Non-contrast computed tomography (NCCT) is the gold standard investigation for suspected renal calculi as it offers kidney stone identification in > 99% of cases. The British Association of Urological Surgeons (BAUS) guidelines1 recommend that NCCT should be performed within 24 hours of first presentation of suspected renal colic. However, critics maintain that NCCT is overused as the condition is not life-threatening and the majority of kidney stones less than 5 mm pass spontaneously.2
The preferred imaging for this clinical presentation has changed over the past two decades, with intravenous urography (IVU) being the investigation of choice in the 1990s. However, as computed tomography (CT) imaging improved and became able to detect renal calculi at an increased rate, IVU was phased out. A study by Eikefjord et al.3 found that CT was not only more cost-effective than IVU, but also more effective at detecting renal calculi.3
Non-contrast computed tomography is also expensive compared with imaging modalities such as abdominal radiography and abdominal ultrasound and an additional drawback is the potentially harmful effects of the radiation dose involved. Even if a kidney stone has been found, it is by no means likely that urological intervention will be needed.4 It has been suggested that, in order to minimize the exposure to radiation, a viable alternative needs to be found. If a positive CT rarely changes management, or results in any form of intervention, is it strictly necessary? Indeed, studies have shown that ultrasound combined with radiography is able to identify clinically significant kidney stones and is an effective predictor of the need for intervention.5,6 Studies suggest that, even in patients with known nephrolithiasis, repeat CT changes the management of only a small number of cases.7
This audit aimed to discover how many of the patients admitted to the surgical triage unit (STU) at North Manchester General Hospital had scans in keeping with the current guidelines, but to also discover how a positive scan changed overall management.
Our audit group looked at 144 patients admitted to the STU at North Manchester General Hospital with suspected renal colic between November 2010 and January 2012 (Figure 1). The picture archiving and communications system (PACS) and automated letter systems were used to find out how many of these patients did in fact have renal colic, what radiological investigations were performed, how many patients with suspected renal colic underwent NCCT within 24 hours, 48 hours and 6 months and how many underwent further intervention.
Of the 96 patients who presented for the first time with renal colic, only 19 patients (19.8%) underwent NCCT within 24 hours (Table 1 and Figure 2). Fifty-nine patients (61.5%) underwent NCCT within 6 months of presenting with renal colic and three patients required surgical/radiological intervention (two underwent NCCT within 24 hours of presenting with renal colic and one did so 1 month after presentation). The most popular investigations were abdominal radiography, carried out in 86.5% of patients, and abdominal ultrasound, performed in 31 patients (32.3%).
From this audit, it appears that, despite the BAUS guidelines, very few patients presenting with suspected renal colic are receiving the advised imaging within 24 hours as recommended. In fact, only slightly over half had the scan within 6 months of initial presentation. However, through this audit we demonstrate that, for this group of patients, there is a relatively low rate of urological or radiological intervention following scanning. In this study, only two patients who had underwent the recommended CT imaging within 24 hours actually went on to receive any sort of intervention. Of those patients who did not undergo CT imaging within 24 hours, one required subsequent intervention. These results beg the question of whether this imaging is required.
Studies have shown that a combination of radiography and ultrasound is effective in identifying patients at high risk of requiring intervention.5,6 It is important to consider the real need for CT scans if there is a viable alternative that can reduce exposure and be performed at a lower expense. In this audit, 86.5% of patients underwent abdominal radiography but ultrasound of the abdomen was performed in only 32.3% (Table 1 and Figure 2). It appears that most patients who present with abdominal pain with renal colic as one of the differential diagnoses undergo abdominal radiography. It can be argued that if patients automatically receive this imaging, bearing in mind the studies mentioned above, it would be more cost-effective to subsequently order an ultrasound of the abdomen. From these data, it appears that relatively few patients undergo ultrasound at any point and it can be argued that this is therefore an underused diagnostic tool as, when used in combination with radiography, ultrasound can effectively predict who is at low risk of requiring intervention.
Henderson8 argues that the use of diagnostic radiation has become excessive and draws attention to the work of Katz et al.,9 who found that 4% of the patient population studied underwent unenhanced CT on three or more occasions and were exposed to between 20 and 154 mSv of radiation.
However, it cannot be denied that CT is a highly effective method of diagnosing renal calculi. Studies comparing CT scanning with other imaging methods have found it to be superior. A study conducted by Mitterberger et al.10 found that CT identified the calculus in 100% of patients with confirmed renal calculi, with 100% specificity and sensitivity. These patients also underwent radiography and ultrasound, and this combination was 96% sensitive and 91% specific. This shows that, although there are alternatives that have high success rates, CT is still superior in its ability to detect smaller kidney stones.10
Computed tomography also has a use in identifying alternative diagnoses in patients who do not have renal calculi. Owing to the nature of the scan, it provides information about more than just the renal tract. One study found that, of 1035 patients who underwent CT for suspected renal colic, 14% had non-kidney stone-related pathology necessitating treatment and 68% had calculi coupled with a second pathology.11
A study conducted in 2007 comparing the diagnostic ability of standard-dose and low-dose CT in patients with a body mass index (BMI) of under 30 kg/m2 and kidney stones over 3 mm found that the sensitivity and specificity of low-dose CT were very similar to those of standard-dose CT.12 A second study found similar results, reporting that there was no significant difference in the results from low-dose and standard-dose scanning for kidney stones over 2 mm in size.13
One possible compromise seems to be the use of radiography and ultrasound to risk stratify patients to determine which are at high risk of requiring intervention and then consider the need for CT. This will undoubtedly increase the length of time between presentation and the CT; however, it does seem pertinent to have a concrete risk stratification system before ordering potentially harmful scans.
A useful addition to this audit would be to include a section reporting on the final diagnosis of these patients and also the findings from CT. This audit included data from all patients who presented to the STU and in whom renal colic was legitimately considered in the differential diagnoses at first presentation. The final diagnosis (or lack thereof) was not included in the audit pro forma. Thus, CT of the kidneys, ureters and bladder (KUB) may not have been considered necessary once further investigation was undertaken. It may also be useful to include further details of the patient’s presenting complaint, and it would be valuable to know which presenting symptoms were more likely to result in CT. Some studies3,4,9 have found that women presenting with flank pain are a particularly difficult diagnostic group. One study which looked at the positive rate in patients who underwent CT for suspected renal colic found that the positive rate was much lower in women, who were therefore needlessly exposed to radiation.3 It would be valuable to differentiate between the sexes in this audit in order to see how sex affects prognosis and therefore the value of CT.
This study showed that, within the Pennine Acute Trust, a mere 19.8% received the recommended imaging within the recommended time period. However, with studies5,6 showing the efficacy of a combination of abdominal radiography and ultrasound, the question remains whether CT imaging is necessary considering the efficacy of other investigations and the small numbers requiring intervention. Is it purely academic to subject the patient to CT when there are effective, cheaper and less harmful alternatives?