Monday 10 November 2014

Do an ultrasound first for suspected kidney stones… if you’ve got the skills

You are seeing a patient in the ED with suspected renal colic. Should you do a point-of-care ultrasound first, a radiology ultrasound or just go straight to CT

Why not just CT everyone? After all, it is the gold standard test. Yes, but the authors correctly point out the radiation issues, cost and get kudos for mentioning morbidity from over-diagnosis and incidental findings. All of this coming from the lead author who is a San Francisco radiologist! (I wonder if she has had her keys to the radiology tea room revoked.)

Inclusion criteria were patients between 18-76 years old where the ER doctor decided to order imaging to establish or rule out a primary diagnosis of kidney stones.

Excluded patients included obesity, pregnancy, those at “high risk” for serious alternative diagnosis such as cholecystitis, appendicitis, AAA, bowel disorders and a few other things.

Patients were randomized in a 1 to 1 to 1 fashion to the first study being a point-of-care ultrasound, radiology ultrasound, or CT. After this was done, the ER doctor could do order whatever tests they felt appropriate.

There were three primary outcomes that all seem relevant but somewhat hard to measure.

The first was did the initial treatment strategy cause any harms? This was defined as high risk diagnosis with complications that could be related to a missed or delay in diagnosis. Three separate non-blinded reviewers determined this outcome and came to a consensus.

The other two outcomes were total radiation exposure and cost.

Results? 2759 patients were enrolled across 15 different ED’s. Most of these ED’s had a very active ultrasound program.40% of the patients had a prior diagnosis of kidney stones. Of the total, only 11 patients (0.4%) had a high risk diagnosis with complications in the first 30 days. There were no differences between the groups.

Of note, 60% of patients randomized to the point-of-care ultrasound never got a CT in the ED.

Not wanting to paraphrase an issue of such importance, the authors state the following:

“Our results do not suggest that patients should undergo only ultrasound imaging, but rather that ultrasonography should be used as the initial diagnostic imaging test…”

The obvious limitation to this study is external validity. I always seem to chuckle a little when I see a study of ultrasound that quotes test performance to three decimal points. The fact is that the sensitivity and specificity of the test will change each and every time a different person picks up the probe. This study clearly used doctors experienced in ultrasound. In addition remember they were also very good at excluding high risk patients on clinical grounds. Therefore caution is in order.

Will this change practice? As usual, the answer is it depends. It really matters who is holding the probe and making the clinical decisions. Nevertheless, this study gives strong support to those who might perform a point-of-care ultrasound without having to resort to CT if it was not felt to be indicated.

All of this from a radiologist…it must be a cold day in hell.


Smith-Bindman R, Aubin C, Bailitz J, et al. Ultrasound versus Computed Tomography for Suspected Nephrolithiasis. N Engl J Med 2014;371:1100-10.

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