Special Article
Frequency and Costs of Diagnostic Imaging in Office Practice — A Comparison of Self-Referring and Radiologist-Referring Physicians
N Engl J Med 1990; 323:1604-1608December 6, 1990
- Abstract
- Abstract
Background.
To assess possible differences in physicians' practices with respect to diagnostic imaging, we compared the frequency and costs of imaging examinations as performed by primary physicians who used imaging equipment in their offices (self-referring) and as ordered by physicians who always referred patients to radiologists (radiologist-referring).
Methods.
Using a large, private insurance-claims data base, we analyzed 65,517 episodes of outpatient care by 6419 physicians for acute upper respiratory symptoms, pregnancy, low back pain, or (in men) difficulty urinating. The respective imaging procedures studied were chest radiography, obstetrical ultrasonography, radiography of the lumbar spine, and excretory urography, cystography, or ultrasonography.
Results.
For all four clinical presentations, the self-referring physicians obtained imaging examinations 4.0 to 4.5 times more often than the radiologist-referring physicians (P<0.0001 for all four). For chest radiography, obstetrical ultrasonography, and lumbar spine radiography, the self-referring physicians charged significantly more than the radiologists for imaging examinations of similar complexity (P<0.0001 for all three). The combination of more frequent imaging and higher charges resulted in mean imaging charges per episode of care that were 4.4 to 7.5 times higher for the self-referring physicians (P<0.0001). These results were confirmed in a separate analysis that controlled for the specialty of the physician.
Conclusions.
Physicians who do not refer their patients to radiologists for medical imaging use imaging examinations more frequently than do physicians who refer their patients to radiologists, and the charges are usually higher when the imaging is done by the self-referring physician. From our results it is not possible to determine which group of physicians uses imaging more appropriately. (N Engl J Med 1990; 323:1604–8.)
Media in This Article
Table 1
Categories of Physicians and Episodes, Frequencies of Imaging, and Imaging Costs in One-Physician Episodes.*Table 2
Frequency of Imaging and Costs per Episode in One-Physician Episodes, According to the Specialty of the Physician.*Article Activity
- Article
THE potential for conflicts of interest and higher costs for health care arising from the ownership by physicians of the diagnostic facilities to which they refer patients has attracted considerable attention recently in the medical literature1 2 3 4 5 and lay press6 , 7 and has been the subject of government study and legislation.8 9 10 The ownership of imaging centers by physicians has received much of the media attention. However, most self-referral for medical imaging — in which physicians perform and interpret diagnostic imaging examinations of their own patients rather than refer them to imaging specialists — takes place in the physician's office.
The few previous studies investigating the effect of self-referral on the use and costs of imaging have been limited by methodologic flaws, small study populations, and lack of controls. To overcome these limitations, we analyzed a large data base of private insurance claims and evaluated the imaging done in physicians' offices during episodes of outpatient medical care. After controlling for differences in patients' clinical presentations and physicians' specialties, we compared the frequencies with which the patients underwent imaging examinations during episodes of medical care for acute conditions, according to whether their physicians could perform those imaging examinations themselves. We also compared the resultant charges for the imaging examinations.
Methods
Selection of Data Base and Clinical Presentations
We purchased access to a data base (Medstat Systems, Ann Arbor, Mich.) comprising all the health insurance claims of 403,458 employees and dependents of several large American corporations. The insurance programs provided comprehensive coverage, including outpatient imaging services, with no copayments required. The data base was selected for its uniformity and completeness. Seventy-nine percent of the study population lived in the north central United States, 6 percent in the Northeast, 11 percent in the South, and 4 percent in the West. Fifty-one percent were female, and 49 percent male. Fifty-five percent were 0 to 34 years old, 33 percent were 35 to 54 years old, and 12 percent were 55 or older. Ninety-three percent of the physicians making claims for care provided to these patients practiced in metropolitan areas.
Using this data base, we compared the frequency of imaging and the charges for imaging among self-referring physicians and among physicians who instead referred patients to radiologists (radiologist-referring physicians) for four clinical presentations, selected for their variety and the volume of associated imaging procedures. The presentations, with the associated diagnostic inquiry, were as follows: acute upper respiratory symptoms (Was chest radiography performed?), pregnancy (Was obstetrical ultrasonography performed to assess fetal size and gestational age?), low back pain (Was radiography of the lumbar spine performed?), and (in men) difficulty urinating (Was excretory urography, cystography, or ultrasonography performed?).
Definition and Initiation of Episodes
We surveyed the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM),11 selecting all codes that might reasonably represent diagnoses that would be entered by physicians whose patients presented with symptoms related to any of the four clinical presentations. A detailed tabulation of the codes is available elsewhere.*
We developed and applied to the claims data base a computer algorithm, modeled on previous methods, for defining episodes of outpatient medical care occurring in physicians' offices.12 The date of a claim for an index ICD-9-CM code in an office setting was used to define the starting date of an episode. Episodes were considered to have ended after specified periods — four weeks for upper respiratory infection, nine months for pregnancy, six weeks for low back pain, and six weeks for difficulty urinating. Claims made between the initiation and termination dates of an episode were eligible for inclusion in that episode. Depending on the clinical presentation, a lag period of two to eight weeks followed the termination of each episode, so that follow-up visits for the original episode would not be counted as new episodes of care. The length of the episodes and lag periods was initially proposed on the basis of medical experience. We ensured that these durations were appropriate by evaluating the completeness of 600 randomly selected episodes and determining that the use of alternate durations for the episodes of up to two-thirds longer affected the number of episodes by only 1 to 6 percent in the case of the clinical presentations studied.
To be included in the study, episodes of care had to begin after January 1, 1986, and end before June 1, 1988. Episodes were excluded if the only physician involved in the episode was a radiologist or if the specialty of any physician involved was unknown. Within valid episodes, we deleted any claims for which no charge or payment was made, any claims for supplemental payments, and any claims for which the age or sex of the patient or the physician's identification number was unknown. We also excluded claims that were unrelated in terms of ICD-9-CM coding to the clinical presentations under investigation and claims made by physicians whose specialty codes indicated practices unrelated to the clinical presentations under study. A list of the specialties of the physicians included in the analysis is available elsewhere.*
Categorization of Physicians and Classification of Episodes
The physicians who filed the claims included in the episodes studied were distinguished by their physician identification numbers; these numbers were coded to protect confidentiality. With regard to each clinical presentation, the physicians were grouped, according to their involvement in episodes for which they were the only nonradiologist physician to file a claim (one-physician episodes), into the following categories: self-referring physicians, who charged at least once for an index imaging examination; radiologist-referring physicians, who never charged for an index imaging examination and who were involved in at least one one-physician episode in which a radiologist performed such an examination; and physicians whose patients had no imaging in any one-physician episodes. One-physician episodes comprised 92 percent of all valid episodes.
We considered the possibility that some physicians categorized as radiologist-referring might actually be self-referring physicians who happened not to have performed any imaging in the episodes in our sample. We performed a correction to account for this possibility (details available elsewhere*). Since this correction did not alter the results, we report only our unadjusted data here.
The categorization of the physicians who participated in the one-physician episodes was used to develop six categories of similar and dissimilar pairs of physicians for the 7 percent of valid episodes in which two different physicians, neither a radiologist, cared for the patient (two-physician episodes). The 471 valid episodes (0.7 percent) in which more than two nonradiologist physicians were involved were not included in the analysis. We performed separate classifications of the one-physician and two-physician episodes on the basis of the categorization of the physicians and whether a claim for a related imaging examination was filed during the episode, as evidenced by the encountering of an appropriate diagnostic-imaging-procedure code (CPT-4 code; the table of index codes is available elsewhere*).
*See NAPS document no. 04816 for 16 pages of supplementary material. Order from NAPS c/o Microfiche Publications, P.O. Box 3513, Grand Central Station, New York, NY 10163–3513. Remit in advance (in U.S. funds only) $7.75 for photocopies or $4 for microfiche. Outside the U.S. and Canada add postage of $4.50 ($1.50 for microfiche postage).
Estimation of the Frequency of Imaging
For the one-physician episodes, our estimates of the frequency of imaging by the self-referring physicians and the radiologist-referring physicians were based on the observed frequencies for these two categories of physicians. Applying maximum-likelihood methods to the information we derived from our data about the imaging practices of self-referring and radiologist-referring physicians, we adjusted these observed frequencies to account for the episodes attributable to the physicians who had performed no imaging. This adjustment was based on the assumption that the imaging practices of the physicians within each category were homogeneous. However, this was almost certainly not the case. As a result, the correct adjustment of the observed frequencies is uncertain. For this reason, we report here the most likely estimates of the imaging frequencies for the self-referring and the radiologist-referring physicians. In addition, to account for heterogeneity in the physicians' imaging practices, we developed estimates biased upward and downward that show that our results are not affected qualitatively by the choice of the adjustment for the episodes involving the physicians who performed no imaging over the entire range of possible adjustments. The methods we employed, the initial categorization of the physicians and classification of episodes, and the upward- and downward-biased estimations of imaging frequencies are available elsewhere.*
Statistical Analysis
For the analyses of both the one-physician and the two-physician episodes, we assessed the differences between self-referring and radiologist-referring physicians in terms of the proportion of episodes that involved imaging, the charges for imaging performed, and the average imaging charges per episode. To calculate the results for the group, we weighted the results for individual physicians according to the number of episodes in which they were involved. The significance of the differences between self-referring and radiologist-referring physicians was determined by the usual t-statistic for the difference in means between the two groups. We conducted a similar analysis based on the specialties of the physicians involved in the episodes, to compare differences within specialties. The null hypothesis of no difference was rejected at a P level of <0.05.
Complexity of Imaging Procedures
For each clinical presentation, we compared the complexity of the imaging examinations performed by the self-referring physicians with that of the examinations performed by the radiologists by calculating the mean (±SD) relative values of their procedures (i.e., a measure of the complexity of the procedure).13
Results
One-Physician Episodes
The data base generated 62,880 one-physician episodes for the four study groups. After exclusions (see Methods), there were 60,829 valid episodes involving 6419 physicians. One-physician episodes represented 92 percent of all valid episodes. These were distributed as follows: upper respiratory symptoms, 47,794 episodes involving 3452 physicians; normal pregnancy, 1377 episodes involving 468 physicians; back pain, 9634 episodes involving 2001 physicians; men with difficulty urinating, 2024 episodes involving 498 physicians.
Table 1Table 1
Categories of Physicians and Episodes, Frequencies of Imaging, and Imaging Costs in One-Physician Episodes.* shows the frequencies with which imaging was used during the episodes, the charges for imaging, and the charges for imaging per episode for self-referring and radiologist-referring physicians. The mean imaging charges of the self-referring physicians were significantly higher (P for all comparisons, <0.0001) than those of the radiologists for all clinical presentations except difficulty urinating. Depending on the clinical presentation, the episodes involving self-referring physicians resulted in imaging 4.0 to 4.5 times as frequently, with average imaging charges per episode 4.4 to 7.5 times higher than those for the episodes involving radiologist-referring physicians (P<0.0001 for each clinical presentation, for both frequency of imaging and average imaging charges per episode).Two-Physician Episodes
There were 4688 valid two-physician episodes, or 7 percent of all episodes. The results for these episodes support the findings in the one-physician episodes. Depending on the clinical presentation, the episodes involving two self-referring physicians were 1.7 to 3.7 times as likely to result in imaging as episodes involving two radiologist-referring physicians (P<0.01 for each presentation). Complete results for all six categories of physician pairs are available elsewhere.*
Differences among Specialties
For each specialty and each clinical presentation, the self-referring physicians performed imaging 2.4 to 11.1 times as often as the radiologist-referring physicians, and at a cost per episode for imaging that was 3.0 to 17.1 times higher, depending on the specialty and clinical presentation (Table 2Table 2
Frequency of Imaging and Costs per Episode in One-Physician Episodes, According to the Specialty of the Physician.*) (P<0.01 for each specialty studied with regard to each clinical presentation).Complexity of Imaging Examinations
The mean (±SD) complexity score for chest films was 3.02±0.14 for self-referring physicians, and 3.00±0.20 for radiologist-referring physicians. For obstetrical ultrasonography, the comparison was 11.24±1.14 versus 11.35±0.96; for lumbar spine films, 3.98±0.63 versus 4.14±0.52; and for the combination of urography, cystography, and ultrasonography, 8.46±0.70 versus 8.35±0.43. Thus, the differences in complexity ranged from 1 to 4 percent and do not account for the differences identified in the charges for imaging.
Discussion
For the clinical presentations we studied, patients with similar sets of symptoms were at least four times as likely to have diagnostic imaging performed as part of their evaluation if they sought care from a physician who performed imaging examinations in the office rather than from one who referred patients to a radiologist. Because self-referring physicians performed imaging studies more frequently and generally charged more than radiologists for similar imaging procedures, patients seeking care from self-referring physicians incurred considerably higher charges for diagnostic imaging than patients whose physicians referred them to radiologists. These effects cannot be attributed to differences in the mix of patients, the specialties of the physicians, or the complexity of the imaging examinations performed.
Previously, Childs and Hunter14 found that physicians other than radiologists who provided imaging services used imaging more frequently than their peers in caring for elderly patients in Northern California. In a 1978 survey of 5447 physicians, Radecki and Steele15 determined that nonradiologist physicians with imaging facilities either in their offices or at the same site have higher rates of use than physicians without such facilities. A similar study of the effect ofthe site of imaging facilities used by family practitioners produced a similar result.16
The differences between our study and those performed previously include the relatively large number of patients and physicians we studied and the emphasis on specific clinical situations and episodes of medical care. Analyzing episodes of care permitted us to focus directly on the issue that seemed most pertinent — whether individual patients with specific symptoms were more likely to receive imaging examinations when their physicians operated imaging equipment. As compared with the global measures used in previous studies, this method controls better for other variables — physicians' specialization, the complexity of examinations, differences in the types of patients seen by physicians, and the number of patient—physician encounters that might occur during the course of a patient's medical care. Finally, the focus on episodes as the unit of analysis allows a more accurate assessment of the activities and costs of medical care, the chief focus of our study.12
We have attempted to account for what we perceive to be the major possible biases of our study. After assessing the effect of correcting our results to account for the small percentage of physicians who had probably been miscategorized, and evaluating alternative probabilistic models for assigning the episodes involving physicians whom we could not categorize definitively, we found that these considerations did not affect the results qualitatively (details of these assessments and the adjusted results are available elsewhere*). Our population of patients did not represent the American population, geographically or according to age. However, the geographic concentration tended to lessen the effects of regional differences in practice patterns, and it seems implausible that the large differences we identified in the use of imaging would be related to age. Although there is no assurance that the clinical presentations we studied represent the imaging practices of physicians in other clinical settings, the dimensions and consistency of our findings with regard to four very different clinical presentations and types of imaging examinations suggest that this practice pattern may be widespread.
We based our methods on those used by previous investigators,12 , 17 , 18 but with adaptations to account for the large number of physicians and patients in our data base. Doubtless, the initial visits to physicians that triggered episodes of outpatient care occurred in an undefined context of patients' seeing their personal physicians, being referred by one physician to another, and seeking the specialist they believed to be appropriate. Although the manner in which the patients ended up seeing the physicians they did might potentially have affected the results, it is important to note that the results were uniformly sustained in our analysis of individual specialties. Also, with regard to our means of defining the index symptoms, determining the start of episodes, and including claims in episodes, there is nothing to suggest that our choices unequally biased the probability of imaging or the imaging charges in favor of either self-referring or radiologist-referring physicians. We believe that the differences between these two groups of physicians are so considerable that such issues have little relevance to the results.
Our findings of increased use of imaging and increased costs attributable to nonradiologist physicians who operate their own imaging equipment should be of interest to regulatory and reimbursement agencies. It is impossible to determine from our results whether the imaging practices of the self-referring physicians or those of the radiologist-referring physicians represent the more appropriate care. Nor is it possible to determine the extent to which financial incentives are responsible for the higher levels of use and charges among the self-referring physicians. These physicians may perform imaging more frequently because they have financial incentives to do so, because imaging is more convenient when performed in a physician's office, or because physicians who perform imaging more often are more likely to acquire imaging equipment. Nonetheless, the differences between the self-referring and radiologist-referring physicians in the use of imaging are so large that some concern over the role of financial incentives must be invoked. Schroeder and Showstack19 have detailed the potent financial incentives for a physician to incorporate imaging into an office practice. More recently, Hemenway et al.20 validated this concern by showing an increase in the use of imaging when a group of ambulatory clinics changed to a method of compensation that used the frequency with which physicians ordered imaging examinations as the basis for paying them.
The American Medical Association has stated that the referral of patients to facilities in which physicians have an ownership interest is permissible, provided that patients are apprised of this relation and have other choices, and provided that physicians always act in their patients' best interests.21 With respect to diagnostic imaging, however, it is unlikely that patients, even if so apprised, will be able to assess the appropriateness of such referrals accurately or seek imaging elsewhere. Particularly in the office setting, patients cannot be said to have a meaningful choice when their physicians advise them to undergo imaging. The potential to self-refer patients for imaging must surely complicate physicians' decisions and perhaps jeopardize their obligation to place their patients' interests above their own.
*See NAPS document no. 04816 for 16 pages of supplementary material. Order from NAPS c/o Microfiche Publications, P.O. Box 3513, Grand Central Station, New York, NY 10163–3513. Remit in advance (in U.S. funds only) $7.75 for photocopies or $4 for microfiche. Outside the U.S. and Canada add postage of $4.50 ($1.50 for microfiche postage).
Supported by the American College of Radiology.
We are indebted to Medstat Systems, Inc., for assistance in providing access to the insurance-claims data base and help in developing the algorithm used to identify episodes of outpatient care; to Dr. Barbara J. McNeil for reviewing the penultimate version of the manuscript and making suggestions for its improvement; and to Ms. Janet Wallace for her help and patience during numerous revisions of the manuscript.
Source Information
From the Department of Radiology, the University of Arizona College of Medicine, Tucson (B.J.H.); the Health Research Area, Abt Associates, Cambridge, Mass. (C.A.J., S.D.K., M.N.); and the Research Division, the American College of Radiology, Reston, Va. (M.R.M., J.H.S.). Address reprint requests to Dr. Hillman at the Department of Radiology, University Medical Center, Tucson, AZ 85724.
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