title: Trends in physician referrals in the United States, 1999-2009.
abstract: BACKGROUND
  Physician referrals play a central role in ambulatory care in the United States; however, little is known about national trends in physician referrals over time. The objective of this study was to assess changes in the annual rate of referrals to other physicians from physician office visits in the United States from 1999 to 2009.
  
  
  METHODS
  We analyzed nationally representative cross-sections of ambulatory patient visits in the United States, using a sample of 845 243 visits from the National Ambulatory Medical Care Survey and National Hospital Ambulatory Medical Care Survey from 1993 to 2009, focusing on the decade from 1999 to 2009. The main outcome measures were survey-weighted estimates of the total number and percentage of visits resulting in a referral to another physician across several patient and physician characteristics.
  
  
  RESULTS
  From 1999 to 2009, the probability that an ambulatory visit to a physician resulted in a referral to another physician increased from 4.8% to 9.3% (P < .001), a 94% increase. The absolute number of visits resulting in a physician referral increased 159% nationally during this time, from 41 million to 105 million. This trend was consistent across all subgroups examined, except for slower growth among physicians with ownership stakes in their practice (P = .02) or those with the majority of income from managed care contracts (P = .007). Changes in referral rates varied according to the principal symptoms accounting for patients' visits, with significant increases noted for visits to primary care physicians from patients with cardiovascular, gastrointestinal, orthopedic, dermatologic, and ear/nose/throat symptoms.
  
  
  CONCLUSIONS
  The percentage and absolute number of ambulatory visits resulting in a referral in the United States grew substantially from 1999 to 2009. More research is necessary to understand the contribution of rising referral rates to costs of care.
authors.affiliation: Department of Health Care Policy, Harvard Medical School, Boston, MA 02215, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Barnett
authors.forename: Zirui
authors.initials: Z
authors.lastname: Song
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Landon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D032982:Contracts / Q000706:statistics & numerical data; D005260:Female; D019538:Health Care Surveys; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008329:Managed Care Programs / Q000706:statistics & numerical data; D006278:Medicare / Q000706:statistics & numerical data; D008875:Middle Aged; D009819:Office Visits / Q000706:statistics & numerical data / Q000639:trends; D010067:Ownership; D058007:Physicians, Primary Care / Q000706:statistics & numerical data; D012017:Referral and Consultation / Q000706:statistics & numerical data / Q000639:trends*; D013038:Specialization / Q000706:statistics & numerical data; D014481:United States; D055815:Young Adult