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Renal Colic: Comparison of Use and Outcomes of Unenhanced Helical CT for Emergency Investigation in 1998 and 2002¹

¹ From the Departments of Medical Imaging (A.K., K.K., M.A.H.) and Emergency Medicine (S.L.), University of Toronto, University Health Network, Princess Margaret Hospital, 3-964, Toronto, ON, Canada M5G 2M9. Received May 17, 2004; revision requested August 3; revision received October 1; accepted November 4. Address correspondence to K.K. (e-mail: korosh.khalili{at}uhn.on.ca).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
PURPOSE: To determine retrospectively whether there had been any change between 1998 and 2002 in the use and outcome of computed tomography (CT) performed in the emergency department for patients presenting with symptoms of renal colic.

MATERIALS AND METHODS: Approval from the Research Ethics Board was obtained, and informed consent was waived. All CT examinations ordered from the emergency department of a tertiary care hospital and performed from July to December 1998 and July to December 2002 were identified. Reports were reviewed, and results were categorized as either (a) positive for urinary tract calculus disease (category I), (b) indicative of an alternate diagnosis (category II), or (c) negative for findings to account for the patient's symptoms (category III). The corresponding emergency department charts were reviewed for urine dipstick results for hematuria and for patient history of stone disease. For statistical analysis, ² testing and odds ratios were used.

RESULTS: During the 6-month period in 1998, 179 CT examinations were performed in patients who were admitted to the emergency department. During the same period in 2002, 234 CT examinations were performed. After correction for the total number of emergency department visits, it was determined that there was a relative increase of 21.3% (95% confidence interval: –0.0009, 0.47) in number of CT examinations performed in the emergency department. A total of 117 (65.4%) of 179 CT studies in 1998 and 153 (65.4%) of 234 CT studies in 2002 demonstrated renal calculus disease (category I), nine (5.0%) of 179 CT studies in 1998 and 17 (7.3%) of 234 CT studies in 2002 were used to identify an alternate diagnosis for patient symptoms (category II), and 53 (29.6%) of 179 CT studies in 1998 and 64 (27.4%) of 234 CT studies in 2002 were negative (category III). There were no significant differences between the rates of category I, II, or III results and the positivity rates for hematuria and urinary tract stone history during 1998 and 2002.

CONCLUSION: Despite a definite trend of increased CT use during 1998 and 2002, there was no significant decrease in the rates of positive renal colic results or alternate diagnoses.

© RSNA, 2005

	INTRODUCTION

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Renal colic is a common presenting symptom in hospital emergency departments. The lifetime incidence of nephrolithiasis is estimated at 12%, and the cost of this disease in the United States is estimated at $1.83 billion (1). Reports on the use of thin-section unenhanced helical computed tomography (CT) for the assessment of renal colic were first published in 1995 (2). Since then, thin-section unenhanced helical CT has been accepted as a rapid and accurate diagnostic test that essentially replaced other imaging modalities in most circumstances. CT has high sensitivity and specificity—estimated at 96%–97% and 96%–100%, respectively—for the detection of urinary tract stones (3–5). It also has the added ability to facilitate diagnosis of other conditions that mimic renal colic. The success of CT has resulted in widespread availability and acceptance by emergency physicians.

While the accuracy of thin-section, unenhanced helical CT versus other imaging modalities, such as intravenous urography, has been established (3–5), it is not clear how the use of CT has changed since CT became widely accepted for the imaging of patients with renal colic. Within our own practice, we had anecdotally noticed an increase in the number of CT examinations being ordered for renal colic. We wondered if such examinations were being used by referring clinicians as a screening tool given the ability of CT to facilitate diagnosis of alternate conditions. Such changes in the use of CT can markedly affect radiology workflow, budgets, and diagnostic decision algorithms. Thus, the purpose of our study was to determine retrospectively whether there had been any change in the rates of use and outcome of thin-section, unenhanced helical CT performed in the emergency department for patients presenting with symptoms of renal colic in 1998, when CT became widely available at our institution, and in 2002.

	MATERIALS AND METHODS

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CT Reports
Approval from the Research Ethics Board of our institution was obtained. Informed consent was waived. Reports of all CT examinations performed in patients presenting with symptoms of renal colic during two 6-month periods (July to December 1998 and July to December 2002) were ordered from the emergency department of a tertiary care teaching hospital and were accrued by one of the authors (A.K.). The same 6-month periods were used in each year to eliminate any effect of seasonal variation of renal stone disease, which has been described (6). For each study period, all CT examinations that were performed by using a renal colic protocol, which could be determined by examining the logbooks kept by CT technologists, were identified and cross-referenced with emergency department charts to ensure clinical assessment by an emergency physician. Data from multiple CT examinations performed in the same patient during each 6-month period were included only if (a) the examinations were performed during separate visits more than 30 days apart, (b) the emergency department chart suggested that each visit represented a new onset of renal colic, and (c) there was radiologic evidence that an obstructive stone detected during the first visit had been passed by the patient prior to returning to the emergency department. Only patients with a de novo episode of renal colic were included. Follow-up data, patients who were referred by urologists, and patients with prior urinary tract intervention were excluded. No intravenous pyelograms were obtained for the assessment of renal colic during either 6-month period. The total number of emergency department visits during these 6-month periods was recorded.

Imaging, Report Review, and Categorization of Results
All CT examinations were performed with the same protocol. Scanning parameters for the helical technique included a 5-mm section collimation reconstructed with 50% overlap and a pitch of 1.35–1.60. In 1998, scans were obtained by using a helical CT scanner (HiSpeed CT/I; GE Medical Systems, Milwaukee Wis) and, in 2002, scans were obtained by using a multi–detector row CT scanner (LightSpeed QX/I; GE Medical Systems). All scans were reviewed by one of the 16 board-certified radiologists specializing in abdominal imaging, including two of the authors (K.K., M.A.H.), or by seven abdominal imaging fellows. The radiologists had between 1 and 14 years of experience in radiology. In July 1998, a picture archiving and communication system was introduced at our institution, which ensured that all scans were monitored on dedicated workstations.

The CT reports were retrospectively reviewed by two of the authors in consensus (K.K., A.K.), and the presence or absence of a directly visualized urinary tract stone(s) was recorded. In addition, the presence or absence of CT evidence of urinary tract obstruction, such as hydronephrosis, hydroureter, perinephric stranding, and/or periureteric stranding (7), was recorded. Finally, any important incidental findings other than those related to urinary tract stone disease described in the CT report were recorded. Results for each patient were subsequently categorized as either (a) positive for urinary tract calculus disease (category I), (b) indicative of an alternate diagnosis (category II), and (c) negative for findings to account for the patient's symptoms (category III). These categories were further divided into one of seven subcategories labeled A–G (Table 1).

Emergency Department Chart Review
For each visit, the clinical emergency department charts that corresponded to each of the above CT examinations were requested from the health records department, and those that could be obtained were reviewed by one of the authors (A.K.) or by a research assistant. Two parameters (ie, the result of urine dipstick analysis for hematuria and the presence or absence of a personal history of urinary tract stone disease) were recorded from each emergency department chart for each of the two time periods. Urine dipstick results of 1+, 2+, 3+, or higher were considered positive; other results were considered negative.

Statistical Analysis
A ² test was used to compare the ratio of patients in category I in the two time periods. A normal-based confidence interval was constructed for the difference in proportions. A ² test was also used to compare the distribution of category I, II, and III results obtained during the two time periods. Commercially available software (S-Plus, version 6.1; Insightful, Seattle, Wash) was used for statistical analysis, and a P value of <.05 was considered to indicate a statistically significant difference.

The odds ratio was used to measure the overall strength of the relationship between the diagnosis of renal stone disease at CT and each of the two clinical markers (ie, the presence or absence of hematuria and history of urinary tract stone disease). The interactions between each of the two time periods and each of the two clinical markers, as well as the effect of the time period itself, were tested by using a logistic regression model. For this model, diagnosis at CT was used as the outcome to determine whether data for each of the two time periods could be combined and whether the relationship between renal stone disease and the two clinical markers changed between the two time periods. The use of clinical markers to identify patients with and those without urinary tract stone disease was assessed with the positive and negative likelihood ratios. Finally, the usefulness of both clinical markers combined was assessed first by calculating the percentage of positive CT results for each combination and then by calculating the likelihood ratio for each combination.

	RESULTS

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Emergency Department Visits and CT Examinations for Renal Colic
For the 6-month period of July to December 1998, a total of 20 739 patient visits to the emergency department were recorded. During these visits, 179 (0.863%) CT examinations were performed for new cases of renal colic in 176 patients. During the same 6-month period in 2002, 22 358 patient visits to the emergency department were recorded. During these visits, 234 (1.047%) CT examinations were performed for new cases of renal colic in 231 patients. Thus, from 1998 to 2002, there was a relative increase of 21.3% (95% confidence interval: –0.0009, 0.47) in number of CT examinations performed in the emergency department for patients presenting with symptoms of renal colic (Fig 1). The mean age of patients was 43.5 years in 1998 and 46.5 years in 2002. The proportion of male patients was 54.0% (95 of 176 patients) in 1998 and 58.0% (134 of 231 patients) in 2002. The differences in sex and in mean patient age were not statistically significant.

View larger version (20K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Bar graph demonstrates the number of CT examinations for renal colic (CTRCs) performed in the emergency department (ER) during 1998 and 2002 as a percentage of total emergency department visits.

Category II.—A total of nine (5.0%) of 179 CT studies in 1998 and 17 (7.3%) of 234 CT studies in 2002 were used to identify an alternate diagnosis for the patient's symptoms (category II). CT scans in four of nine patients in 1998 and five of 17 patients in 2002 demonstrated urinary tract causes for pain (subcategory D). The most common urinary tract cause was tumor (n = 4). CT scans in five of nine patients in 1998 and 12 of 17 patients in 2002 demonstrated nonurinary tract causes for pain (subcategory E). The most common nonurinary tract causes were diverticulitis (n = 4), cholecystitis (n = 3), pancreatitis (n = 3), and appendicitis (n = 2).

Category III.—A total of 53 (29.6%) of 179 CT studies in 1998 and 64 (27.4%) of 234 CT studies in 2002 were negative (category III). In addition, 15 (8.4%) CT scans in 1998 and 19 (8.1%) CT scans in 2002 demonstrated important incidental findings not related to the patient's pain. Of the scans that demonstrated incidental findings, nine (5.0%) of 179 in 1998 and 10 (4.3%) 234 in 2002 were also negative for urinary tract calculus disease (subcategory F). The most common and most important incidental findings were lymphadenopathy (n = 8), adnexal or inguinal masses (n = 4), liver masses (n = 4), and nonsimple renal cysts (n = 4). As shown in Figure 2, the distribution of category I, II, and III rates for each of the two 6-month time periods was similar (² = 1.17, P = .56).

View larger version (20K): [in this window] [in a new window] [Download PPT slide]   Figure 2. Pie charts demonstrate the distribution of CT results by category for 1998 and 2002 time periods. Positive = category I result, Alternate = category II result, and Negative = category III result.

The proportion of patients with a positive urine dipstick result was 108 (80.0%) of 135 in 1998 and 120 (73.2%) of 164 in 2002. The proportion of patients with a personal history of urinary tract stone disease was 52 (36.6%) of 142 in 1998 and 79 (42.0%) of 188 in 2002.

By using a multiple logistic regression model, we found that there was no significant variation in the results of urinalysis (P = .67) or in the number of patients with a history of urinary tract stone disease (P = .44) with respect to the year. The further lack of significant variation between the presence of urinary tract stone disease (category I) and year (P = .80) justifies combining the data from each of the two time periods for analysis of clinical markers. In this analysis, the odds of urinary tract stone disease (as determined at CT) were 2.6 times as high if the patient had a history of urinary tract stone disease (95% confidence interval: 1.6, 4.3) and 2.9 times as high if the patient had a positive urine dipstick result (95% confidence interval: 1.8, 4.9).

The overall prevalence of urinary stone disease (category I) was 65.4% among patients referred for CT. Among those who had both a positive urine dipstick result and a history of urinary tract stone disease, the prevalence of urinary tract stone disease, as determined at CT, increased to 79% (likelihood ratio, 2.15). A negative urine dipstick result and no history of urinary tract stone disease decreased the prevalence of urinary tract stone disease, as determined at CT, to 33% (likelihood ratio, 0.28).

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
The role of imaging in the management of acute renal colic has increased in recent years. This was noted first during the introduction of CT as an alternative to intravenous urography, ultrasonography (US), and radiography. Between 1997 and 1999, Gottlieb et al (8) noted a 26.7% increase in the use of all imaging modalities for the investigation of renal colic in the emergency department, predominantly as a result of the introduction of CT. Our results demonstrate a continued increase in the use of imaging, only now the increase is not because of a shift from one modality to another; rather, it is the result of a further increase in the use of CT.

Despite a definite trend of increased CT use (a 21.3% relative increase) during the 6-month study periods in 2002 and 1998, there was no decrease in the rate positive renal colic results or alternate diagnoses. There was also no decrease in the rate of positive urinalysis results or positive history of urinary tract stone disease. It appears that, in 2002, our emergency department physicians did not use CT to screen patients for other diseases any more than they did in 1998. Instead, our results suggest that, in 2002, clinicians were more likely to use CT to image patients with true renal stone disease than they were in 1998.

The increased tendency to image patients suspected of having renal colic may be the result of the relative ease of use and speed of CT compared with that of intravenous urography or US and radiography combined. This increase may also represent a response to the increasing volume of patient visits to our emergency department. There were 1619 more patient visits to our emergency department in 2002 than in 1998, a 7.8% increase. The ease of use, accuracy, and availability of CT, along with this increasing volume, may be responsible for increased use of imaging in patients who present with symptoms of renal colic. This has implications regarding health policy and economic decisions. Whether the increased use of CT can be justified depends on whether all patients with classic symptoms of renal colic, as well as a positive urinalysis result and/or family history of urinary tract stone disease, require imaging at the time of presentation. The answer may vary depending on regional clinical practices and medicolegal environments. It is important to note that, at our institution, all CT consultations from the emergency department are screened and approved by a radiology resident, fellow, or attending physician. The contribution of this additional input toward limiting the use of imaging to only those patients with a valid indication of renal colic is unknown.

The prevalence of renal stone disease in the population of patients referred for CT in this study (65.4%) is consistent with the rates of positive findings quoted in previous reports (8–12). In addition, the rates of alternate diagnoses for the patients' acute pain in this study (5.0% in 1998 and 7.3% in 2002) are consistent with those quoted in previous reports (8–12). Table 3 summarizes the data from these studies.

There are alternate explanations of our results indicating no change in the CT positivity rates for renal stone disease despite the increased use of CT. The improved detection rates of disease in 2002 compared with those in 1998 could explain the lack of a decrease in positivity rates on the basis of better recognition of primary and secondary CT findings of urinary tract stone disease. We believe, however, that this is unlikely because CT examinations for renal colic were used in our department for 3 years prior to 1998; the great majority of these cases were reviewed by staff abdominal radiologists, and diagnosis of the disease is relatively simple. By 1998, intravenous pyelography had been abandoned for the assessment of acute renal colic in the emergency department, but it is possible that more patients were imaged by using radiography and US in 1998 than in 2002. Radiography and US, however, have not been routinely used in our practice in the emergency setting; therefore, the contribution of these modalities would likely be negligible. Finally, an increase in the incidence of the disease in the population may account for the steady rates of positivity. This, however, would require a considerable and unlikely change in the population being served by our institution during the relatively short study period. There were no hospital closures in the vicinity of our institution to result in such a shift.

The review of emergency department charts also shows that two commonly used clinical markers obtained during the emergency department work-up of patients—that is, patient history of urinary tract stone disease and urine dipstick results—do not have a high enough negative predictive value to obviate imaging. When both results were negative, 33% of patients with renal colic had positive results at CT. When both were positive, however, 79% of patients with renal colic had positive results at CT. These two parameters alone are thus poor predictors of renal colic as an outcome measure and do not sufficiently alter the probability of urinary tract stone disease, a finding previously reported in the literature (11).

An important limitation of this study was the large number of CT interpreters and our inability to control for or critically evaluate their experience. While a large number of interpreters decreases the possibility of a systematic bias, it could be argued that a higher experience level may have led to the maintenance of the similar rates of positivity. We limited our patients to those who had undergone CT or intravenous urography; we do not know the proportion of patients suspected of having renal colic who did not undergo imaging. Therefore, caution needs to be used in extrapolating our results to all patients who may present to the emergency department with symptoms of renal colic. We could not determine what other imaging modalites apart from intravenous urography (eg, radiography and US) were used to evaluate patients with renal colic. Finally, only a portion of the emergency department charts (79.3% in 1998 and 80.3% in 2002) were found and reviewed. We did not determine the reason for the lack of retrieval of the other charts according to medical records. Therefore, we cannot exclude a bias owing to a systematic cause of inaccessibility of the charts.

In conclusion, our study demonstrates that, although emergency department physicians at our institution were imaging more patients by using CT in 2002 than in 1998, they were just as likely to be correct in their diagnosis during either time period. The most likely explanation is that a greater number of patients with true renal colic are imaged today than in the past.

	ACKNOWLEDGMENTS

 
The authors thank George Tomlinson, PhD, for his valuable statistical analysis support and Melanie Crozier, MD, for assisting in data collection.

	FOOTNOTES

 
Authors stated no financial relationship to disclose.

Author contributions: Guarantor of integrity of entire study, K.K.; study concepts, A.K., K.K.; study design, A.K., K.K., S.L.; literature research, A.K.; data acquisition and analysis/interpretation, all authors; statistical analysis, A.K., K.K.; manuscript preparation and definition of intellectual content, A.K., K.K.; manuscript editing, all authors; manuscript revision/review and final version approval, A.K., K.K.

	References

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