The Trial

Smith-Bindman R, Aubin C, Bailitz J, Bengiamin RN, Camargo CA Jr., Corbo J, et al. Ultrasonography versus Computed Tomography for Suspected Nephrolithiasis. N Engl J Med. 2014 Sep 18;371(12):1100–10. 

They managed to come up with the STONE trial as acronym for this one. [Study of Tomography Of Nephrolithiasis Evaluation]

This is big news for USS, as it’s an RCT of the use of ED US use. Ultrasound, of course, makes sense to lots of us who see the probe as some sort of prehensile extension of the human body able to go forth and grasp the diagnosis. Still it’s nice to have some data to help us better understand how it helps our practice.

Here’s the details as I read them.

METHODS

• multi centre randomised trial. All good so far
• Randomisation could have been better described I thought
• 3 Groups
  • ED performed US by an EP credentialed in US – unclear if these were US super users or just regular punters with basic level US skills
  • Radiology perfromed US
  • CT
• The first major concern is in the lack of blinding. Though it’s hard to see how you could blind this.
• the ultimate decisions on imaging and disposal after the randomised imaging were down to the EP looking after the pt. So people afer US could go on to have CT if this was felt to be needed
• Unclear if the EP looking after the doc was also looking after the patient
• 3 Primary outcomes (which is a tad naughty. The prmary outcome should of course be, primary I would have thought)
  • “high-risk diagnoses with complications that could be re- lated to missed or delayed diagnoses”. The obvious one here might be a missed AAA for example. the missed pathology was pre defined and categorised by a number of the authors all independent of each other.
  • cumulative radiation exposure (does imaging beget imaging)
  • total costs (which I presume is for a different paper, as it’s not reported here)
• follow up was by repeated phone calls and a structured interview
• diagnostic accuracy was a secondary outcome but the gold standard here was the patient reporting stone passage or surgical removal. This is important as most people consider CT as the gold standard but as this is one of the modalities being assessed it would be “incorporation bias”  to include CT in the gold standard

RESULTS

• screened 3700, took 2700
• 3-5% lost to follow up which may be a problem – is the reason they didn’t answer the phone at follow up due to the fact they were dead? The reassuring thing is that lost to follow up was similar between groups
• 40% in this trial had a prior history of stone
• most were youngish and the most of the time the doc had a >50% pre-test probability of stone. Which is common – stones are usually obvious and most CTs we do for stone are positive, at least in my experience anyhow
• only 8% were admitted from the ED. This is amazing to me as we admit almost all our query stones. Either because we can’t get a CT at 3am for a stone (let’s face it the priority is pain control not diagnosis here) or because we need to get them a urologist (who only have a weekday service in our place). Our admissions are short but still, it’s nice to see that it is more than possible to manage these as out patients in a less dysfunctional system than ours in Ireland.
• Primary outcomes
  • the missed high risk diagnoses were tiny (you have to look in the supplementary appendix for this
    • ED US – 6. One bowel obstruction but mainly people returning with infections
    • Rad US – 3  – one missed ovarian torsion and the others infective
    • CT – 2 – infective complicatons
    • All of these were less than 1% and of course when the numbers are this tiny, there’s no statistical difference between them. Worth noting that the infective complications are going to be there no matter what you do, no imaging is going to be definitive for pyelo most of the time.
• There was significantly less radiation in both US groups. Which is hardly surprising. The excess radiaiton in the CT group was all due to the index CT and not lots of follow up CTs thankfully.
• One of the most interesting things to me was the accuracy of all 3 tests. Remember that the gold standard here was stone passage of surgery. All 3 tests had identical sens/spec. Sensitivity of 85% and spec of 50%.
• 40% of those in the ED US group went on to have a CT anyhow at the docs discretion. 27% of the rad group went on to have CT. Again, this is hardly surprising. People simply don’t trust US and most urologists want a CT, I know ours do. Despite the fact that even their guidelines suggest US as the investigation of choice if available.

THOUGHTS

• This is a great effort and a substantial trial. As we probably already knew, EP performed US appears safe and accurate when we pose a focused question. There will always be misses but the numbers here are tiny and are more clinical judgement related than imaging related.
• The issue will be dealing with the specialists who may not be able, or willing to deal with just the US. I don’t say that to be critical, there may be lots of good reasons to pursue further imaging, but there doesn’t seem to be much need for the young, uncomplicated, clinically typical stone.

Finally, the entire study protocol is available as a PDF of supplementary material on the NEJM site and is a fascinating insight into the background of putting together an RCT and the sheer volume of work required for it.

Want more renal ultrasound:

• Ultrasound podcast
  • Renal Ultrasound
  • 1 Min Ultrasound Video
• Sinai EM US
• EM:RAP Mini on the study with the author