Underutilization of Aspirin Persists in US Ambulatory Care for the Secondary and Primary Prevention of Cardiovascular Disease

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Despite ample evidence of aspirin underutilization, research on national trends of outpatient aspirin use by CVD risk category is limited. Using two companion national datasets on ambulatory care in the US, our study tracked changes from 1993 to 2003 in reported aspirin use by CVD risk status, distinguishing between secondary and primary prevention. Multiple reasons may account for the widespread aspirin under-utilization, one being lower priority assigned to aspirin therapy compared with other medications available for CVD risk reduction. To explore this possibility, we examined the priority given to aspirin in comparison with statins.We also examined patient and physician contributors to shortfalls in aspirin use.

Methods

The Stanford University Institutional Review Board determined that this study was exempt from ÔÇ£human subjectsÔÇØ requirements.

Data Sources

We obtained annual data 1993-2003 from the National Ambulatory Medical Care Survey (NAMCS) and the Outpatient Department component of the National Hospital Ambulatory Medical Care Survey (NHAMCS). The National Center for Health Statistics provides complete descriptions of both surveys and yearly data at http://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm These surveys, particularly NAMCS, have been validated against other data sources29,30 and utilized in past research on aspirin use for CVD risk reduction.16,25

In brief, NAMCS captured healthcare services provided by private office-based physicians, while NHAMCS captured services offered at hospital outpatient departments. The sampling universe for NAMCS was office-based, patient-care physicians in 15 specialty strata from the master files maintained by the American Medical Association and American Osteopathic Association. The sampling frame for NHAMCS included short-stay (shorter than 30 days) hospitals, or general-specialty (medical or surgical) or childrenÔÇÖs general hospitals. Both surveys utilized multistage probability sampling procedures, which enabled researchers to generate nationally representative estimates. Between 1993 and 2003, annual participation rates among physicians selected for NAMCS averaged 70%, while the participation rate of selected hospitals with outpatient departments was 90% in NHAMCS.

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