We used the NHMACS survey to examine trends in radiological testing rates in patients presenting to EDs with flank or kidney pain. Over the study period, there was a marked rise in the utilization of CT scans; specifically, we found a greater than 10-fold increase from 1996–1998 through 2005–2007. During the same period of time, the proportion of patients who did not receive imaging and the proportion receiving US each decreased by half.
We can only hypothesize why US utilization has decreased over time, but this is likely a multifactorial process, including 1) the superior accuracy of CT scan, 2) resource availability, and 3) increased clinician intolerance for diagnostic uncertainty. CT scan has been shown to have near perfect accuracy, detecting even minuscule stones. Although the results of our study suggest otherwise, prior studies have found CT better than US for the diagnosis of alternate causes of symptoms. In many institutions, US are only available during certain hours. CT image acquisition is faster, and scanners are often continuously available in the ED. Finally, it has been shown that high-risk specialist physicians, such as emergency physicians, have identified ordering diagnostic imaging as a common act of defensive medicine.33,34
Other factors (e.g., patient expectations, increasing radiologist preference for CT rather than US) may have also played a role in the decrease utilization of US in the United States.
Despite the superiority in accuracy of CT scan (vs. US) for urinary tract stones as well as significant thoracic and abdominal alternate diagnoses, we found essentially no change in the proportion of patients diagnosed with kidney stone, proportion of patients admitted to the hospital following imaging, or proportion of patients diagnosed with an alternative acute infectious or inflammatory diagnosis. These findings suggest that the increased utilization of CT scan in patients with suspected urolithiasis may not have had a significant effect on diagnosis or management of urolithiasis.
Because of the evidence suggesting that CT scans have not had a major clinical effect on the evaluation or management of adults with suspected urolithiasis, we explored whether non-clinical factors might be contributing or accounting for increased CT utilization rates. We found that there were a number of predictors for CT utilization in 2005 through 2007, including patient (male sex, severe acuity of pain, time in triage, other race/ethnicity) and hospital (northeast hospitals, urban hospitals, non-physician providers) characteristics. Some of these findings are expected; for example, acuity of pain and time in triage are patient factors that signal the need for and an increased urgency to correctly assess patients who are more ill-appearing. It is unclear why men were more likely than women to get a CT scan, but it is not uncommon to prefer an US in lieu of a CT scan for female patients, in particular, those of reproductive age. While for men the gonads can be easily shielded during acquisition of a CT scan, for women the ovaries are often directly exposed to the field of the radiation. Our results, however, showed that this difference persisted after controlling for age. Patients of other race/ethnicity were less likely to have a CT scan, but because this is a very heterogeneous group, it is difficult to find an explanation that is suitable for all patients within this category.
We attempted to explain differences in imaging acquisition based on hospital characteristics and geography given previous literature suggesting such variations. It is possible that urban EDs serve as referral centers and therefore provide service to more patients with more severe clinical findings, triggering a higher number of CT scans. Kirsch et al., in a study that investigated imaging utilization in EDs of 41 states, found that patients visiting higher-volume EDs were more likely to have CT scans.35
Another potential explanation is that urban centers have a greater number of EDs with CT scanners, and a greater number of scanners per ED, compared to rural institutions.36,37
Even after controlling for these factors, however, significant geographic variation in use of noninvasive diagnostic imaging, as shown in other studies, still persists.38,39
In the seminal study published in 1995, Smith et al. showed the superiority of CT scan for the identification of ureteric stones (comparing it to intravenous urography).40
Since this time, CT scan has essentially replaced intravenous urography in patients with suspected kidney stone. In several subsequent studies, CT scan has also been shown to be more accurate than US in the detection of kidney stone, especially with small ones.17,18,41
However, there is a dearth of evidence supporting the use of CT scan over US in terms of clinical efficacy or patient safety. This is in the context of growing evidence that CT scan utilization results in exposure to ionizing radiation (a known carcinogen),42–45
increased detection of incidental findings,46
and increased health care costs.
Our results are aligned with those reported by Pines.27
In this recent study, it was shown that the utilization of imaging modalities to assess patients with abdominal pain in EDs has increased over time, in particular the use of CT. That study, however, excluded patients with urinary tract stones. One single-institution Canadian investigation that studied patients with suspected urolithiasis also suggested an increase in use of CT, which was not accompanied by a significant change in the rates of true renal stone disease or alternate diagnoses.47
This study, however, did not address trends in utilization of alternative modalities such as US.
Our findings contribute to the literature by showing that the conventional argument for the choice of CT over US in the evaluation of flank or kidney pain in the ED is not supported by any evidence that increased use of CT scans have changed diagnosis or treatment rates. Some health care providers may assert that CT utilization is less critical for ruling-in nephrolithiasis and more critical for ruling-out dangerous alternative diagnoses. However, our results also do not support this contention; the percentage of alternative acute infectious or inflammatory diagnoses have not increased in parallel with CT utilization. Similarly, acute cardiovascular events and malignant neoplasms were uncommonly seen in our study population. These findings suggest that, at least if measured by alternative diagnoses or hospital admissions, CT imaging has not improved either of those goals.