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Health Policy and Practice |
1 From the Department of Radiology, Stanford University School of Medicine, Stanford, CA 94305-5105. Received February 26, 1999; revision requested May 5; revision received August 18; accepted September 24. Supported in part by GE-AUR Radiology Research Fellowship; National Institutes of Health grants R01HL50305, 1P41-RR09784, and LM07033; the Lucas Foundation; and the Phil N. Allen Trust. Address reprint requests to G.D.R. (e-mail: grubin@stanford.edu).
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Abstract |
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 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: A single observer determined the variable direct costs of performing nine intraarterial DSA and 10 CT angiographic examinations in age- and general health–matched patients with AAA by using time and motion analyses. All personnel directly involved in the cases were tracked, and the involvement times were recorded to the nearest minute. All material items used during the procedures were recorded. The cost of labor was determined from personnel reimbursement data, and the cost of materials, from vendor pricing. The variable direct costs of laboratory tests and using the ambulatory treatment unit for postprocedural monitoring, as well as all fixed direct costs, were assessed from hospital accounting records. The total costs were determined for each procedure and compared by using the Student t test and calculating the CIs.
RESULTS: The mean total direct cost of intraarterial DSA (± SD) was $1,052 ± 71, and that of CT angiography was $300 ± 30, which are significantly different (P < 4.1 x 10-11). With 95% confidence, intraarterial DSA cost 3.2–3.7 times more than CT angiography for the assessment of AAA.
CONCLUSION: Assuming equal diagnostic utility and procedure-related morbidity, institutions may have substantial cost savings whenever CT angiography can replace intraarterial DSA for imaging AAAs.
Index terms: Aneurysm, aortic, 981.73 • Computed tomography (CT), angiography, 981.12912, 981.12916 • Cost-effectiveness • Digital subtraction angiography, comparative studies, 981.122
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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One advantage of CT angiography relative to intraarterial DSA is the use of a peripheral intravenous injection of iodinated contrast material compared with the direct arterial injection required in intraarterial DSA. This has a substantial effect on the patient in terms of diminished patient morbidity by eliminating intraarterial catheterization and substantially reducing the duration of the procedure and the required postprocedural bed rest. A CT angiographic examination typically requires 30 minutes of patient involvement, after which the patient is free to return to normal daily activities. DSA, on the other hand, typically requires 8–24 hours for the procedure and postprocedural bed rest, to ensure hemostasis.
Another important advantage of CT angiography is that the volumetric data acquired enable the acquisition of views from any angle and perspective; thus, this modality is free of the limitations of overlap and parallax that plague intraarterial DSA. As a result, there have been reports of reduced diagnostic accuracy with intraarterial DSA relative to that with CT angiography in characterizing the neck of AAA, identifying accessory renal arteries, and characterizing renal arterial stenoses (10–12). Furthermore, we have observed a dramatic and sustained shift in practice patterns at our institution during the past 5 years, with a substantial reduction in requests for diagnostic DSA in favor of CT angiography for the preoperative assessment of AAA. It has been suggested that CT angiography not only provides equally or more useful information than does intraarterial DSA for some applications, but it also is less expensive. However, to our knowledge, the relative costs of performing CT angiography and intraarterial DSA had not been quantified before this study. Our goal was to determine the relative cost, from the perspective of the medical center, of using CT angiography versus intraarterial DSA for the preoperative assessment of AAA.
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The patients who underwent both CT angiography and intraarterial DSA were enrolled in a clinical trial of endovascular stent-grafts that required the acquisition of both types of images. The referring physician selected the type of imaging study for the other 13 patients. This selection process occurred independently of the patients' involvement in our study. Our study did not influence the type of imaging, and the nonemergency cases were recruited as consecutively as possible without exclusion criteria. Some patients required additional evaluations such as run-off studies concurrent with aortic angiography. The costs for materials and labor and the other costs incurred during these additional evaluations were carefully excluded from our study data.
All patients had a comparable general health status and were ambulatory and able to accurately answer questions about their past medical history. All procedures were performed on an outpatient basis. The patients' medical records, including all laboratory studies indicating renal function, were retrospectively reviewed for any substantial coexistent morbidities, including pulmonary disease, cardiac disease, liver disease, renal disease, diabetes mellitus, or gout. Eight of the nine patients who underwent intraarterial DSA had one substantial coexistent morbidity, and eight of the ten patients who underwent CT angiography had one substantial coexistent morbidity. The remaining three patients had no substantial coexistent morbidity.
One patient in the intraarterial DSA group who was initially recruited for analysis was later excluded because of failure to meet the selection criterion of being an ambulatory outpatient. Another patient in the intraarterial DSA group reported a possible allergic reaction to contrast material, but the details were vague. In this case, the radiologist decided to minimize the patient's exposure to contrast material by using carbon dioxide in the acquisition of some of the images. The patient had no adverse reaction to the contrast material and has since undergone two CT examinations with iodinated contrast material without any difficulties.
Imaging Procedures
CT angiography.—The temporal progression of a CT angiography procedure is illustrated in Figure 1. For each patient, the procedure began when the patient arrived in the CT suite. The patient was positioned on the CT table by a CT technologist, and a scout projection was obtained. Intravenous access was achieved by a registered nurse and was connected to a power injector (Medrad, Indianola, Pa) filled with low-osmolar iodinated contrast material (Omnipaque 300; Nycomed-Amersham, Princeton, NJ). Three types of CT scans were subsequently acquired: (a) preliminary 10-mm-collimation helical CT scans to localize the anatomy of interest, (b) sequential, single-level CT scans to measure contrast material circulation time, and (c) a CT angiogram, which was acquired in a single scan with 3- and 5-mm collimation and intravenously administered contrast material.
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A dedicated 3D technologist trained in CT and 3D rendering created two orthogonal, curved planar reformations through the aorta and all renal, mesenteric, and iliac arteries and generated shaded surface displays from the unedited data. The technologist then removed the bones from the CT data by using a combination of 3D region-of-interest and 3D region growing editing. Shaded surface display and maximum intensity projection images were created from the edited CT data. Laboratory tests were not ordered either in anticipation or as a result of CT angiographic results.
Intraarterial DSA.—The temporal progression of an intraarterial DSA procedure is illustrated in Figure 2. Each patient arrived at the ATU for completion of paperwork, bed assignment, and establishment of intravenous access. Blood was drawn for laboratory tests if this was ordered by the attending radiologist or radiology fellow. Six patients in our study underwent laboratory blood testing as follows: six patients were tested for blood urea nitrogen and creatinine levels; four, for prothrombin and/or partial prothrombin times; two, for complete blood cell count; two, for electrolyte levels; and one, for serum glucose level.
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The patient was transported back to the ATU and remained there until he or she was approved for discharge by a radiologist. Admission to the ATU did not constitute a hospital admission, and thus outpatient status was maintained throughout the angiographic protocol.
Because our medical center serves as both a university hospital and community hospital, the intraarterial DSA procedures were performed by either university radiologists or private radiologists. A team of two university radiologists (one fellow and one faculty) performed intraarterial DSA in three of the nine cases, and a single private radiologist performed intraarterial DSA in six of the nine cases. The university faculty radiologists had 9–15 years of angiographic experience, and the private radiologist was a full-time angiographer with 20 years of angiographic experience.
Definition of Costs
Costs were categorized as either variable direct, fixed direct, or indirect, according to the classifications used by our medical center's cost accounting department. Variable costs are those that vary, depending on the procedure—for example, the costs for the amount of contrast material used and the technologist labor. Fixed costs are those that do not change with the procedure—for example, the costs for receptionist labor and equipment depreciation. Direct costs are those associated with the performance of the procedure, regardless of whether they vary—for example, the costs for contrast material use, cleaning, and maintenance of scrub clothing.
Indirect costs are those incurred independently of the procedure and include expenses for grounds (eg, parking lot, cafeteria, walkways, and gardens) and maintenance, general depreciation, insurance, security, materials management, general administration, human resources, utilities, and housekeeping. Because indirect costs are incurred regardless of the procedure performed, they do not reflect the cost of choosing one procedure over the other. For this reason, indirect costs were excluded from this cost analysis.
For this study, variable direct costs included those for all materials and labor directly attributable to the performance of the procedures. Fixed direct costs included those for equipment depreciation, maintenance and service, administrative and support personnel (including receptionists and chief technologists), apparel, telephones, and supplies.
Measurement of Costs
Variable direct costs.—All variable direct costs were tracked by the same investigator (M.D.A.) for all patient studies, from the time the patient arrived in the ATU for intraarterial DSA and/or in the CT suite for CT angiography until the initiation of patient transport from the angiography suite to the ATU for intraarterial DSA and/or the completion of 3D rendering for CT angiography. All materials used in connection with the procedure were recorded, and their costs were assigned by the medical center purchasing department as the actual prices paid by the medical center.
Labor was tracked by using time and motion analyses; the amount of time each laborer spent on a case was recorded to the nearest minute. When a laborer was working on more than one case simultaneously, the proportion of time dedicated to the case being tracked was estimated. Laborers included all physicians, nurses, and technologists involved in the procedure. For salaried workers, their costs were apportioned on the basis of their total annual compensation, including salary and benefits, divided by their estimated number of billable work hours per year. Neither the personnel not directly participating in the procedure nor the personnel caring for the patient before and after the procedure were tracked by using time and motion analyses. This group included personnel in the ATU, whose costs were accounted for separately as ATU direct costs, and other nontracked personnel such as receptionists and schedulers, whose costs were accounted for in the fixed direct costs. The time for interpreting the imaging studies by the radiologists was not measured because resident and fellow teaching during read-out confounded this measure. As a result, the measurements reflected the labor costs associated with performing the procedure and not those associated with image interpretation.
Fixed direct costs.—The specific allocation of fixed direct costs was dictated by guidelines from a 1991 publication from the California Office of Statewide Health Planning and Development, the Accounting and Reporting Manual for California Hospitals (13). All fixed direct costs, as well as all variable direct costs for the ATU, were determined from our medical center's accounting system (Transition System I [TSI]; Transition Systems, Boston, Mass). With this system, medical procedures were defined as "products," which were assigned relative value units by a team of financial analysts and medical personnel to apportion expenses to products on the basis of resource utilization. The TSI apportioned fixed direct costs to each product on the basis of utilization, relative value units, and the total costs incurred during the measurement period, as reported by our payroll and materials management departments. To our knowledge, the TSI accounting data are the most accurate measure of fixed direct costs. Although this system is routinely used to apportion both variable and fixed charges, for this study we used it to assign fixed costs only and relied on data from time and motion labor analyses and individual materials accounting as more definitive indicators of variable costs.
Fixed direct costs are divided among all procedures that use a given set of equipment and facilities. In a very busy department, for example, the fixed direct cost per procedure will be relatively low. Because utilization affects fixed direct cost allocation, we reviewed our institution's 1997 MECON-PEERx report (MECON, San Ramon, Calif) to compare the level of utilization in the CT and intraarterial DSA suites. MECON is a widely used benchmarking company that provides financial and performance comparisons between hospitals. In the MECON-PEERx report, similar hospitals are compared by using a wide variety of performance figures. Our institution is compared to a nationwide group of university hospitals.
The MECON-PEERx report provides a benchmark of "procedures per room per day" used in both the CT and catheter-angiography suites. This benchmark is perhaps the best measure of study volume and equipment utilization in a department. A higher percentile score indicates higher volume and utilization compared with those of other institutions. With this benchmark, our CT department scored at about the 68th percentile, and our catheter-angiography department scored at about the 79th percentile. These figures are in the same quartile, which indicates that utilization was about the same in the two departments at the time of this study. These figures are also near the median, which indicates that the volumes of cases in our CT and catheter-angiography departments were similar to those at other university hospitals.
The total fixed direct costs of CT angiography were defined by the sum of fixed direct costs for two TSI products—CT of the abdomen with and without contrast material and CT intravenous line setup. All patients were assigned the same value for fixed direct costs. The total fixed direct costs for intraarterial DSA were based on a combination of three TSI products—"aortography, Abd, S&I" ("aortography, abdominal, superior and inferior"), "rad treatment rm 1 HR" ("radiology treatment room, 1 hour"), and "rad treatment rm 0.5 HR" ("radiology treatment room, 0.5 hour"). All patients who underwent intraarterial DSA were assigned the cost of "aortography, Abd, S&I." In addition, each patient was assigned an appropriate combination of the other two products, depending on how long the procedure room was used.
Because time and motion analyses could not be practically performed in the ATU, both variable and fixed direct ATU costs were calculated by using the TSI. The specific products billed to each patient by the nursing staff were recorded and reviewed with the ATU nurse manager for consistency. All direct laboratory costs were determined by using the appropriate sums of TSI product costs.
Statistical Analysis
Total direct costs (variable and fixed) were tabulated for the procedural, ATU, and laboratory portions of each examination, with further subdivision of the procedural costs into variable direct components from labor, supplies, and contrast material. The mean and SD for each cost category were calculated among the patients for CT angiography and intraarterial DSA. The costs of intraarterial DSA performed by university versus community radiologists also were compared. Ninety-five percent CIs were calculated for the total costs by using bootstrap bias corrected and accelerated intervals (14).
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The cost of personnel for intraarterial DSA was 2.87 times greater than that for CT angiography, predominately because of the requirement for nursing and physician involvement during intraarterial DSA. A community attending radiologist without house staff performed six procedures, and a university attending radiologist with the assistance of interventional radiology fellows performed three procedures. Residents did not participate in the performance of any of the intraarterial DSA procedures. There was no statistically significant difference in personnel costs between intraarterial DSA performed by university radiologists and that performed by community radiologists. Although supplies accounted for only 15% and 3% of the costs for intraarterial DSA and CT angiography, respectively, the supply costs for intraarterial DSA were 17.9 times greater than those for CT angiography. The breakdowns of costs for supplies and personnel utilization for intraarterial DSA and CT angiography are summarized in Tables 2–4.
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The fixed direct costs for intraarterial DSA were 52% greater than those for CT angiography. ATU and laboratory costs together composed 39% of the costs for intraarterial DSA, but these services were not used for CT angiography.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Because this cost-accounting fact might seem to skew the measured intraarterial DSA costs toward a higher value, we broke down the time each patient spent in preparation, during the procedure, and in postprocedural monitoring and care. The variability in preprocedural preparation can be attributed primarily to angiography suite and attending physician availability after the patient's admission into the ATU. Postprocedural monitoring also was variable, ranging between 7.2 and 27.2 hours (mean, 12.7 hours). Three patients required more than 8 hours of postprocedural care—14.3, 26.6, and 27.2 hours. The rationale for these extended stays were, respectively, late procedural completion, which resulted in an overnight stay; wound site complications; and incisional pain, spasms, acute confusion, and agitation. Because the types of wound site complications were not clearly stated in the medical record, their nature and severity remain unclear. The patient with incisional pain and spasms had a charted history of dementia, which may have contributed to the development of these complications.
When we summed the above times to determine the total time that an ATU bed needed to be reserved for or occupied by a patient, the mean total amount of time was 16.0 hours ± 8.1. Procedural times were included in this calculation because of the uncertainty as to when the patient was likely to return to the bed after the procedure and thus the uncertainty of the need to reserve the bed and staffing for the patient's return. When our fixed direct cost calculations were revised on the basis of the actual time that ATU beds were occupied, the mean total direct costs of intraarterial DSA decreased to $943.61 ± 143.31. The 95% CI for intraarterial DSA costs became $854.78–$1,032.43, which, on the basis of the values presented in Table 1, is 2.84–3.44 times greater than that for CT angiography.
Although the mean cost of contrast material for intraarterial DSA was not substantially different from that for CT angiography, the contrast material expense represented a substantially greater percentage of the cost of performing CT angiography (40%) compared with that of performing intraarterial DSA (12%). At the time of our data collection in 1997, the mean cost of nonionic contrast material was $1.95 per gram of iodine. As of April 1998, this value had decreased to $1.04 per gram of iodine. Of all the variable costs incurred when performing intraarterial DSA and CT angiography, those for nonionic contrast material were the only expenses that had substantially changed during the year following data collection. Because contrast material costs represent a substantially greater percentage of the total cost of CT angiography, the decrease in contrast material costs had a greater influence on the overall cost of CT angiography compared with that of intraarterial DSA. In fact, when we recalculated the total costs on the basis of the 1998 nonionic contrast material costs, the mean contrast material costs were reduced to $63.41 ± 29.65 and $63.33 ± 12.86, respectively, and represented 6% and 21%, respectively, of the total costs for intraarterial DSA and CT angiography. The total direct costs were reduced to $987.90 and $244.83, respectively, for intraarterial DSA and CT angiography. Consequently, the cost of intraarterial DSA increased to 4.04 times that of CT angiography. As contrast material costs continue to decrease, the disparity between CT angiography and intraarterial DSA costs will further widen.
An intriguing result of this analysis was the discrepancy in laboratory test costs between intraarterial DSA and CT angiography. Because both of these examinations require the use of iodinated contrast material, one might expect that similar laboratory tests would be required for the two imaging studies. We reconciled this result by recognizing that the amount of contrast material to be used during DSA is less predictable than that during CT because intraarterial DSA is an invasive procedure in which the radiologist cannot always predict what problems may arise or what interventions might become necessary in even the simplest of cases. Our policy regarding creatinine levels in outpatients undergoing contrast material–enhanced CT is to check any previous creatinine levels on record in our laboratory. If none are present and the patient does not have diabetes, gout, or multiple myeloma, then we assume adequate renal function and proceed without checking the serum creatinine level.
Cost-effectiveness and cost-benefit studies are appearing more frequently in the medical literature, but the prevalence of rigorous investigative methods to support these analyses for imaging studies is disturbingly low (15). We chose to perform a cost-identification analysis in which equivalent outcomes of the diagnostic strategies were assumed (16). Although we did not specifically examine patient outcomes in this study, the findings described in the official radiology reports for each examination corroborated with the surgical findings for all patients who underwent surgical repair of AAA. Nevertheless, because the results of the first of the two imaging studies were not blinded from the radiologists who performed the second of the two procedures in the three patients who underwent both imaging examinations, and because the sample size of this study was only 10 for CT and nine for DSA, reliable conclusions about the efficacy of these two procedures for planning AAA repair cannot be ascertained from these data.
Although many authors (15,17) base cost analyses on charge data, preferring a "societal perspective" to cost accounting, we chose to define costs from the perspective of the medical center (18). Because discounted fee for service and managed care have become the predominant economic models for reimbursing health care expenses in the United States, health care providers must understand their costs of performing procedures to maintain adequate net revenues. This is particularly true with capitation, in which health care providers must bear the full burden of expenses without a possibility of recovering additional revenues over the prepaid premiums when the costs are not met. The advantages to the patient that result from undergoing either CT angiography or DSA, such as diminished discomfort and reduced time from work, were not studied because they are not incurred costs to the medical center.
To our knowledge, this is the first published time and motion analyses of variable direct costs associated with medical imaging procedures, and it provides a level of rigor that eliminates the assumptions inherent in charge-based (17,19–22), relative value unit–based (23–25), ratio of costs to charges (25–31), and estimated cost measurement (31–34) analyses. Substantial differences in the reported magnitude of relative CT and conventional angiography costs can be found, depending on the method of cost accounting (20,30,33,34). Fixed direct costs, which, on the basis of our hospital's cost accounting system, comprised all costs generated in the ATU, were analyzed by using the TSI, which assigns uniform costs to intermediate products. These products are used annually to calculate the product volumes for determining relative value units, which are then used to apportion direct and indirect costs. This system has been described fully by other investigators (26,32).
Our analysis had limitations. There were no costs from complications related to the 19 procedures performed in this study. A substantially larger sample size probably would have resulted in added costs for treating complications related to the intravascular injection of iodinated contrast material and the arterial catheterization. Although serious complications are rare, because of the invasive nature of intraarterial DSA, it is likely to result in a greater prevalence of procedural complications than is CT angiography; this further broadens the disparity in costs. As a result of the absence of complications or other sources of long-term costs from these procedures, the discounting of future costs was excluded from our analysis; this was done to satisfy the rigors of Blackmore and Magid's principles for the presentation of cost data (15). Although 10 CT angiographic and nine intraarterial DSA examinations might seem to be a small number of studies to track, there was little variability in the total cost among individual cases for each procedure, a fact reflected in the narrow 95% CIs.
Another limitation of our study was that the data were collected from only one institution, unlike in other well-conceived analyses, in which data from multiple institutions were considered (29). However, our medical center serves as both an academic training center staffed by residents and fellows and a community medical center in which angiographic procedures are performed exclusively by private radiologists. This setting provided an opportunity to assess differences between community- and university-based practices of angiography. At our institution, cross-sectional imaging, specifically CT angiography, is performed exclusively by university radiologists. When analyzing personnel utilization for intraarterial DSA, we were surprised to find that there were no substantial differences in total personnel costs or technologist and nursing costs between university and community services (Table 2). Because our university service is radiology fellow driven, and residents did not participate in any of the procedures in this study, we do not know the effect of junior house staff involvement on procedure duration and personnel costs.
Furthermore, all costs, but particularly those for labor, are undoubtedly biased by regional standards and volume discounts. As a result, the absolute amounts reported herein might vary, but the relative costs should be generalizable to institutions throughout the United States.
A dedicated 3D laboratory technologist is not available at most institutions. We justified the employment of this individual in October 1996 on the basis of a volume of 60 3D processing cases each month in our radiology department at the time of this study. Our volume subsequently increased to 120–140 cases per month in 1998, necessitating the hiring of a second full-time, dedicated 3D technologist. Although in some practices, physicians may perform the 3D processing, particularly at sites with low volumes of 3D studies, our experience since 1993 suggests that appropriately trained CT and MR technologists can perform 3D processing adequately. Our data reflect the relative costs of performing CT angiography at a site where the volume of 3D studies supports the employment of technical personnel to perform 3D processing, at least on a part-time basis.
Finally, several important costs associated with CT angiography and intraarterial DSA—specifically, indirect and interpretation costs—were not quantified in this study. Indirect costs, which account for the expenses of running a medical center but cannot be specifically attributed to an examination or procedure, are apportioned somewhat arbitrarily and therefore were not included in our analysis. Nevertheless, variations in the indirect costs of a major medical center versus those of a free-standing imaging center can be substantial and affect the overall but not relative costs of performing procedures. Three noteworthy indirect costs are those for future capital improvements, acquiring and maintaining adequate monetary reserves, and treatment of uninsured and underinsured patients. Professional costs beyond those attributable to the procedure itself—namely, interpretation—were not included in this analysis, primarily owing to the difficulties of separating interpretation from teaching in an academic medical center. However, the costs of interpretation for CT angiography and intraarterial DSA are likely to be similar when experienced readers are interpreting the studies. Additional professional costs, such as those for imaging protocol development and technologist training, also were not included for similar reasons. As a result, the absolute values measured served only in calculating the relative direct costs and did not represent the total examination costs.
In summary, in our experience, the direct costs of performing CT angiography for the preoperative assessment of AAA were 3.5 times lower than those of performing intraarterial DSA in the first quarter of 1997 and 4.0 times lower when recent reductions in the cost of low-osmolar contrast material were considered. Given the likelihood that CT angiography offers greater diagnostic utility than does intraarterial DSA for the assessment of AAA and the lower morbidity associated with CT angiography, the substantial cost reduction achieved by performing CT angiography should provide further justification for its replacement of intraarterial DSA for AAA imaging.
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Acknowledgments |
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Footnotes |
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Abbreviations: AAA = abdominal aortic aneurysm ATU = ambulatory treatment unit DSA = digital subtraction angiography TSI = Transition System I 3D = three-dimensional
Author contributions: Guarantors of integrity of entire study, G.D.R., M.D.A.; study concepts, G.D.R.; study design, all authors; definition of intellectual content, G.D.R., M.D.A.; literature research, G.D.R.; clinical studies, M.D.A.; data acquisition, M.D.A.; data and statistical analyses, G.D.R., M.D.A.; manuscript preparation, G.D.R., M.D.A.; manuscript editing, G.D.R.; manuscript review, M.D.A., S.N., M.D.D.
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