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Nationwide Trends in Rates of Utilization of Noninvasive Diagnostic Imaging among the Medicare Population between 1993 and 1999¹

¹ From the Department of Radiology, Thomas Jefferson University Hospital, Suite 3390, Gibbon Bldg, 111 S 11th St, Philadelphia, PA 19107 (A.J.M., D.C.L., L.P., V.M.R.); and American College of Radiology, Reston, Va (J.H.S.). From the 2001 RSNA scientific assembly. Received May 24, 2002; revision requested July 16; revision received August 1; accepted September 24. Address correspondence to A.J.M. (e-mail: andrea.maitino@mail.tju.edu).

	ABSTRACT

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PURPOSE: To determine current utilization rates and recent nationwide trends for noninvasive diagnostic imaging (NDI) among the Medicare population.

MATERIALS AND METHODS: Medicare Part B claims data files from 1993, 1996, and 1999 were analyzed for all procedure codes related to NDI. NDI codes were grouped into 22 imaging categories, as well as seven imaging modality groups. The data were analyzed to determine the overall nationwide utilization and relative value unit (RVU) volume and rates and changes in utilization rates and RVU rates between 1993 and 1999 for the Medicare fee-for-service population, which included approximately 33 million enrollees per year.

RESULTS: The overall utilization rate for all NDI in 1999 was 324,974 examinations per 100,000 enrollees. Conventional radiography was the most utilized imaging technology (55.5%), followed by ultrasonography (US) (20.5%), computed tomography (CT) (8.8%), mammography (6.0%), nuclear imaging (5.2%), magnetic resonance (MR) imaging (2.6%), and bone densitometry (1.5%) (percentages do not add up to 100% due to rounding). In the 6-year interval from 1993 to 1999, the rate of NDI utilization increased 3.8%. The utilization rate for conventional radiography decreased 13.7%, while that of all other modalities increased a combined total of 39.1%. During this 6-year period, RVU rates per 100,000 increased 14.6%, with RVUs for MR imaging increasing 76.6%; those for nuclear imaging, 38.7%; those for CT, 28.3%; and those for US, 24.2%.

CONCLUSION: A 3.8% increase in the rate of NDI utilization occurred during the 6-year period between 1993 and 1999. A considerably larger increase in RVU rates (14.6%) occurred during the same time period.

© RSNA, 2003

Index terms: Diagnostic radiology • Economics, medical • Radiology and radiologists, socioeconomic issues

	INTRODUCTION

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There is increasing concern among health policy planners that the growth in utilization of high-technology procedures, including noninvasive diagnostic imaging (NDI) procedures, is a major factor in the rapid growth in health care costs. It has been reported that the utilization of NDI in populations of commercially insured patients younger than 65 years is 758 studies per 1,000 subscribers per year (1). In populations of patients younger than 65 years enrolled in health maintenance organizations, mean utilization is 666 studies per 1,000 (1). There are few published data available, however, on the utilization of NDI among the Medicare population.

Researchers at the Centers for Medicare and Medicaid Services (CMS) have estimated that there will be 60.6 million individuals over the age of 65 years by the year 2025, a 74% increase from 1998 (2). With Medicare reimbursing approximately one-third of all medical services in the United States (1), utilization of health care services among the Medicare population is of great importance in predicting the future health care resources needed in the United States. Thus, the purpose of this study was to determine the current utilization rates and recent nationwide trends for NDI among the Medicare population.

	MATERIALS AND METHODS

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The nationwide CMS Part B Physician/Supplier Procedure Summary Master Files (the Medicare Part B databases) for 1993, 1996, and 1999 were examined. These files include all Medicare fee-for-service enrollees but do not include those in health maintenance organizations. The Medicare Part B databases are public files and are therefore exempt from institutional review board and informed consent regulations. We evaluated all current procedural terminology codes (ie, CPT-4 codes) related to NDI as performed by both radiologists and nonradiologists; the codes were selected from the fourth edition of Physician’s Current Procedural Terminology for 1993 (3), 1996 (4), and 1999 (5).

These codes are designated by the American Medical Association and are referred to by CMS as Level I Healthcare Common Procedure Coding System (HCPCS) codes. For each code, the Medicare Part B files provide health care utilization data on claims, procedure volumes, charges, reimbursements, specialty of the physician provider, and other factors. NDI codes used for this evaluation included most codes in the 70,000 series (which are generally thought of as those applicable to radiologic procedures) and codes for cardiac and vascular ultrasonographic (US) procedures, which are listed in the 90,000 series. This analysis excluded surgical codes, the radiologic supervision and interpretation codes that accompany surgical codes, and codes for radiation oncology procedures, ophthalmic US, three-dimensional reconstruction of computed tomographic (CT) and magnetic resonance (MR) images, and radioimmunoassays. Obstetric US was included in this analysis, although this examination is not often performed in the Medicare population (in all likelihood, obstetric US examinations were performed only in patients with chronic renal failure, who are covered by Medicare, and in disabled beneficiaries of Medicare).

We also included the imaging-related Level II HCPCS codes, which are five-position alphanumeric codes that are approved and updated jointly by the Alpha-Numeric Editorial Panel (consisting of members of CMS, the Health Insurance Association of America, and the Blue Cross and Blue Shield Association). These alphanumeric codes are sometimes used in obtaining reimbursement for procedures before a CPT-4 code has been established by the American Medical Association. The alphanumeric Level II HCPCS codes related to NDI were selected from the HCPCS files (6) and comprised less than 1% of all the codes for the NDI examinations in this analysis.

The total number of codes studied in each of the 3 years varied owing to the formation of new codes and the discontinuation of outdated codes, thereby resulting in an analysis that included 364 codes in 1993, 385 in 1996, and 428 in 1999. The utilization rates and relative value unit (RVU) rates per 100,000 Medicare fee-for-service enrollees were calculated for 1993, 1996, and 1999 on the basis of data in the Medicare county data files (7), which indicated that there were 33,299,906 such enrollees in 1993, 32,396,579 in 1996, and 33,550,219 in 1999.

We chose to consider NDI as encompassing seven modalities (radiography, mammography, US, CT, MR imaging, nuclear imaging, and bone densitometry); these seven modalities were further classified into a total of 22 diagnostic categories. The total procedure volume and Medicare Part B professional component RVUs were determined for each corresponding NDI code in 1999. The nationwide number of RVUs for each code were calculated by multiplying the 1999 Medicare professional component RVUs assigned to that code by the number of examinations performed. The results represent a proxy for the relative amount of work for each procedure. Because no RVUs are assigned to screening mammography in the Medicare Resource Based Relative Value Scale (8), we made the assumption that a screening mammogram should carry 80% of the professional component RVUs of a diagnostic mammogram. This was based on a recommendation of the American College of Radiology (9).

The percentage change in NDI utilization rates during the 6-year period between 1993 and 1999 was calculated for the 22 categories and seven modalities by subtracting the 1993 rate from the 1999 rate and dividing the difference by the 1993 rate. Similar calculations were performed for RVU rates. The 1999 RVU scale was used to calculate the RVU rates for 1993 and 1996 rather than the RVU scale for those particular years. We used these "synthetic" RVU rates because the assigned RVUs for some codes change from year to year, and we believed it important to use a single, consistent scale for assessment of changes in the relative amount of work. Since the Medicare Part B database represents the total fee-for-service Medicare population, and these are complete population counts, no inferential statistical analysis was required, as would be the case if we had been attempting to infer population statistics from sample data.

	RESULTS

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Procedure Volume and RVUs in 1999
Table 1 shows the total examination volume and RVUs for the 22 NDI categories and seven NDI modalities in 1999. The overall procedure volume for all NDI in 1999, the most recent year for which complete data are available, was 109,029,422 examinations. The largest category was chest radiography, accounting for 28.9% of all exams, followed by skeletal radiography (20.5%), echocardiography (12.0%), mammography (6.0%), and body CT (5.2%). The remaining categories represented less than 5% of NDI each and constituted a total of 27.4% of the NDI utilization in 1999.

A discrepancy can be noted between the percentages of the professional component RVUs and examination volumes. Although conventional radiography represented 55.5% of all imaging procedures, RVUs for conventional radiography accounted for only 25.1% of all RVUs in 1999. MR imaging, on the other hand, represented 2.6% of all imaging procedures yet corresponded to 9.1% of all RVUs.

Nationwide Trends between 1993 and 1999
Table 2 shows the nationwide utilization rates for NDI in 1993, 1996, and 1999, as well as the percentage change in utilization rates between 1993 and 1999. In 1993 the overall NDI utilization rate was 313,005 examinations per 100,000 Medicare patients. In 1999 the rate was 324,974, representing a 3.8% increase over 6 years. The variations in utilization rates between 1993 and 1999 are listed by NDI category and imaging modality in Table 2. Reductions in examinations per 100,000 Medicare patients from 1993 to 1999 were noted in general nuclear imaging (a decrease of 18.4%), spinal CT (a decrease of 15.5%), obstetric US (a decrease of 15.4%), and all four conventional radiography categories (a total combined decrease of 13.7%). The declines in these categories were offset by increases in other categories.

Nationwide trends and percentage change in professional component RVU rates between 1993 and 1999 are shown in Table 3. The overall RVU rate increased from 206,443 per 100,000 Medicare patients in 1993 to 236,649 per 100,000 in 1999, representing a 14.6% increase in RVU rates over the 6-year period. Decreases in RVU rates were observed in the same categories in which there were decreases in utilization (ie, general nuclear imaging, spinal CT, obstetric US, and all categories of conventional radiography). For most other categories, changes in the RVU rates proportional to, but slightly less than, the changes in utilization rates were demonstrated.

	DISCUSSION

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One major conclusion from this study is that the overall utilization of NDI among the Medicare population is three to four times the rate among the population of individuals younger than 65 years (1). In 1999 conventional radiography remained the most commonly performed type of examination and was utilized more than all other types of examinations combined.

Comparisons of examination volume by modality type revealed that conventional radiography represented 55.5% of all NDI in 1999. US was the second most widely used modality and represented 20.5% of NDI. CT was the third most widely used modality (8.8%). However, if one excludes echocardiography (an examination rarely performed by radiologists), overall utilization rates of US and CT are comparable. Despite the proliferation of MR imaging units in recent years, CT examinations of all types were still performed over three times as often as MR imaging examinations of all types in 1999 (9,595,885 vs 2,782,410). Body CT examinations were performed over 46 times as often as body MR examinations. Cranial CT was performed almost three times as often as cranial MR imaging. On the other hand, spinal MR was performed almost three times as often as spinal CT. In musculoskeletal imaging (including radiography, CT, and MR imaging), a total of 22,845,300 examinations were performed in 1999. CT and MR imaging accounted for only 2.0% of this total.

Total RVU volume in 1999 was calculated to be 79,396,140. Although conventional radiography accounted for over half of all NDI, its RVUs represented only 25.1% of all RVUs in 1999, indicating that the majority of NDI examinations do not account for the majority of the work. MR imaging represented the most work per imaging procedure, accounting for 9.1% of RVUs but only 2.6% of overall imaging volume.

Between 1993 and 1999, the overall utilization rate of NDI increased by only 3.8%. This slow growth suggests that physicians are not increasing their utilization of imaging to a degree that would be responsible for the high health care costs that are troubling policy makers in the United States today. These findings would seem to echo those of Sunshine et al (10), who reported, more than a decade ago, that spending on high-technology radiologic procedures (CT, MR imaging, angiography and/or interventional radiology, and US) accounted for approximately 1.5% of personal health care expenditures in 1990. During the 6-year interval evaluated in the present study, there was a considerably greater increase in RVU rates (14.6%). This indicates that the procedures currently being performed are more complex, requiring more work on the part of the physician.

Some of the 6-year trends in utilization of the different modalities and categories are of interest. The overall use of conventional radiography decreased substantially (by 13.7%), while the use of other technologies increased 39.1%. Although the utilization of advanced imaging techniques increased, they are still performed considerably less often than plain radiographic studies. Substantial technologic advances were achieved in CT and MR imaging between 1993 and 1999, yet the overall utilization of CT increased only 29.9%. The utilization of MR imaging increased more sharply (73.2%), but the overall frequency of MR imaging remained quite small in 1999 (at 2.6% of all NDI).

Between 1993 and 1999, the utilization trends for all categories remained consistent—either increasing or decreasing over the entire 6-year period—with the exception of mammography. The utilization of mammography decreased 13.1% between 1993 and 1996, and increased 34.1% between 1996 and 1999. These fluctuations in the utilization of mammography contributed to variability in the overall utilization rates of NDI, resulting in a decrease of 1.4% in the first half of the 6-year period and an increase of 5.3% during the second half.

We believe that variations in mammography utilization are related to changes in Medicare reimbursement for mammograms, as well as to the increasing awareness of breast cancer screening. In 1991, Medicare began reimbursing for biennial screening mammography, which has shown rapid increases in utilization since that year. Especially rapid increases occurred in the first years following the change in reimbursement (1991–1994). After a plateau in utilization, the change from biennial to annual reimbursement of screening mammography in 1998 led to another rapid increase in utilization.

The utilization of diagnostic mammography, on the other hand, has shown steady decreases since 1991. Some of the decline is simply a recoding of this procedure to screening mammography. This would also subject the recoded procedures to biennial and later annual limits when they had previously been unlimited. The combination of these two categories, screening mammography, the use of which is increasing, and diagnostic mammography, the use of which is decreasing, led to the pattern of overall decline in mammography utilization from 1993 to 1996, followed by an overall increase in utilization from 1996 to 1999, that was observed in this study. Other public health organizations have recorded similar trends in mammography utilization during the time frame of our study (11,12).

Bone densitometry is by far the most rapidly growing imaging technique in terms of use among the Medicare population—with a utilization increase of 2,520.0% in the 6-year period between 1993 and 1999—followed by cardiovascular MR imaging (1,113.0%), breast US (144.3%), musculoskeletal MR imaging (134.0%), and cardiovascular nuclear imaging (130.3%). Although the use of these procedures is increasing the most rapidly, total utilization for the five combined represented only 5.7% of all NDI utilization in 1999.

The rapid increase in the utilization of bone densitometry is related to two factors. First, dual energy x-ray absorptiometry (the most popular technique) was a new technology for which no code even existed in 1993. Second, more attention has been focused in recent years on osteoporosis and the need for early diagnosis and treatment. The rapid increase in utilization of cardiovascular MR is also code related. In 1993 no codes existed for MR angiography. By 1996 codes were in existence, but many local Medicare Part B carriers did not recognize or reimburse for them. By 1999, recognition of and reimbursement for these codes had become much more widespread.

Some increases in NDI utilization may be a result of self-referral. In 1990 and 1992 Hillman et al (13,14) suggested that self-referral for imaging examinations resulted in more frequent utilization. Echocardiography, a procedure almost always performed by cardiologists or other internists (15,16), is by far the most commonly performed advanced imaging technique (12.0% of all NDI procedures in 1999), and its utilization is growing steadily (with an increase of 49.6% between 1993 and 1999). Cardiovascular nuclear imaging and vascular US are other examples of procedures frequently performed by nonradiologists that also showed a considerable increase in utilization.

There were limitations in this study. This was a secondary analysis of an administrative Medicare data set. The data set provides only pure utilization information that applies to a restricted set of procedures among the fee-for-service Medicare population. The conclusions based on these data may not represent conclusions about the utilization of NDI among other insured populations.

In conclusion, NDI utilization among the Medicare population is more than four times higher than it is among those younger than 65 years. Aging of the population in future decades will have a substantial effect on the demand for NDI and radiologic resources. The utilization patterns during the 6-year interval between 1993 and 1999 appear to reflect very slow growth in the use of NDI among the medical community, contrary to concerns sometimes expressed by members of the news media that the use of high-technology imaging is a major factor in the increasing costs of health care. Use of individual imaging examinations by radiologists and nonradiologists will have to be compared to enable estimation of how much of the increase in utilization of NDI is related to self-referral.

	FOOTNOTES

 
Abbreviations: CMS = Centers for Medicare and Medicaid Services, HCPCS = Healthcare Common Procedure Coding System, NDI = noninvasive diagnostic imaging, RVU = relative value unit

Author contributions: Guarantors of integrity of entire study, all authors; study concepts, all authors; study design, D.C.L., L.P., V.M.R.; literature research, A.J.M.; data acquisition, J.H.S.; data analysis/interpretation, A.J.M., D.C.L., L.P.; statistical analysis, L.P.; manuscript preparation, A.J.M.; manuscript definition of intellectual content, all authors; manuscript editing, A.J.M., D.C.L., L.P.; manuscript revision/review and final version approval, all authors.

	REFERENCES

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5. Physicians’ current procedural terminology 4th ed Chicago, Ill: American Medical Association, 1998.
6. Healthcare Common Procedure Coding System (HCPCS). Centers for Medicare & Medicaid Services web site 2003. Available at: www.hcfa.gov/stats/anhcpcdl.htm. Accessed January 22.
7. Medicare managed care market penetration for all Medicare plan contractors: quarterly state/county data files. United States Health Care Financing Administration web site 2003. Available at: www.hcfa.gov/medicare/mpsct1.htm. Accessed January 22.
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11. An examination of procedures reimbursed under Medicare for breast disease and breast cancer, 1985 to 1996. April 7, 2000 2003. The National Breast Cancer Centre web site. Available at: www.nbcc.org.au/pages/info/resource/nbccpubs/medicare/results/mamm.htm. Accessed January 22.
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