ORIGINAL RESEARCH Effects of Comorbidity and Clustering upon Referrals in Primary Care

Objective: To examine the effect of patient characteristics and comorbidity on referrals in primary care. Methods: Cross-sectional analysis of patient encounters and referrals during a 1-year period for a primary care network of 9 clinics. The analysis adjusted for the clustering effect of physicians and clin-ics on the data. Results: 23,720 specialty referrals were generated from 251,240 patient encounters, resulting in a total referral rate of 9.4 referrals per 100 encounters. Age, gender, and certain comorbid conditions were significant predictors of referral for any given encounter. Conclusions: Patient characteristics and comorbidity are predictors of referral. Studies of primary care processes need to account for clustering of physicians and clinics in their research design. (J Am Board Fam Pract 2005;18:449–52.) In this era of rising health care costs and increasing emphasis on patient safety, surprisingly little is known about patients ’ transition from primary to specialty care. Many explanations have been offered for the documented large variations in referra