Abstract
BACKGROUND: The enumeration of the primary care workforce relies on potentially inaccurate specialty designations sourced from licensure registries and clinician surveys. OBJECTIVE: To use an activity-based measure of primary care to estimate the number of physicians, nurse practitioners (NPs), and physician assistants (PAs) providing primary care to Medicare beneficiaries. DESIGN: Observational study using Medicare fee-for-service (FFS) claims data. SUBJECTS: All clinicians in the US billing Medicare in 2019 and their fee-for-service Medicare patients. MAIN MEASURES: We construct three measures that together distinguish primary care from specialty clinicians: (1) presence of evaluation and management (E&M) services in a setting consistent with primary care, (2) the dispersion of clinical care across International Classification of Diseases-10 (ICD-10) chapters, and (3) the extent of provided services that are atypical of primary care (e.g., surgical procedure). We apply parameters to the measures to identify the clinicians likely providing primary care and compare the resulting classifications across provider type. KEY RESULTS: Of physicians with at least 50 Medicare beneficiaries, 19-22% provide primary care. Of medical generalists (i.e., family medicine, internal medicine) with at least 50 beneficiaries, 61-68% provide primary care. We estimate that 40-45% of NPs and 27-30% of PAs meeting the panel size threshold are primary care providers in FFS Medicare. CONCLUSIONS: Our findings suggest that based on a primary care practice style, the number of primary care physicians in FFS Medicare is likely smaller than conventional estimates. However, compared to prior estimates, the number of primary care NPs is larger and the number of PAs is similar.