 Americans developing VTE each year.1 It is estimated that more than three-fourths of hospitalized patients in the United States have at least 1 risk factor for VTE and 48% have 2 or more risk factors.2 VTE risk is lower in medical patients than in surgical patients, but still substantial (10%-20%).3 In addition, there is increasing evidence that medical patients are less likely than surgical patients to receive thromboprophylaxis, even when it is indicated or recommended.4 In the US cohort from the multinational Epidemiologic International Day for the Evaluation of Patients at Risk for Venous Thromboembolism in the Acute Hospital Care Setting (ENDORSE) study, 48% of medical patients at risk of VTE received the recommended prophylaxis, compared with 71% of at-risk surgical patients.4 Postoperative VTE has been clearly shown to increase length of hospital stay, medical costs, and mortality,5 but far less is known about the impact VTE has on medical inpatients.
The aim of this study was to analyze the effect of pharmacologic VTE prophylaxis among medical inpatients on the incidence and timing of VTE, readmission due to VTE, bleeding events, and cost of care in the 30, 90, and 180 days in the postdischarge period after the initial (index) admission.
Subjects and Databases
This was a retrospective analysis of patient-level data from the MarketScan Hospital Drug Database (HDD) and linked outpatient files from the MarketScan Commercial and Medicare Supplemental Database from Thomson Reuters for calendar years 2005 to 2007. This is a proprietary database containing the largest collection of US employer-based patient data. Inpatient, outpatient, pharmacy, and enrollment data from MarketScan, together with linked HDD data, were used in this study. Data from 172 hospitals were identifiable for linkage in both hospital and claims databases and covered a geographically diverse area and both public and private health plans. These databases capture clinical and prescription data for the full continuum of care, including physician office visits; hospital stays; retail, mail order, and specialty pharmacies; and carve-out care.
Hospital data comprised submitted claims linked to detailed service-level hospital bills for each admission. Outpatient claims data were matched to each admission using the following patient level identifiers: date of admission, date of discharge, age, gender, and principal diagnosis. Admissions not uniquely identified by this key set of variables were excluded.
The study population consisted of all patients admitted to hospital with a primary diagnosis of chronic heart failure (CHF), thromboembolic stroke, severe lung disease, acute infection, or cancer, based on the International Classification of Diseases, Ninth Revision (ICD-9) codes (see eAppendix A, available at www.ajmc.com) during calendar years 2005 to 2007. This was defined as the index hospitalization. The population was grouped into 2 cohorts: those who developed VTE during index hospitalization and those who did not. VTE during hospitalization was identified by the presence of ICD-9 codes for deep vein thrombosis (DVT; 451.1x-451.81, 451.83-
451.9x, 452.xx, 453.2-453.9x) or pulmonary embolism ([PE] 415.1x) on hospital records. In order to ensure that patients were not erroneously designated as having VTE, true VTE was defined as any VTE event for which anticoagulant therapy was prescribed within 15 days of diagnosis.6 In accordance with current privacy rule guidelines, no patient’s identity or medical records were disclosed, except in compliance with applicable law.
Patient age, gender, and comorbidity data were collected at the index hospitalization. Comorbidity information included the Charlson Comorbidity Index,7 the Elixhauser Comorbidity Index,8 and a primary or secondary diagnosis (based on ICD-9 or ICD-9-CM codes) of congestive heart failure, peripheral arterial disease, acute coronary syndromes, hyperthyroidism, obesity, diabetes, hypertension, ischemic or hemorrhagic stroke, noncentral nervous system systemic embolism, transient ischemic attack, catheter ablation, dyspepsia, or preperiod VTE (see eAppendix B). The preperiod began 180 days before the index event (date of hospital admission).
Outcomes were analyzed according to whether or not patients received any anticoagulant prophylaxis prior to VTE or true VTE diagnosis. In addition, the following prophylactic treatment groups were identified: low molecular weight heparin (LMWH) only; warfarin only; unfractionated heparin (UFH) only; fondaparinux; LMWH + warfarin; UFH + warfarin. The drug use observation period was defined as time from admission for the index hospitalization until 30 days after index hospital discharge.
All outcomes were measured from the index admission date up to 180 days postdischarge or death, whichever occurred first. These outcomes were: the number of VTE and true VTE events; time to the VTE event; length of hospital stay (calculated at patient level); the number of major or minor bleeding events using ICD-9-CM codes (see eAppendix C); the number of patients readmitted for true VTE within 30, 90, and 180 days after index hospital discharge, based on subsequent hospital admission diagnosis of true VTE, or primary or secondary diagnosis of true VTE within 1 to 2 days of subsequent hospital admission; the number of patients readmitted with major bleeding within 30, 90, and 180 days after index hospital discharge, based on subsequent hospital admission diagnosis (primary or secondary) of major bleeding, or primary or secondary diagnosis of major bleeding 1 week before or 1 week after subsequent hospital admission; discharge status (ie, home, short-term hospital stay,
transfer to other facility, miscellaneous); and all-cause healthcare costs paid by the patient and health plan. These costs were computed for medical services (inpatient stay, emergency department visits, and ambulatory care, including physician visits and other outpatient services), pharmacy dispensing, and total combined costs. Prices were adjusted using the annual medical care component of the consumer price index to reflect inflation between the year of the claim and 2007.
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