OBJECTIVE: We tested the hypothesis that the frequency with which patients present to primary care physicians with certain types of health problems is inversely related to the chances of specialty referral during an office visit.
STUDY DESIGN: Cross-sectional analysis.
POPULATION: We used a data set composed of 78,107 primary care visits from the 1989 to 1994 National Ambulatory Medical Care Surveys. The physicians completed questionnaires after office visits.
OUTCOMES MEASURED: We defined the frequency of a health problem’s presentation to primary care (practice prevalence) as the percentage of all visits made to family physicians, general internists, and general pediatricians for that particular problem. We estimated the correlation between a condition’s practice prevalence and its referral ratio (percentage of visits referred to a specialist) and used logistic regression to estimate the effect of practice prevalence on the chances of referral during a visit.
RESULTS: The practice prevalence of a condition and its referral rate had a strong inverse linear relationship (r=-0.87; P <.001). Compared with visits made for the uncommon problems, the odds of referral for those with intermediate or high practice prevalence were 0.49 (P=.004) and 0.22 (P <.001), respectively. Surgical conditions were referred more often than medical conditions, and a greater burden of comorbidities increased the odds of referral.
CONCLUSIONS: Primary care physicians are more likely to make specialty referrals for patients with uncommon problems than those with common conditions. This finding highlights the responsible judgment primary care physicians employ in recognizing the boundaries of their scope of practice. Practice prevalence is a defining feature of the primary care–specialty care interface.
Primary care physicians make specialty referrals to obtain advice for clinically uncertain diagnostic evaluations or treatment plans, to obtain a specialized service that falls outside their scope of practice, because of patient or third-party requests, or because of a combination of these reasons.1 The clinical reasons for these referral decisions include characteristics of the presenting health problem, the burden and severity of comorbidities, and patient preferences for various treatments and outcomes.
Previous research has shown that certain features ascribed to morbidities influence the likelihood of specialty referral. The type of diagnosis is the most obvious determinant. In one study,2 adults with malignancies were 5 times more likely to be referred than those with respiratory illnesses. Similarly, in the Netherlands, Van Suijlekom-Smit and colleagues3 found more than an 8-fold variation among childhood diagnosis groups in the likelihood of referral. For patients with similar diagnoses, research has found that severe variants are more likely to be referred.4-7 Specialty referral is also influenced by the array and complexity of comorbid conditions.8
The conceptual foundations of primary care provide further insight into how clinical factors may influence referral to specialty care. A defining feature of primary care is the provision of a comprehensive set of services that meets the majority of a population’s health needs.9,10 Primary care physicians develop greater experience and expertise for health problems with which they are familiar than those that occur less often. It follows that they would seek specialist assistance for uncommon health problems. However, empirical evidence for this effect is currently lacking.
Our goal was to test the hypothesis that the frequency with which a condition is seen by primary care physicians (practice prevalence) influences the likelihood of referral from primary to specialty care. We use the term practice prevalence to mean the frequency of presentation to primary care physicians and to distinguish it from the frequency of occurrence in the community. Also, we examine the impact of other clinical factors on primary care physicians’ referral decisions, including patient age, sex, comorbidities, and the medical versus surgical nature of the target condition’s management.
Methods
Data Source and Study Sample
We used the 1989 to 1994 National Ambulatory Medical Care Surveys (NAMCS) to examine referrals made to specialist physicians during visits with primary care physicians. NAMCS is a nationally representative survey of office-based physician visits in the United States. Each year, a multistage probability sample of nonfederally funded US physicians who are engaged in patient care activities (excluding radiologists, anesthesiologists, and pathologists) is selected from the master files of the American Medical Association and the American Osteopathic Association. For 1 week each selected physician completes a questionnaire for a 20% to 100% systematic sample of patient visits. Details of the survey methodology and the survey instrument are presented elsewhere.11 The distribution of patient age and sex remained consistent over the 6 years of data collection we used.12 The 1995 to 1998 surveys were not used, because information on referral was not collected. Using the 1994 and 1998 NAMCS, Forrest and Whelan13 found that primary care practice patterns did not substantively differ over time. The pooled data set contained 219,830 visits, of which 78,107 (35.5%) were with generalists (self-reported specialty designation was family/general practice, general pediatrics, or general internal medicine).