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DOI: 10.1148/radiol.2452070193
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(Radiology 2007;245:517-522.)
© RSNA, 2007

Health Policy and Practice

Utilization of Diagnostic Medical Imaging: Comparison of Radiologist Referral versus Same-Specialty Referral1

G. Scott Gazelle, MD, MPH, PhD, Elkan F. Halpern, PhD, Heather S. Ryan, MSc, and Angela C. Tramontano, MPH

1 From the Institute for Technology Assessment, Massachusetts General Hospital, 101 Merrimac St, 10th Floor, Boston, MA 02114-4724 (G.S.G., E.F.H., H.S.R., A.C.T.); and Department of Health Policy and Management, Harvard School of Public Health, Boston, Mass (G.S.G.). From the 2006 RSNA Annual Meeting. Received January 29, 2007; revision requested March 15; revision received March 28; accepted April 11; final version accepted April 27. Supported in part by a grant from the American College of Radiology. Address correspondence to G.S.G.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Purpose: To retrospectively compare the frequency with which patients underwent diagnostic medical imaging procedures during episodes of outpatient medical care according to whether their physicians referred patients for imaging to themselves and/or physicians in their same specialty or to radiologists.

Materials and Methods: Institutional review board approval was not necessary for this HIPAA-compliant study. An insurance claims database from a large national employer-based health plan was obtained. Claims data from 1999–2003 were grouped into episodes of care for six conditions: cardiopulmonary disease, coronary and/or cardiac disease, extremity fracture, knee pain, intraabdominal malignancy, and stroke. For each condition, each referring physician's behavior was categorized as either "same-specialty referral" or "radiologist referral" on the basis of that physician's entire history of imaging referrals for the condition. The frequency with which patients underwent diagnostic medical imaging procedures during episodes of care was compared according to whether their physicians referred patients for imaging to themselves and/or same-specialty physicians or to radiologists. Rates were compared by using {chi}2 tests, and logistic regression was used to compare utilization rates, with patient age and number of comorbidities as covariates.

Results: For the conditions evaluated, physicians who referred patients to themselves or to other same-specialty physicians for diagnostic imaging used imaging between 1.12 and 2.29 times as often, per episode of care, as physicians who referred patients to radiologists (P < .005 for all comparisons). Adjusting for patient age and comorbidity, the likelihood of imaging was 1.196–3.228 times greater for patients cared forby same-specialty–referring physicians.

Conclusion: Same-specialty–referring physicians tend to utilize imaging more frequently than do physicians who refer their patients to radiologists. These results cannot be explained by differences in case mix (because analyses were performed within six specific conditions of interest), patient age, or comorbidity.

© RSNA, 2007


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
The use of diagnostic medical imaging has increased rapidly during the past several years, and relatively recent studies suggest that imaging by nonradiologists has increased at a faster rate than imaging by radiologists (1,2). In the face of these increases, the potential for conflicts of interest associated with self referral or with same-specialty referral to affect utilization has garnered attention (3). Results of prior studies investigating the effect of self referral on the utilization of diagnostic medical imaging have demonstrated that physicians who do not refer their patients to radiologists for medical imaging use imaging more frequently than do physicians who refer their patients to radiologists (4–6). Those studies, based on episode-of-care analyses of health insurance claims data from the 1980s, were published prior to the enactment of legislation aimed at preventing self referral in some settings. Studies documenting the increased performance of imaging by nonradiologists (1,2) did not use an episode-of-care analytic approach; thus, their findings may represent, at least in part, a change in the relative proportion of imaging procedures performed by radiologists and by nonradiologists rather than an increase in utilization on the part of self-referring or same-specialty–referring physicians per se. The purpose of our study, therefore, was to retrospectively compare the frequency with which patients underwent diagnostic medical imaging procedures during episodes of outpatient medical care according to whether their physicians referred patients for imaging to themselves and/or physicians in their same specialty or to radiologists.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Data Acquisition and Analysis
For our Health Insurance Portability and Accountability Act–compliant study, we obtained access to the claims for a large national employer-based health plan (our Data Use Agreement with the health plan precludes its specific identification). The approximately 4 million enrollees include employees, retirees, and their dependents. They are distributed across the United States and are sociodemographically mixed. A deidentified (both patients and physicians) data extract for the years 1999 through 2003 provided more than 526 000 000 claims. Because of the deidentified nature of the health plan claims database, our study did not require institutional review board approval or informed consent. The health plan is able to make its deidentified claims data available to researchers who sign a Data Use Agreement. Separate files provided information regarding each member and provider and details of each claim for professional and other services, inpatient stays, and pharmacy use. These data were merged into a single database.

The data were processed (H.S.R., A.C.T.) by using episodic analysis software (ETG Grouper; Ingenix/Symmetry Products, Phoenix, Ariz), resulting in the identification of "episodes" of care. Each episode consisted of one or more records for a member, comprising an illness. The software assigns each episode to an underlying Episode Treatment Group. Episodes relating to each of six conditions (cardiopulmonary disease, coronary and/or cardiac disease, extremity fracture, knee pain, intraabdominal malignancy, stroke) were identified by means of these Episode Treatment Groups.

All inpatient care claims were then eliminated. For each episode, a "referring physician" was defined as the physician who billed for an office visit. Episodes with more than one such referring physician were eliminated. One-physician episodes comprised approximately 76% of all valid episodes in the study data set.

Imaging procedures of interest were identified (G.S.G.) for each condition (Table 1). For stroke and knee pain, we separately evaluated CT and MR imaging.


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  		Table 1. Conditions and Imaging Procedures Evaluated

 
For each imaging claim, the provider of professional services was identified. That provider's specialty (as indicated in the claims database) was contrasted with the specialty of the referring physician. Each imaging claim was then categorized as being by a radiologist (RAD), a provider with the same specialty as the referring physician (SAME), a provider with some other known specialty (OTHER), or none of the above (MISSING). All episodes with imaging for each referring physician were evaluated. Each referring physician was then assigned to one of six categories on the basis of that physician's pattern of referral for imaging procedures: all imaging by radiologists (ALL RAD), all imaging by same-specialty providers (ALL SAME), most (80%–99%) imaging by radiologists (MOST RAD), most imaging by same-specialty providers (MOST SAME), not predominantly (21%–79%) either (MIXED), and INDETERMINATE. The INDETERMINATE group consisted of physicians whose referring behavior could not be determined from the available data. These physicians either never referred patients for imaging (for the condition of concern) or all of their imaging referrals were categorized as OTHER or MISSING. For most conditions, such physicians accounted for less than 4% of all referring physicians, except in the case of evaluation of knee pain with radiography (20.7%) and evaluation of extremity fracture with radiography (48.8%).

Analyses were performed to compare ALL RAD with ALL SAME referring physicians and also to compare 80% or more RAD (MOST RAD and ALL RAD) with 80% or more SAME (MOST SAME and ALL SAME). For brevity, we present only results of those analyses contrasting ALL RAD with ALL SAME.

Statistical Analysis
For each combination of condition, imaging procedure, and referring physician type, the number of referring physicians, the total number of episodes, the total number of episodes with imaging, the percentage of episodes with imaging, and the total number of episodes with imaging on the same date as the office visit were calculated. To assess the comparability of patients seen by ALL RAD and ALL SAME referring physicians, patient age and a comorbidity score (the number of distinct diagnoses in all of the claims for the episode [one, two, three, four, or five or more] [7,8]) were also calculated for each combination of condition, imaging procedure, and referring provider type. These measures were then compared by using t tests and continuity-adjusted {chi}2 tests for contingency tables, as appropriate. Logistic regression was then used to determine whether there was a difference between ALL RAD and ALL SAME referring physicians in the likelihood that imaging would be performed (for each condition–imaging procedure combination) after controlling for patient age and comorbidity (ie, age and comorbidity were included as covariates). P values of .008 or less were considered to indicate statistically significant differences (to adjust for the multiple comparisons in our study of six conditions).

To investigate the variability among referring physicians of each type regarding the likelihood that an episode would have imaging, the fraction of episodes with imaging was calculated for each referring physician. The standard deviation was then calculated for all physicians of each type with at least six episodes in the condition of concern. (The fraction of episodes with imaging among referring physicians who were classifiable [ie, not INDETERMINATE] was biased, because all physicians must have had at least one episode with imaging. Referring physicians with five or fewer episodes were excluded to reduce this bias). All analyses were performed (A.C.T., E.F.H.) by using statistical software (SAS, version 9.1; SAS Institute, Cary, NC).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
A total of 18 123 121 episodes of care associated with 882 687 referring physicians were analyzed. The study population was 45% male and 55% female; 1% of the population was 0–34 years old, 6% were 35–54 years old, and 93% were 55 or older. Table 2 summarizes the raw numbers and percentages of referring physicians, episodes, episodes with imaging (as a percentage of all episodes), episodes with imaging on the same day as the office visit (as a percentage of episodes with imaging), and the standard deviation across referring physicians within each type (ALL SAME, ALL RAD) for the percentage of episodes with imaging (for referring physicians with six or more episodes).


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  		Table 2. Numbers of Physicians and Episodes, Frequencies of Imaging and Same-Day Imaging, and Variation in Imaging Utilization

 
Within the condition–imaging procedure combinations evaluated, physicians who referred their patients to themselves or to other physicians in the same specialty for diagnostic imaging used imaging between 1.12 and 2.29 times as often, per episode of care, as did physicians who referred their patients to radiologists. The variation in imaging utilization among physicians with at least six episodes within a given condition–imaging procedure combination was substantially larger among same-specialty–referring physicians than among radiologist-referring physicians. In seven of the eight condition–imaging procedure combinations, patients seen by same-specialty–referring physicians were more likely to undergo imaging on the same day as an office visit (range, 0.93–2.5 times as often).

Table 3 summarizes the age and comorbidity score (number of distinct diagnoses) for each combination of condition, imaging procedure, and referring provider type. Mean patient age was greater among patients seen by same-specialty–referring physicians in six of eight condition–imaging procedure combinations, while the comorbidity score was greater for patients seen by radiologist-referring providers in all eight combinations.


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  		Table 3. Age of and Number of Diagnoses for Patients Seen by SAME versus RAD

 
Table 4 contains the results of the logistic regression analysis of the chance that an episode would include imaging. The odds ratio is for ALL SAME versus ALL RAD, controlling for patient age and number of diagnoses. P values are imprecise, because no adjustment was made for clustering of episodes for the same patient or same referring physician. However, given the strength of the P values and the related narrowness of the confidence intervals, we can be confident that these effects would remain significant even if there were much greater intercorrelation of clustered data than is likely.


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  		Table 4. Results of Logistic Regression Analysis of Likelihood of Imaging

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
For the conditions and imaging procedures evaluated, physicians who referred their patients for diagnostic imaging to themselves or to other physicians in the same specialty used imaging 1.12–2.29 times more frequently than did physicians who referred their patients to radiologists. The variation in imaging utilization among same-specialty–referring physicians was also significantly greater than among radiologist-referring physicians. These differences cannot be attributed to differences in case mix, because analyses were performed within specific Episode Treatment Groups. Similarly, the logistic regression analysis with patient age and comorbidity as covariates showed that the differences could not be attributed to differences in age or comorbidity. After controlling for patient age and comorbidity, the likelihood of undergoing an imaging procedure was 1.196–3.228 times greater for patients cared for by same-specialty–referring physicians than for patients cared for by radiologist-referring physicians. In seven of eight comparisons, the odds ratios favoring increased imaging by same-specialty–referring physicians were greater than the unadjusted ratios.

The results of previous studies that used a similar episodic analytic approach have generally been similar (4–6), although the magnitude of the increased utilization was less in the current study than in those of Hillman (4) and Hillman et al (5). Differences may be due, at least in part, to the enactment of legislation aimed at limiting self-referral in some settings. Compared with previous studies, our study used a larger claims data set, evaluated the effects of same-specialty referral rather than strictly self-referral, assigned referring physicians to referral categories by using a more restrictive definition, and, through logistic regression, attempted to control for differences in patient age and comorbidity. Our study population, derived from a large national employer-based health plan, includes employees, retirees, and their dependents. It is geographically and sociodemographically diverse and may be more representative of the U.S. population than the data sets used by Hillman (4) and Hillman et al (5).

We chose to look at same-specialty referral instead of just self-referral because "self-referral" may represent referral to one's partners or colleagues. This broader definition may have resulted in the inclusion of some physicians with no financial or other relationship with the referring physician and may thus have reduced the magnitude of the observed increase in utilization (ie, if same-specialty–referring physicians without financial relationships did not demonstrate increased utilization of diagnostic imaging, their inclusion would have diluted the effect). Compared with Hillman (4) and Hillman et al (5), who defined self-referring physicians as individuals who charged at least once for an imaging procedure, we categorized referring physicians on the basis of their entire referral history for the condition of concern. Same-specialty referrers must have always referred patients to themselves or to others in the same specialty. Finally, our logistic regression analysis, which controlled for patient age and comorbidity, may provide a more accurate estimate of the effect of same-specialty referral on the utilization of diagnostic imaging procedures.

We based our methods on those of prior studies and attempted to improve on those methods where possible. Nevertheless, our study had several potential limitations. First, categorization of referring physician behavior was not possible in some instances, where either physicians only referred patients to an imaging provider with some other known specialty or the specialty of the imaging provider could not be identified. These physicians accounted for a small percentage of all referring physicians. Our results are based on those referring physicians whose referral behavior could be accurately categorized. Second, because we categorized referral behavior on the basis of the specialty associated with the professional (rather than technical) component of the imaging claim, we may have missed cases of same-specialty referral where the professional component (ie, interpretation only) was subcontracted out to a radiologist. Finally, we did not look at imaging facility ownership because this information was not available in the claims data set.

Our findings should be of interest to regulatory and reimbursement agencies and other groups that are trying to manage trends in imaging utilization. It is not possible to determine from our results if the increased utilization of same-specialty–referring physicians represents better care or results in better patient outcomes. It is also not possible to determine the extent to which financial incentives may explain the greater utilization. However, the magnitude of our findings and their consistency with those of other studies suggest that financial incentives may play a role. It may also be that patients are more likely to adhere to recommendations to undergo imaging procedures if the procedures can be performed on the same day as office visits, and our study results did demonstrate that patients seen by same-specialty–referring physicians more often underwent imaging on the same day as an office visit. Finally, there may be some selection bias involved if physicians who for some reason are more likely to order imaging procedures tend to acquire imaging equipment themselves or to affiliate with others in the same specialty who do so.

In conclusion, our results demonstrate that same-specialty–referring physicians tend to utilize imaging more frequently than physicians who refer their patients to radiologists. These findings were consistent across the eight combinations of conditions and imaging procedures evaluated and cannot be explained by differences in case mix, patient age, or comorbidity.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 


   IMPLICATION FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
References
 


   FOOTNOTES
 
Author contributions:Guarantor of integrity of entire study, G.S.G.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, G.S.G., H.S.R., A.C.T.; statistical analysis, all authors; and manuscript editing, all authors

Authors stated no financial relationship to disclose.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 

  1. Maitino AJ, Levin DC, Parker L, Rao VM, Sunshine JH. Practice patterns of radiologists and nonradiologists in utilization of noninvasive diagnostic imaging among the Medicare population 1993–1999. Radiology 2003;228:795–801. [Abstract/Free Full Text]
  2. Maitino AJ, Levin DC, Parker L, Rao VM, Sunshine JH. Nationwide trends in rates of utilization of noninvasive diagnostic imaging among the Medicare population between 1993 and 1999. Radiology 2003;227:113–117. [Abstract/Free Full Text]
  3. Thompson DF. Understanding conflicts of interest. N Engl J Med 1993;329:573–576. [Free Full Text]
  4. Hillman BJ. Frequency and costs of diagnostic imaging in office practice: a comparison of self-referring and radiologist-referring physicians. N Engl J Med 1990;323:1604–1608. [Abstract]
  5. Hillman BJ, Olson GT, Griffith PE, et al. Physicians' utilization and charges for outpatient diagnostic imaging in a Medicare population. JAMA 1992;268(15):2050–5054.
  6. Referrals to physician-owned imaging facilities warrant HCFFA's scrutiny: report to the chairman. Subcommittee on Health. Committee on Ways and Means. House of Representatives. Washington, DC: U.S. General Accounting Office, 1994; 1–61.
  7. Melfi C, Holleman E, Arthur D, Katz B. Selecting a patient characteristics index for the prediction of medical outcomes using administrative claims data. J Clin Epidemiol 1995;48:917–926. [CrossRef][Medline]
  8. Rochon PA, Katz JN, Morrow LA, et al. Comorbid illness is associated with survival and length of hospital stay in patients with chronic disability: a prospective comparison of three comorbidity indices. Med Care 1996;34(11):1093–1101.



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