First published online August 6, 2007
British Journal of Radiology (2007) 80, 617-624
© 2007 British Institute of Radiology
doi: 10.1259/bjr/78311002
Bowel preparation for excretory urography is not necessary: a randomized trial
M Jansson, MD
H Geijer, MD, PhD, BA
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T Andersson, MD, PhD
Department of Radiology, Örebro University Hospital, SE-701 85 Örebro, Sweden
Correspondence: Dr Margareta Jansson, Universitessjukhuset Örebro, Örebro 701 85, Sweden. E-mail: margareta.jansson3{at}orebroll.se
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Abstract
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Despite the fact that computed tomography is becoming more commonly used to investigate the genitourinary tract, intravenous urography still plays an important role in uroradiology. The aim of this study was to compare bowel purgation and two other preparation methods — dietary restrictions and no preparations at all — in an attempt to find the optimal procedure for uniform practice. 210 consecutive patients were randomised to three preparation groups with 70 in each group. Group 1 received standard bowel purgation, Group 2 was instructed to fast, while Group 3 had no preparation at all. Irrespective of preparation, all patients underwent the same examination procedure. The examining radiographer and evaluating radiologists were unaware of the type of preparation given. Image quality was assessed according to European Commission criteria for excretory urography. The effectiveness of bowel purgation and the amount of residual gas were scored separately. There was no statistically significant difference in the proportions with fulfilled criteria between preparation Groups 1 and 2 and Groups 1 and 3. A criterion was regarded as fulfilled only when all three observers agreed. Assessment of the amount of residual faeces proved the effectiveness of our standard bowel purgation. The results of our study show equality of the evaluated preparation methods and cannot justify further use of bowel purgation before excretory urography.
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Introduction
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Despite the fact that CT is becoming more common in investigation of the genitourinary tract, intravenous urography still has an important role in uroradiology. Since urography became established for evaluation of the morphology and pathology of the urinary tract, it has generally been considered that bowel gas and faeces overlying the kidneys obscure details on the image. It has therefore been concluded that bowel purgation will improve the visibility of the urinary tract details and thereby the image quality. Despite the growing evidence [1–5] questioning the value of prior bowel purgation, this procedure remains prevalent in many radiological departments. In fact, it is one of the preparation standards next to dietary restrictions and no preparation at all. Among authors of radiological and urological textbooks, there is disagreement about preparation recommendations. Whereas some of them have abandoned bowel purgation [6, 7], others still recommend bowel purgation as a routine, in case of unavailable tomography or to visualize small or faintly calcified stones [8]. Since those recommendations were formulated, some of the examination conditions have changed. The present use of low osmolar intravenous contrast media, modern digital radiography, effective abdominal compression and nephrotomography greatly improves the visibility of urinary tract details. Since the latest study [5] was reported in 1996, the European Commission has laid down the image quality criteria for radiographic examinations [9], and digital radiography has almost completely replaced conventional radiography. Digital imaging has introduced new ways of image evaluation with possibilities of grayscale and contrast alteration.
The aim of this study was to compare three methods of preparation for excretory urography: bowel purgation together with dietary restrictions (a method used as a standard at many hospitals in Sweden), dietary restriction alone and no preparation at all.
We designed a randomized controlled trial to demonstrate the equality of these three preparation methods if this exists. The image quality assessed according to European Commission criteria for excretory urography was our primary outcome. As quality parameters of administered bowel purgation and/or of patient compliance, we assessed the amounts of residual faeces and gas, which were secondary outcomes of this study.
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Methods and materials
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Participants
The study comprised consecutive ambulatory patients older than 15 years who were referred for excretory urography. Exclusion criteria were contraindications to laxatives, such as small bowel stoma, colostomy and previous colon resection.
The study was approved by the local ethics committee. All patients who gave their informed consent were randomly assigned to one of three preparation methods.
Intervention
The first group (Group 1) received our standard preparation consisting of 2 l of polyethylene glycol electrolyte solution (LaxabonTM; AstraZeneca, Mölndal, Sweden). The patients were instructed to fast for 4 h before starting the laxative treatment and to drink the laxative solution in the afternoon the day before the examination. The second group (Group 2) was instructed to fast for 12 h before the examination, and Group 3 had no preparation at all. Irrespective of preparation, all patients underwent the same examination procedure. The examining radiographer was unaware of the patients' preparation group.
Initial survey images of the abdomen were obtained, after which the contrast medium iohexol 300 mg ml–1 (Omnipaque, GE Healthcare, Stockholm, Sweden) was administered intravenously. The dose was 40 ml in all patients weighing under 80 kg and 50 ml in those weighing above 80 kg. Standard nephrographic and pyelographic effect images were then obtained, first with and then without ureteral compression. The exact examination technique is described in Table 1
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Objectives and sample size
The study was planned as an equivalence study with power calculation based on a pilot study. Traditionally, when comparing two treatments, the aim is to prove that their effects are different. In equivalence studies, however, instead of rejecting the null hypothesis, the aim is to prove that it is true. The null hypothesis in the present study was that the tested preparations and standard bowel purgation assessed according to European Commission image quality criteria are equivalent in image quality. Equivalency was defined as a difference not larger than 0.5 points in European Commission score where the maximum score was 9. The sample size was based on power analysis with the power set to 90% at a 5% significance level. This resulted in 44 participants per group, a total of approximately 150 patients.
Randomization
Randomization was performed according to the CONSORT (Consolidated Standards of Reporting Trials) statement [10]. Blocked randomization was used. 232 consecutive out-patients were asked to participate in the study, and those who gave their consent received a letter with preparation instructions.
Radiographs
The images were obtained with a flat panel detector (Trixell Pixium 4600; Thales Electron Devices, Vélizy, France) mounted in a bucky table (Digital Diagnost; Philips Medical Systems, Best, the Netherlands) and integrated into a picture archiving and communication system (PACS; Sectra IMTEC AB, Linköping, Sweden).
Image quality
The primary end point was image quality assessed according to the European Commission criteria for excretory urography [9]. The criteria are listed in Table 2. Three radiologists unaware of the preparation method evaluated all images independently. A fulfilled criterion was counted as 1 and non-fulfilled as 0.
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Table 2. Image quality criteria according to the European Commission guidelines for evaluation of diagnostic radiographic images used in this study
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Fo,i,c = fulfilment of criterion c for image i and observer o.
O = number of observers.
I = number of images.
C = number of criteria.
The definition implies that the image criterion score (ICS) can be used as a score for individual images, criteria and observers.
As a quality control of administered bowel purgation and/or patient compliance, we assessed the images with regard to residual amounts of faeces and gas. Among patients who were attending our department for excretory urography, we chose one patient prepared with our ordinary bowel purgation and who was not included in this study as a reference. This patient had some amounts of gas and faeces, as shown in Figure 1. All examinations were compared with this reference examination. The abdominal area was divided into four quadrants with the midline and a transverse line at the level of the third lumbar vertebra. The examinations were assessed separately concerning gas and residual faeces. A three-grade score was used: 1, worse than reference; 2, equal to reference; and 3, better than reference. Three radiologists unaware of the patient's preparation group assessed all images independently.
All images were evaluated on the same type of monitor (MultiSync LCD1880SX; NEC, Tokyo, Japan) in order to avoid variations. Zooming and alteration of the grayscale were allowed.
Statistical methods
Intention to treat analysis of assessments was performed, using the t-test for comparison between Groups 1 and 2 and Groups 1 and 3. The next step was to look separately at all criteria. The results are presented as proportions of patients in whom image criteria were judged as fulfilled when all three observers were in agreement. Confidence intervals (CI) were calculated for proportions according to the binomial distribution. For the comparisons between Groups 1 and 2 and Groups 1 and 3 concerning residual gas and faeces, the 
2 test was used with the null hypothesis that there is no difference between the groups.
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Results
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232 patients were found to be eligible for this study between September 2003 and April 2004. 22 patients declined participation, and 210 were randomized to three groups with 70 in each group. Baseline characteristics are shown in Table 3. 34 patients dropped out after randomization. This resulted in 176 evaluated patients. The patient flow and main reasons for loss to follow up are shown in Figure 2.
The intention to treat analysis of image quality criteria using the t-test showed that the difference between Groups 1 and 3 is 0.00 (95% CI –0.19 to 0.19; p = 0.99) and between Groups 1 and 3 is –0.04 (95% CI –0.24 to 0.15; p = 0.66). In the power analysis, equivalence was defined as a difference between population means not larger than 0.5 points. The confidence intervals were in between those values.
The analysis of all criteria separately showed no statistically significant difference between groups (Table 4). A criterion was considered to be fulfilled only when all three observers were in agreement. Criterion number 2, i.e. kidney outlines before intravenous contrast administration, had the lowest score in all three groups, without any significant differences between the three groups. These results are supported by the ICS assessment, in which no significant difference was found between the evaluated groups (Table 5).
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Table 4. The result of assessment of examinations in all three preparation groups according to the European guidelines for image quality criteria
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Table 5. The result of assessment of examinations in all three preparations using the image criteria score(ICS) (a – before contrast administration; b – after iv contrast administration)
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The results of purgation assessment concerning the amount of gas and faeces are shown in Figures 3 and 4, respectively. Figure 3 shows that there is no difference between the groups concerning residual gas. Concerning residual faeces (Figure 4), the standard bowel preparation showed its effectiveness in the area of the right and left flexure. Significantly more patients in Group 1 than in the other two groups were assessed as equal to or better than those in the reference examination (right flexure: Group 1 vs Group 2, p<0.001; Group 1 vs Group 3, p<0.002). In the area of the left flexure, Group 1 vs Group 2, p = 0.01; Group 1 vs Group 3, p = 0.05. Figure 3 shows the equality of proportions in the areas of the right and left lower quadrant.
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Figure 3. Assessment of residual gas. Thex-axis shows the three preparation groups. The y-axis shows the proportion of examinations in which the amount of residual gas was assessed as equal to or better than that in the reference patient (grey bar) or worse than the reference (black bar).
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Figure 4. Assessment of residual faeces. Thex-axis shows the three preparation groups. The y-axis shows the proportion of examinations where the amount of residual faeces was assessed as equal to or better than that in the reference patient (grey bar) or worse than the reference (black bar).
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Discussion
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The results of our study show that fulfilment of the European Commission criteria was equivalent in the three preparation groups and confirm the findings of previous studies [1–5]. The high score in the assessment of visibility also means a high degree of interobserver agreement, as the criteria were considered to be fulfilled only when there was 100% agreement between all three readers.
As ICS is a mean of all criteria scores, it will be influenced by a lower score for visibility of the kidney outlines before administration of contrast medium (Criterion 2), and it gives a somewhat lower score compared with European Commission criteria assessment. However, there was still no significant difference between the three preparation groups.
The few exclusion criteria give the study good external validity.
There is a potential source of bias in our study in that we do not know how many patients did in fact follow our recommendation concerning preparation. We could have asked them, as was done in previous studies [1, 2], but a questionnaire is not a reliable way of evaluating bowel purgation and, in our opinion, it just moves confusion to a higher level. With adequate randomization, all three groups would be representative of an out-patient population and probably reflect its compliance.
Recommendations to patients regarding bowel preparation, fluid and dietary restrictions prior to excretory urography are an "old tradition" in radiology, but a review of the literature gave no answer about the origin of such recommendations. They were probably formulated early in the history of contrast radiography when the type and amount of contrast material, the radiographic equipment and techniques, and the lack of tomography limited the visualization of the urinary tract.
Theoretically, the ionic, high osmolar contrast media used in earlier studies [1, 4, 5] had an osmotic effect that resulted in increased diuresis and poorer contrast enhancement of the urinary tract. The visualization of the collecting system should be improved with the use of modern, low osmolar, non-ionic contrast media by virtue of lower diuresis. In fact, in agreement with the results of our study and irrespective of the type of contrast used, high osmolar [1, 4, 5] or low osmolar [3], none of the previous studies found a difference in the visibility of the urinary tract between groups of patients who were allowed to eat and drink and groups who fasted. Because of this and with concern for renal function, the policy of aggressive dehydration should and has been abandoned. Another advantage of the use of modern, low osmolar contrast media is their low frequency of complications such as nausea and allergic reactions, which renders the use of fasting for prevention of aspiration unnecessary.
As in the study conducted by Schuster at al [4], we used nephrotomography as a standard in this study. But, unlike the procedure in previous studies, we applied ureteral compression for adequate distension of the upper tract. The use of such compression is not mentioned in previous reports.
In contrast to the results of George at al [3], we found an equal amount of gas in the patients with standard bowel purgation and the other two preparation groups. The evaluation of the effects of purgation indicates that our standard preparation with bowel purgation and dietary restriction is effective in the flexure areas. Despite this, there was no difference in image quality between the standard preparation group and the other two groups, and the reproduction of the kidney outlines before contrast administration was poor in all three groups. This indicates that images obtained prior to the administration of contrast medium are not useful for evaluating kidney outlines. Administration of contrast medium and use of nephrotomography dramatically improved the visibility of the kidney outlines. The area of the right lower quadrant is probably hard to reach with purgatives, while the colon in the left lower quadrant is empty irrespective of the preparation method.
Recently introduced flat panel digital detectors offer improvements over conventional analogue imaging systems and allow more effective use of radiation and more efficient work practices without loss of image quality. The ability to view and adjust image settings directly at a workstation is one of its major advantages. The image viewing tools at a workstation such as window and level settings and zoom functions may give even better representation of low contrast objects such as the kidney and psoas outlines. Okamura et al [12] found that the image quality with a flat panel detector in abdominal imaging was superior to that with film–screen or storage phosphor plate systems even with a dose reduction of approximately 50%. Their results have been confirmed by Zähringer et al [13] except for the psoas margin stripe, where no significant difference was found between the two imaging techniques. In the latter study, the insignificant difference in depiction of the psoas margin was explained by the superposition of bowel gas, mucosal folds or faecal material.
In 1996, the European Commission established the image quality criteria for radiographic examinations to set the quality standard and minimize reader subjectivity. This was the main reason why we used the European guidelines score as a standard in the evaluation of image quality.
Previous studies [1–5] have shown no differences between preparation groups in terms of number of films required, duration of procedure, visibility of the renal tract and overall quality. Our study showed equality of three preparation methods using a standard investigation protocol with ureteral compression and tomography. To our knowledge, this is the only study planned and performed as an equivalence study with power to demonstrate the equality of the evaluated preparations.
This study adds to the growing evidence that bowel preparation before excretory urography is unnecessary and should be abandoned. We hope that our results can contribute to future uniformity of practice.
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Acknowledgments
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We thank Anders Magnuson, Örebro University Hospital, for his help with the statistical analyses.
Received for publication September 18, 2006.
Revision received November 8, 2006.
Accepted for publication November 22, 2006.
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References
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Abstract
Introduction
