Association of Medicare and Medicaid insurance with increasing primary care-treatable emergency department visits in the United States.

OBJECTIVES: Policymakers have increasingly focused on emergency department (ED) utilization for primary care-treatable conditions as a potentially avoidable source of rising health care costs. The objective was to determine the association of health insurance type and arrival time, as indicators of limited availability of primary care, with primary care-treatable classification of ED visits.
METHODS: This was a retrospective analysis of a nationally representative sample of 241,167 ED visits from the 1997 to 2009 National Hospital Ambulatory Medical Care Surveys (NHAMCS). Probabilities of ED visits being primary care-treatable were categorized based on the primary International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code. The association of health insurance type and arrival time was determined with the average probability of the primary diagnosis being primary care-treatable using multivariable linear regression.
RESULTS: Compared to privately insured visits, Medicaid visits had a 1.7% (95% confidence interval [CI] = 1.2% to 2.2%) and uninsured visits a 2.4% (95% CI = 1.9% to 3.0%) higher probability of primary care-treatable classification, while Medicare visits had a 1.4% (95% CI = 0.7% to 2.0%) lower probability during the overall study period. Compared to business hours, weekend visits had a 1.5% (95% CI = 1.0% to 2.0%) higher probability of being primary care-treatable during the overall study period. From 1997 to 2009, the overall adjusted probability of ED visits being primary care-treatable increased by 0.19% (95% CI = 0.10 to 0.28) per year. This probability increased at a rate of 0.52% per year for Medicare visits (95% CI = 0.38% to 0.65%), more than double that of Medicaid visits (0.25% per year, 95% CI = 0.13% to 0.37%). By contrast, there was no significant change from 1997 to 2009 in the average probability of ED visits being primary care-treatable by privately insured (0.05% per year, 95% CI = -0.07 to 0.16) or uninsured (0.00% per year, 95% CI = -0.12 to 0.13) individuals.
CONCLUSIONS: These findings add to prior work that implicates insurance type and arrival time in the variation of primary care-treatable ED visits. Although primary care-treatable classification of ED visits was most associated with uninsured or Medicaid visits, this classification increased most rapidly among Medicare visits during the study period.