Top 10 reasons NOT to order a CT scan for suspected renal colic

Top 10 reasons NOT to order a CT scan for suspected renal colic

CT_Scanner_01.jpg2d5efea2-a1b7-4c15-848e-4d6c5567eecfLargerExpertPeerReviewStamp2x200It appears that the excitement and utilization of computed tomography (CT) imaging in the emergency department (ED) has far outpaced our concern for the short- and long-term consequences of increased reliance on this technology. CT has greatly supplemented, or even replaced, our clinical decision making for many chief complaints.  Many articles document the dramatic increased CT use in contemporary practice, including a 330% increase in the rate of CT imaging from 1996 to 2007. The likelihood of a CT order being part of any ED encounter now approaches 15%, with no signs of decline.1

Rising trend for CT imaging for renal colic

This trend especially holds true in the evaluation of flank pain.2 Kocher cited CT utilization rates for cases of suspected renal colic between the years 1996 to 2007 have increased from 4.0% to 42%.1  This 10-fold increase in CT use occurred alongside a flat rate of urolithiasis diagnosis (18%) and hospital admissions for renal colic (11%) over the same period. During the same study period ultrasound (US) utilization was low to begin with, and only went down from 5% to 2.4%3. Yet, the American College of Radiology appropriateness criteria rates ultrasound as equivalent to CT for the abdomen to evaluate recurrent stones. For acute renal colic in general they highlight an option to use US over CT unless patients fail to respond to conservative management or in those in whom surgery is anticipated. Why the disconnect between the evidence, guidelines, and our current practice patterns in imaging for renal colic?

Why CT imaging indication creep?

Chen compared the results of 200 CT examinations over 2 years and demonstrated “indication creep;” that is, the percentage of cases with a ureteral stone decreased from 49% in the 1st year to 28% in the 2nd year, whereas the alternative diagnosis rate increased from 16% to 39%. The authors speculated that the indications for ordering unenhanced helical CT broadened because the ED physicians recognized over time that unenhanced helical CT is a rapid study that can be used to demonstrate not only ureteral stones but many alternative diagnoses.4

Yet, there is no study that I am aware of that has shown improved outcomes in renal colic associated with this aggressive imaging strategy.

Supporters of CT imaging

Proponents will cite studies that show significant alternative diagnoses rates found on CT for “suspected renal colic.” Goldstone’s study included 231 patients, with a serious alternative diagnosis rate of 6.5%, including5:

  • Pyelonephritis
  • Diverticulitis
  • Appendicitis
  • Pneumonia
  • Small bowel obstruction
  • Cholecystitis
  • Pelvic inflammatory disease

This was a retrospective chart review, and pre-test probability for renal colic versus an alternative diagnosis in the ordering providers’ minds cannot be ascertained. That is, how surprised were the clinicians when they received the radiology report of appendicitis? Was a complete history and exam done prior to all of these CT scan orders being placed? It is unclear in this study and others like it.6

Patient expectations?

Or maybe it has nothing to do with emergency physician diagnostic uncertainty and more to do with catering to the patient’s real or perceived expectations? Patients typically bring expectations to medical encounters, often making specific requests of physicians, and satisfaction correlates with the extent to which physicians fulfill patient expectations.7–9


Top 10 List

Below are my top 10 reasons to think about when considering a CT in your next suspected renal colic patient:

  1. Cancer risk: An isolated CT scan is incredibly safe, but 1-3% of cancer is estimated to arise from medical imaging. A typical radiation dose for a CT of the abdomen and pelvis is in the range of threshold increased cancer risk among atomic bomb survivors; for a 40-year-old male the increased risk is on the order of 1 in 1000.10
  2. Patient expectations: Symptomatic kidney stones are common, and they usually recur.  Recurrence rates are estimated at 50% over a 10-year and 75% over 20-year period, with some people experiencing ten or more episodes over the course of a lifetime.11,12 If you set the expectation that all ED renal colic visits get a CT (analogous to all upper respiratory illnesses getting a prescription for antibiotics), it can be difficult to overcome this inertia on subsequent visits from a client satisfaction standpoint.
  3. Imaging begets imaging: CT adds cost, time, and ionizing radiation exposure to the ED visit.  Malignant transformation risk from radiation is cumulative in patients who undergo multiple studies. 6,13
  4. Generally good prognosis: Spontaneous stone passage rates are high, estimated at over 90%. One can further prognosticate based on size and location of stone, but this is only useful if having a complicated course of renal colic, defined by prolonged or uncontrolled symptoms with or without persistent hydronephrosis or signs and symptoms of an obstructing urinary tract infection. 14  Clinically, complicated cases declare themselves.  In very high pre-test probability cases (good story and exam, positive hematuria) the CT is more likely to harm than help as incidental findings and cascade testing will outnumber serious alternative diagnoses.
  5. Hydronephrosis is not an emergency: Hydronephrosis on acute presentation in the ED does not mandate an intervention. The evidence supports that hydronephrosis does not lead to irreversible loss of renal function if corrected within a few weeks 15 . Ultrasound may not be as sensitive as CT for finding a patient’s kidney stone, but it is does very well at diagnosing hydronephrosis. 16
  6. Imaging begets urology referrals: Complications arise between 1-8% with urologic interventions (e.g. lithotripsy, ureteroscopy) and include sepsis, steinstrasse (stone street), stricture, ureteral injury, and UTI. 14 Unnecessary CT ordering in uncomplicated cases might compel an early urology referral, which might lead to an early unnecessary intervention. The patient who would have likely done well with conservative management now gets a new trajectory, one that carries increased morbidity and cost.
  7. Wait and see: This is not just for acute otitis media (AOM) anymore. Patients are 3 times less likely to fill an antibiotic prescription when given a time- and action-specific contingency plan for when to fill a prescription given for AOM in the ED. 17 Like AOM, renal colic is a largely self-limited clinical entity requiring supportive measures in the vast majority of cases.

Why not apply a similar approach to the CT order that many are doing now with antiobiotics for AOM?  If symptoms are controlled in the ED and the patient appears uncomplicated, they qualify for this algorithm. The timing of the “wait and see” decision might matter, although no researcher has examined this for renal colic. I have found that more patients will be accepting to defer a CT as their informed decision after their acute pain has been treated and resolved in the ED. There is evidence to show that patients with suspected renal colic who undergo delayed outpatient imaging have equivalent outcomes to those who undergo ED imaging at four-week follow-up. 18 A systematic review of shared decision making in the ED shows it has been able to decrease resource utilization while increasing patient satisfaction, erasing the misperception that one always needs to order the maximum workup on a patient to ensure high patient satisfaction scores. 19

  1. Reframing the question: Is finding the stone really the right clinical question to be asking? Instead, should we not be asking: what chance does my renal colic patient have of needing a urologic intervention, now or eventually? Because modern practice chases the former, we have largely left behind the ultrasound (US) in the diagnostic algorithm, since it often fails to visualize the culprit stone.  In a study of ED renal colic patients, 817 renal ultrasounds were examined for their predictive value of a urologic intervention. Of the 43% that resulted “normal” only 2 patients (0.6%) went on to a urologic intervention. That is, when the ultrasound is negative, you may still have a ureteral stone present somewhere, but it is highly likely to pass spontaneously. Of the 51% of patients with an US suggestive of or visualizing a stone, roughly 6.5% went on to a urologic procedure. 20 This further emphasizes the point that most renal colic cases are self-limited. It at least gives a framework to discuss options in real terms with the patient when deciding on an imaging strategy.
  2. UA + US = done: Emergency physicians have been shown to quickly learn how to accurately detect hydronephrosis at the bedside16,21 through an algorithmic approach. Hematuria on urinalysis (UA) is roughly 90% sensitive for a ureteral stone in acute flank pain. Ultrasonography (US) can increase the yield. In a study of 227, ED patients with acute flank pain, 122 were discharged without further investigation except urinalysis and bedside US. Ninety-nine had a urinary stone, and the others did not have a life threatening disorder. 22
  3. Low dose CT: If you still want a CT, consider ordering it low dose. Niemann showed that radiation exposure can be reduced by roughly 10- to 20-fold without a significant compromise to sensitivity (97%) and specificity (95%) when compared to standard effect dose ranges. 23  A variety of strategies and techniques exist to lower radiation exposure beyond simply not ordering the test. Protocols need to be developed between the ED and radiology departments for this to become a reality and not just a research novelty. 24

There will still be cases where the risk of benefit to harm is in favor of ordering a CT in suspected renal colic. Complicated renal colic occurs, but it usually declares itself clinically (uncontrollable pain and/or vomiting, signs and symptoms of an obstructing urinary tract infection). These cases will be the exception and not the rule.

Some rare alternative diagnoses (e.g. malignancy, renal infarct) can present nearly identical to renal colic, but these are not especially time sensitive and will be discovered via a “wait and see” approach generally.


To conclude, the vast majority of ED patients with acute renal colic do not need a CT. A urinalysis and bedside ultrasound will raise the pre-test probability adequately in most patients, if needed, and at least help screen for those who might go on to need an urologic intervention.  If a serious alternative diagnosis is really suspected or the patient fails to have their symptoms adequately controlled, a CT is reasonable. A low-dose CT is even more reasonable. Knowing they are receiving less radiation and possibly shortening their length of stay is likely to overcome any patient satisfaction lost by not ordering the CT.

Think before ordering that CT.

Kocher K, Meurer W, Fazel R, Scott P, Krumholz H, Nallamothu B. National trends in use of computed tomography in the emergency department. Ann Emerg Med. 2011;58(5):452-62.e3. [PubMed]
Smith R, Varanelli M. Diagnosis and management of acute ureterolithiasis: CT is truth. AJR Am J Roentgenol. 2000;175(1):3-6. [PubMed]
Westphalen A, Hsia R, Maselli J, Wang R, Gonzales R. Radiological imaging of patients with suspected urinary tract stones: national trends, diagnoses, and predictors. Acad Emerg Med. 2011;18(7):699-707. [PubMed]
Chen M, Zagoria R, Saunders H, Dyer R. Trends in the use of unenhanced helical CT for acute urinary colic. AJR Am J Roentgenol. 1999;173(6):1447-1450. [PubMed]
Goldstone A, Bushnell A. Does diagnosis change as a result of repeat renal colic computed tomography scan in patients with a history of kidney stones? Am J Emerg Med. 2010;28(3):291-295. [PubMed]
Broder J, Bowen J, Lohr J, Babcock A, Yoon J. Cumulative CT exposures in emergency department patients evaluated for suspected renal colic. J Emerg Med. 2007;33(2):161-168. [PubMed]
Marple R, Kroenke K, Lucey C, Wilder J, Lucas C. Concerns and expectations in patients presenting with physical complaints. Frequency, physician perceptions and actions, and 2-week outcome. Arch Intern Med. 1997;157(13):1482-1488. [PubMed]
Kravitz R, Bell R, Azari R, Krupat E, Kelly-Reif S, Thom D. Request fulfillment in office practice: antecedents and relationship to outcomes. Med Care. 2002;40(1):38-51. [PubMed]
Macfarlane J, Holmes W, Macfarlane R, Britten N. Influence of patients’ expectations on antibiotic management of acute lower respiratory tract illness in general practice: questionnaire study. BMJ. 1997;315(7117):1211-1214. [PubMed]
Berrington de, Darby S. Risk of cancer from diagnostic X-rays: estimates for the UK and 14 other countries. Lancet. 2004;363(9406):345-351. [PubMed]
Weiss M, Liapis H, Tomaszewski J, Arend L. Pyelonephritis and other infections, reflux nephropathy, hydronephrosis, and nephrolithiasis. In: Jennette J, Olson J, Schwartz MM, Silva FG, eds. Heptinstall’s Pathology of the Kidney. 6th ed. Lippincott Williams & Wilkins; 2007:991-1082.
Moe O. Kidney stones: pathophysiology and medical management. Lancet. 2006;367(9507):333-344. [PubMed]
Brenner D, Hall E. Computed tomography–an increasing source of radiation exposure. N Engl J Med. 2007;357(22):2277-2284. [PubMed]
American Urology Association Practice Guidelines 2007 for Management of Ureteral Calculi. Am J Roentgen. 2002;178: 101-103.
Pain V. Pathophysiology of urinary tract obstruction. In: Campbell-Walsh Urology. Vol 2. 9th ed. Saunders; 2007:1227-1273.
Riddell J, Case A, Wopat R, et al. Sensitivity of emergency bedside ultrasound to detect hydronephrosis in patients with computed tomography-proven stones. West J Emerg Med. 2014;15(1):96-100. [PubMed]
Spiro D, Tay K, Arnold D, Dziura J, Baker M, Shapiro E. Wait-and-see prescription for the treatment of acute otitis media: a randomized controlled trial. JAMA. 2006;296(10):1235-1241. [PubMed]
Lindqvist K, Hellström M, Holmberg G, Peeker R, Grenabo L. Immediate versus deferred radiological investigation after acute renal colic: a prospective randomized study. Scand J Urol Nephrol. 2006;40(2):119-124. [PubMed]
Flynn D, Knoedler M, Hess E, et al. Engaging patients in health care decisions in the emergency department through shared decision-making: a systematic review. Acad Emerg Med. 2012;19(8):959-967. [PubMed]
Edmonds M, Yan J, Sedran R, McLeod S, Theakston K. The utility of renal ultrasonography in the diagnosis of renal colic in emergency department patients. CJEM. 2010;12(3):201-206. [PubMed]
Mandavia D, Aragona J, Chan L, Chan D, Henderson S. Ultrasound training for emergency physicians–a prospective study. Acad Emerg Med. 2000;7(9):1008-1014. [PubMed]
Kartal M, Eray O, Erdogru T, Yilmaz S. Prospective validation of a current algorithm including bedside US performed by emergency physicians for patients with acute flank pain suspected for renal colic. Emerg Med J. 2006;23(5):341-344. [PubMed]
Niemann T, Kollmann T, Bongartz G. Diagnostic performance of low-dose CT for the detection of urolithiasis: a meta-analysis. AJR Am J Roentgenol. 2008;191(2):396-401. [PubMed]
Sung M, Singh S, Kalra M. Current status of low dose multi-detector CT in the urinary tract. World J Radiol. 2011;3(11):256-265. [PubMed]

Expert Peer Review

Before you read any further, be warned that I am of the opinion that we need to find alternatives to CT scan for the evaluation of patients presenting with suspected kidney stones and am in agreement with the top 10 reasons not to get a CT scan, and will not be discussing the contrarian view. Instead, I would like to make a few observations about how we arrived at this degree of CT utilization, as well as the direction we emergency physicians should take in order to safely decrease our use of CT going forward.

A close reading of the seminal articles by Smith that proved the superiority of CT scan over IVP reveals that CT scan was intended to be used in patients who would otherwise be referred for IVP. In a subsequent publication, Smith concluded that:

“Unenhanced CT is a valuable technique for examining patients with acute flank pain in whom a clinical diagnosis is uncertain” [1].

That seems to be a far cry from how CT scan has been used in the past decade, and the blog as well as many authors have described the phenomenon of indication creep. Aside from actual evidence based reasons for the increased use of CT scan, as well as patient expectations, other drivers of CT use likely include increased availability of CT scan, improved technology, economic incentives, and physician attitudes towards risk tolerance, uncertainty, and fear of malpractice.

Perhaps another reason for the rapid adoption of CT scan for the evaluation of patients with suspected kidney stone is explained by our metric for diagnostic tests – we commonly assign value to measures of sensitivity, specificity, predictive values, and likelihood ratios, rather than patient oriented clinical outcomes. As Daniel points out, there is little evidence to show improved patient outcomes for CT scan in patients with suspected kidney stone. In fact, our NHAMCS survey by Westphalen et al shows the opposite – despite a 10-fold increase in CT scan use between the years of 1996-2007, there was no change in the rate of kidney stone diagnosis, alternate diagnoses, or hospital admission.

The evidence-based assessment of diagnostic tests should include patient oriented clinical outcomes. I am aware of potential solutions to the overuse of CT scan for suspected kidney stones on the horizon. One is the development of clinical prediction rules for kidney stone – Chris Moore recently reported the derivation and initial validation of a clinical prediction rule for the presence of kidney stone on CT scan [3]. While this rule will require external validation and impact analysis prior to broad adoption, it is a promising step in the development of a tool to help emergency physicians identify which patients require imaging and those who do not.

A second solution is ultrasound – both point of care ultrasound and radiology ultrasound. Stay tuned for the results of a multicenter randomized clinical trial comparing CT scan to ultrasound for patients with suspected kidney stone. It is possible that an algorithm combining a clinical rule and ultrasound could limit CT scan use to those who truly need it.\"


  1. Smith RC, Verga M, McCarthy S, Rosenfield AT. Diagnosis of acute flank pain: value of unenhanced helical CT. AJR Am J Roentgenol. 1996 Jan;166(1):97-101.
  2. Westphalen A, Hsia R, Maselli J, Wang R, Gonzalez R. Radiological imaging of patients with suspected urinary tract stones: national trends, diagnoses and predictors. Acad Emerg Med. 2011; 18: 700-707.
  3. Moore CL, Bomann S, Daniels B, Luty S, Molinaro A, Singh D, Gross CP. Derivation and validation of a clinical prediction rule for uncomplicated ureteral stone--the STONE score: retrospective and prospective observational cohort studies. BMJ. 2014 Mar 26;348:g2191. [free PDF of full article]
Ralph Wang, MD
UCSF Associate Professor of Emergency Medicine

Expert Peer Review

Really great to see more conversation on this, and that EM is becoming actively involved in the discussion as well as the research. Read more about EM\'s involvement in the Choosing Wisely campaign and development of our own lists for emergency medicine [JAMA Internal Medicine 2014 citation].

Renee Hsia, MD MPH
UCSF Associate Professor of Emergency Medicine

Daniel Firestone, MD RDMS

Daniel Firestone, MD RDMS

Emergency physician
Kaiser Permanente Hospital, Orange County
  • John Litell

    Thanks for this great post, and for challenging dogma (or in this case, reminding us how we used to do things, surprisingly recently). The elephant in the room in any discussion about sudden severe flank pain–and, right or wrong, part of the rationale for CT–is dissecting AAA (illustrative cases at PMID 22691630, 23900449, & 16874695).

    I’m all for pursuing a UA/US-guided approach, perhaps as an ED observation protocol. It would help if this post at least mentioned the elephant and some associated data. Did you come across anything useful?

  • Dan Firestone

    John: thanks for the comment! AAA is indeed an elephant, but I would argue it shouldn’t be in the room of many of our renal colic patients. Patients need to be “in the range” to think this is realistic.

    1) AAA almost never exists under 50 years of age.
    Forsdahl SH, Singh K, Solberg S, Jacobsen BK. Risk factors for abdominal aortic aneurysms: a 7-year prospective study: the Tromsø Study, 1994-2001. Circulation 2009; 119:2202.

    2) AAA >4cm almost never exists under 55 years of age.
    Singh K, Bønaa KH, Jacobsen BK, et al. Prevalence of and risk factors for abdominal aortic aneurysms in a population-based study : The Tromsø Study. Am J Epidemiol 2001; 154:236.

    3) risk of AAA rupture takes off dramatically at 5.5cm diameter, something you can screen for very quickly with a bedside ultrasound (right before you look for hydronephrosis).
    Powell, JT, Greenhalgh, RM, N Engl J Med 2003;

    If bedside US is unavailable or you’re not trained you can add on to your radiology order of the renal US. I don’t really start looking until older than 50-55 years.

    4) Many patients have had a CT done in the past few years and you can reference this in your medical decision making to justify why you’re not rescanning. AAA 5.5cm grow faster at 3-4mm/year.
    Brady AR, Thompson SG, Fowkes FG, et al. Abdominal aortic aneurysm expansion: risk factors and time intervals for surveillance. Circulation 2004; 110:16.

    For example, if I clinically suspect someone has renal colic and I do a bedside US and the aorta is 3.8cm, I feel confident stating the pain is not from the AAA and I set the patient up for outpatient followup.

    If I do a bedside US and the aorta measures >5cm, and even more worrisome if >5.5cm, I then order a CT angiogram and the patient doesn’t go home without talking to and/or being seen by vascular surgery. They may end up having a non-aortic cause of pain, but a “symptomatic AAA” looks just like an “asymptomatic AAA” on CT if there’s not bleeding, yet. There is a phenomenon of pain from the aorta prior to actual rupture in many cases.

    5) Realize that CT KUB is great for picking up AAA and will tell you if it’s leaking, although not pinpoint the anatomy well.

    But it doesn’t pick up aortic dissection, a totally different entity, much less predictable since it can occur in the young with connective tissue problems, vasculitis, etc. Dissection usually starts thoracic and if goes to the abdomen you may very well miss it with a routine CT KUB protocol for kidney stones, since the caliber of the abdominal aorta in these patients may well be normal. You need IV contrast, ideally arterial phase, to pick up the dissection flap.

    6) Bottom line, you’ll miss dissection frequently if all you order is CT KUB. It’s a different kind of elephant all together.

    Also note that for AAA high suspicion, you want CT angio to map the anatomy, as the vascular surgeons need this to decide repair options (endovascular vs open), you’ll need to tell the CT tech to extend down to the proximal thighs as well, since they want to look for dense plaque in the femorals to see if they can fit the stent through those vessels. If you do it wrong you’ll have given an IV contrast load and the surgeon won’t have all the info they need…can cause delays (I speak from having done this :).

    Hope that’s useful, John. Take care!

    • John Litell

      That’s perfect Dan. Just what I had in mind – just thought it deserved to be in the post. Thanks for the quick & thorough update!

  • Anand Senthi

    great discussion. Surprised to read the implication from the above post, that low dose (non-contrast) CT is NOT the standard of care CT scanning protocol in the US for renal colic. In Australia, at least in my state, it is the only acceptable CT scanning protocol for renal colic. Consequently we’ve developed a very reasonable protocol where patients presenting with their first ever episode of renal colic in their lifetime get a low dose CT, while recurrent presentations in a patient with a history of renal colic get an U/S. Definitely agree that CT should not beget further CTs.

    • Dan Firestone

      Anand, you should be surprised…as it makes no sense that we’re so behind with this. The technology is there, just need the will as a profession in the USA, particularly on a local level, as that seems to be how these practice decisions get made. Individual radiology/ED practices differ so much in how they image. For instance, in general abdominal CT’s, some institutions require oral and IV contrast for common conditions such as appy/tics/etc, whereas others don’t require any at all, or some may want IV only. But only after all the involved stake-holders have sat at meetings and hashed it out and shaken hands on the topic do any of these change, usually long after the evidence says it’s ok to do so.
      thanks again, Dan

      • Anand Senthi

        I hear you and it must be frustrating! We also have local variation in CT practice but thankfully not so much on (renal colic protocol) low dose CT.

  • Pik Mukherji

    Nice discussion, I’m nearly in agreement, except:

    U/A is “90% sensitive”? Yes and with poor LR (1.4ish?)
    U/S is preferred modality? Adds little to management, same as your expert review comments on CT.

    Bottom line:
    Imaging is for diagnostic certainty, not management.
    U/A is ” rule out infected stone, ” not “rule in stone.”
    You don’t need an U/S either.

    • Dan Firestone

      Great points Pik, I agree with you. If pre-test probability is high for stone and (more importantly) very low for important alternatives, you don’t need any imaging. It does help you decide if someone has MSK vs renal colic as a source of their pain, and risk stratify their need for urologic intervention. It also can screen for AAA quickly. If you left it out, which I do frequently (e.g. too young for AAA, or had a prior imaging study to refer to), you don’t lose much. For those uncomfortable with a clinical only approach to renal colic, the ua plus US approach satisfies the diagnostic certainty issue noninvasively.
      UA doesn’t even rule in infected stone really well. The infected ones look sick, and many + UA’s aren’t true positives. They may be colonized or have pyuria from the whole blood in the urine or irritation, but there’s no evidence to suggest that treating pyuria with stone without clear infectious symptoms helps anybody. We just get concerned in case they bounce back infected and we “ignored the +UA”, even more so than we do with pyuria without stone (which also gets overtreated).

      • Pik Mukherji

        Great points, 1st sentence of which is most important: Making AAA and torsion unlikely >> ruling in stone. And differentiating MSK from stone? Don’t care.