In this study, we find a marked increase in referral rates nationally from 1999 to 2009, with the absolute number of ambulatory visits resulting in a referral more than doubling over this time period. These trends are consistent across primary care and specialist physicians as well as office-based and outpatient-department based physicians. The observed increase in referral rates does not appear to be predominantly driven by a particular patient demographic creating more demand for referrals. This evolution in care patterns may be playing a role in the rising trajectory of health care spending in the US, as referrals to specialists may lead to increased use of higher-cost services.
One potentially contradictory finding is that despite the marked increase in the referral rate, the proportion of all ambulatory visits to specialists has remained stable around 50%. This can be explained in a few ways: first, because specialists refer to PCPs,20
referrals do not always imply a new specialist visit; second, self-referral rates decreased by about 19 million, which could explain up to 30% of the total increase in referral rate and lastly, the number of ambulatory visits per 1000 persons in the US increased markedly in the 1999–2009 interval. Therefore, a possible consequence of increasing referral rates is a greater number of ambulatory visits for the average person, both in the primary care and specialist setting. It is also worth noting that only about half of referrals actually result in a completed appointment.21,22
There are several explanations for the observed increase in rates of referrals. One possibility is that care is becoming increasingly complex, thereby requiring ever more care by specialized physicians.23,24
We find some evidence to support this hypothesis in , which shows that PCPs became more likely to refer patients with certain chief complaints but not others across the interval from 1999–2002 to 2006–2009. For instance, we observe significant changes for patients with cardiovascular or dermatologic complaints, but not in areas that are more comfortably within the scope of primary care, such as general/viral symptoms. Specialist physicians saw no significant change in referral rates in these areas. Likewise, chief complaints outside the traditional spectrum of primary care, such as ocular or gynecologic/breast symptoms, had a consistently high likelihood of referral from PCPs, but had no significant change in referral rate. This suggests that some areas, such as cardiovascular and ear/nose/throat complaints, may be increasingly outside the expertise or clinical portfolio of primary care providers to manage alone. Other areas, such as gastrointestinal and orthopedic complaints, had consistently increasing referral rates for PCPs and specialists, which may reflect increasing influence of those specialties in health care markets.
A related hypothesis is that physicians are increasingly faced with more to do during the typical visit, despite no meaningful change in appointment durations in over two decades.25
Patients require more medications and more frequently have one or more chronic medical conditions.26
Moreover, screening and preventive recommendations have grown dramatically during this time period. As a result, although visit time has remained stable, physicians, and in particular PCPs, may not have enough time to address each patient issue, resulting in increased rates of referrals. Lastly, increasing numbers of specialists and availability of specialist physicians may help drive referral rates.27
This may help explain why hospital-based physicians in closer proximity to specialists in the hospital setting have referral rates close to double that of office-based physicians.
We also find that physicians who had an ownership stake in their practice had lower increases in referral rates compared to non-owner colleagues, which might reflect a financial incentive for these physicians to keep patients’ care within their practice. Supporting the potential influence of economic incentives on referral rates, physicians with greater than 50% of their income from managed care contracts also had slower growth in referral rates. Another notable result is that patients in the 3–18 year-old age group have a higher referral rate in 1999 than >65 year old patients, though this difference disappears by 2009. The >65 year old age group has a lower referral rate than younger adults in 1999 and 2009, which may reflect that these patients have generally already made relationships with providers at an earlier age for their chronic illnesses.
It is unclear whether the trends we observe reflect a change in the appropriateness of referrals over time. This is due in part to the fact that little guidance exists on how to optimally define the appropriate use of referrals. A recent review of the literature concluded that appropriateness of referrals has yet to be studied effectively.10
The complexity of referral appropriateness is compounded by the multiple roles that specialists can play in the care of a patient, ranging from consultative to procedural to co-managing a complex condition.6
This study is subject to several limitations. First, we rely on the accuracy of reporting in the NAMCS and NHAMCS instruments to measure referrals, which has been shown in one study to have high specificity but only moderate sensitivity.12
The survey question for this field also changed in 2001 for NHAMCS, from “referred to physician/clinic” to “referred to physician.” We would expect this wording change to narrow the potential range of reasons to check this category and bias our findings toward the null. Thus, the referral rates in this study are, if anything, likely underestimating national rates. Second, we have no information on why a referral has been made or to whom. This is particularly relevant for the results in and , where we rely on the assumption of a relationship between a patient’s primary reason for visit and the reason for referral. We believe that on average, it is clinically reasonable to assume that a referral has a high likelihood of relating to the primary reason that brought a patient to visit the doctor, but this may not always be the case. Another limitation is that the response rate to NAMCS has fluctuated with a gradual decline over the time period from 1999–2009. We believe that this is not likely to explain much of the change seen, especially given that the response rate for NHAMCS has been stable from 1999–2009. There is also a possibility that our findings could have been affected by changing demographic characteristics of the population. Data from the Medical Expenditure Panel Survey from 1999–2008, however, shows that the demographic composition by insurance status and income of Americans reporting that they had one or more office visits to a physician in the past year were stable (authors’ analysis, data from http://www.meps.ahrq.gov/
). Lastly, we rely on the accuracy of the sampling strategy of NAMCS and NHAMCS to produce nationally representative estimates.
In conclusion, we find that referrals in the US grew rapidly from 1999 to 2009, with potential implications for health care spending. As federal and state policymakers consider policies for reforming the health care system, developing methods to measure referral appropriateness and using these to promote appropriate referrals may be an important strategy for controlling growth in health care spending.