The Value-Add of Ultrasound to STONE Score

There are a few major questions to be addressed in patients with suspected renal colic:

• Is there an infection?
• If there is a stone, will it pass spontaneously or require urologic intervention?
• If I make a clinical diagnosis without CT, will I miss an important alternative diagnosis mimicking stone?

The STONE score addresses the last question – using a weighted decision instrument to classify patients with suspected stone into low-, moderate-, and high-risk cohorts for ureteral stone disease.  There are some issues with face validity for STONE, and likewise the validation has shown its performance to be somewhat inexact.  However, it helps reinforce gestalt and aids in shared decision-making.

This study adds in point-of-care ultrasound to assess the degree of hydronephrosis.  The hope of these authors was the presence of hydronephrosis would improve the performance of the STONE score by identifying the few patients with stones at the low- and moderate- end, while also using moderate or greater hydronephrosis to predict the need for subsequent urologic intervention.

The answer: only marginally.

Generally, the most useful positive likelihood ratios are above 10, and the most useful negative likelihood ratios are below 0.1.  In this study, only one LR potentially met that criteria.  The presence of moderate or greater hydronephrosis in a patient with a low likelihood of stone disease had a +LR of ~20 for both the presence of stone and for stone disease requiring urologic intervention – but this +LR was based on only a handful of patients, and the 95% CIs range from 4 to 110.

Lastly, did the presence of hydronephrosis rule out any important alternative diagnoses?  No.  Out of 835 patients, there were 54 with an important alternative diagnosis.  There were 11 patients with hydronephrosis plus an important alternative, including 3 appendicitis, 1 cholecystitis, 2 diverticulitis.  The presence of moderate or severe hydronephrosis was helpful, but would not obviate imaging for an alternative diagnosis if indicated.

“STONE PLUS: Evaluation of Emergency Department Patients With Suspected Renal Colic, Using a Clinical Prediction Tool Combined With Point-of-Care Limited Ultrasonography”
http://www.ncbi.nlm.nih.gov/pubmed/26747219