Are primary care services a substitute or complement for specialty and inpatient services?

Health Services Research, Oct, 2005 by John C. Fortney, Diane E. Steffick, James F. Burgess, Jr., Matt L. Maciejewski, Laura A. Petersen

The Institute of Medicine has defined primary care as the provision of integrated, accessible health care services by clinicians who are accountable for addressing the majority of personal health care needs, developing a sustained partnership with patients, and practicing in the context of family and community (Donaldson et al. 1996). Starfield defines primary care as continuous, coordinated, and comprehensive care provided over time to populations undifferentiated by a particular disease, organ system, or gender (Starfield 1996). Both of these definitions stress the importance of focusing on (1) population-based medicine (in contrast to encounter-based medicine), (2) the continuity of care over time, and (3) the integration or coordination of care (Cooke 1995; Thompson 1996; Fontana et al. 1997; Frame, Berg, and Woolf 1997; Hall et al. 1997; Roman and Harris 1997). In an effort to practice population-based medicine and to contain health expenditures, many health maintenance organizations, the Department of Veterans Affairs (VA), and the National Health Service in the United Kingdom have all attempted to shift the locus of care from specialty and inpatient settings to the primary care setting (Manning et al. 1987; Coulter 1996; Kizer 1996).

The value of increasing access to primary care depends on whether primary care services can effectively substitute for more costly specialty and inpatient care. Most studies examining the substitution of primary care for specialty/inpatient care have used observational and cross sectional study designs. Many of these studies have correlated aggregate rates of preventable hospitalizations with aggregate measures of access to primary care services (e.g., providers per capita) across geographic areas. These studies are subject to the limitations associated with analyzing aggregate utilization rates from geographic areas (e.g., ecological fallacy, border crossing, lack of case-mix data, etc.). Findings from analyses of aggregate data have been mixed, with some studies finding a substitution effect (Bindman et al. 1995), while others do not (Goodman et al. 1997; Ricketts et al. 2001). Observational analyses of disaggregate patient-level data could provide stronger evidence for a substitution effect, but again, the empirical findings are mixed, with some finding a substitution effect (Gill and Mainous 1998; Falik et al. 2001), while others do not (Gill and Mainous 1998; Petersen et al. 1998; Gill, Mainous, and Nsereko 2000).

Quasi-experimental and experimental study designs potentially provide the strongest evidence for or against a substitution effect. In a quasi-experimental study, Rubenstein and colleagues found that hospitalizations and specialty outpatient visits at the Sepulveda VA decreased significantly after reorganizing services to increase access to primary care for veterans (Rubenstein et al. 1996). However, a multisite VA experimental study found that veterans with chronic disorders who were randomly assigned to an intensive primary care treatment intervention after hospitalization had a higher probability of being readmitted to the hospital compared with the control group (Weinberger, Oddone, and Henderson 1996). In the RAND Health Insurance Experiment, study participants were randomly assigned to receive different health benefits. Results indicated that the insurance group with free ambulatory care had a nonsignificantly higher number of inpatient admissions than enrollees facing a $1.50 deductible for ambulatory care, suggesting a trend toward a complementation effect between ambulatory and inpatient care (Phelps 1992).

From a theoretical standpoint, there are a number of possible mechanisms for the substitution of primary care for inpatient and specialty outpatient services. First, the prevention, or early detection, of illnesses that can be treated in the primary care setting, may avert the need for specialty or inpatient care (Starfield 1994; Donaldson et al. 1996). This substitution mechanism is likely to have both short-term effects (e.g., prevention of hospitalization for asthma by prevention and early treatment of exacerbations) and long-term effects (e.g., prevention of stroke by treatment of hypertension). The second possible mechanism for substitution is the prevention, or delay, of the need for specialty or inpatient care by the management of chronic health conditions (e.g., control of blood sugar to avert kidney failure in patients with diabetes mellitus) (Starfield 1994). This substitution mechanism includes routine monitoring/testing, medication management, and patient education that promotes self-management. The second substitution mechanism is likely to be more pronounced for patients with serious chronic illnesses and worse health status, although this mechanism will only be applicable for disorders that can be managed in the primary care setting effectively. The third substitution mechanism is gatekeeping (Starfield 1994). Gatekeeping policies require enrollees to obtain a referral from their primary care provider before their health plan will provide access to or pay claims for specialty visits. If primary care providers receive financial or other incentives from the health plan to maintain low referral rates, gatekeeping policies should reduce visits to specialists, although recent empirical evidence indicates that gatekeeping policies do not necessarily reduce the utilization of specialty services (Forrest et al. 2003).