April’s journal club looked at four clinical questions regarding the diagnosis and expectant course of renal stones. Can the STONE score help you determine if your patient’s flank pain is due to a renal stone? Which is better to confirm your clinical suspicion of a renal stone, ultrasound or CT? How likely will your patient’s kidney stone pass spontaneously? What is the accuracy of hematuria to predict a renal stone in the patient with flank pain?

Articles reviewed

Moore et al. Derivation and validation of a clinical prediction rule for uncomplicated ureteral stone - the STONE score: retrospective and prospective observational cohort studies. BMJ 2014; 348:g2191 doi: 10.1136 March 26 2014. [Pdf]
Coll et al. Relationship of Spontaneous Passage of Ureteral Calculi to Stone Size and Location as Revealed by Unenhanced Helical CT. ARJ: 178, January 2002. [Pubmed]
Smith-Bindman et al. Ultrasonography versus Computed Tomography for Suspected Nephrolithiasis. The New England Journal of Medicine. 371; 12, September 18, 2014. [Pubmed]

additional reading

Luchs; et al. Utility of Hematuria Testing in Patients with Suspected Renal Colic: Correlation with Unenhanced Helical CT Results. Urology 59 (6), 2002. [Pubmed]

MOORE ET AL.

This was a combination retrospective then prospective observational study of about 1600 adult patients. The STONE score was found to reliably predict the presence of uncomplicated ureteral stones and lower likelihood of acutely significant alternative findings. Exclusion criteria were history of trauma, evidence of infection, active malignancy, known renal disease, and previous urologic procedure (lithotripsy, stenting). The STONE score does what it is supposed to do: 10% in low score group (0-5) had stones, 50% in moderate score group (6-10), and 90% in high score group (10-13). In all groups, acutely significant alternative causes of symptoms were found in about 3% of patients. In the high score group, only 0.3-1.6% had acutely significant alternative findings.

Bottomline: The STONE score is a clinical prediction rule that can help identify patients with a high probability of uncomplicated ureteral stone and absence of other important causes of symptoms (eg. diverticulitis, AAA, malignancy). In patients who fall in the high score group (especially young patients more at risk for negative effects of CT’s) consider using ultrasound instead of CT.

COLL ET AL.

This was a retrospective study of 172 adult patients with confirmed stones. As expected, when looking at size alone, smaller stones were more likely to pass spontaneously than larger stones: 78% of 1-4 mm stones; 60% of 5-7 mm stones; 39% of >/= 8 mm stones. When looking at location alone, distal stones were more likely to pass spontaneously than proximal stones: 48% for proximal; 60% for mid-ureter. Stones found at the uretrovesicular junction (UVJ) had a 75% chance to pass spontaneously. Surprisingly, when accounting for both size and location, location (regardless of size) determined rates of spontaneous passage (eg. small stones in the proximal ureter had the same chance of passage when compared to large stones in the proximal ureter). The only exception was the UVJ, where stone size still mattered. This finding is likely limited by the study’s small sample size for this stone location.

spontaneous passage rate of ureteral calculi as a function of stone size.jpg

spontaneous passage rate as a function of stone location.jpg

Bottomline: As expected, smaller stones pass more frequently than larger stones, and distal stones pass more frequently than proximal stones. However, other than UVJ stones, location seems to matter more in terms of rate of passage, regardless of stone size. This finding is likely limited by the study’s small sample size.

SMITH-BINDMAN ET AL.

This was an un-blinded randomized trial of 2,759 adult patients who were assigned to one of three arms: EM physician point of care ultrasound, radiology ultrasound, and CT. Patients in the study had to have a primary suspected diagnosis of kidney stones. Those considered high risk for other serious diagnoses (e.g., appendicitis, cholecystitis, abdominal aortic aneurysm) were excluded. Pregnant and severely obese patients were also excluded, as well as those with solitary kidneys, kidney transplants, or on hemodialysis. The study found no significant differences among the three groups in terms of missed high-risk diagnoses with complications (e.g., ruptured AAA, aortic dissection, ruptured appendicitis, diverticulitis with abscess or sepsis, ovarian torsion, bowel ischemia or perforation). There were also no significant differences among the three groups in terms of serious adverse events. Finally, there were no significant differences among the three groups in terms of other patient outcomes: ED bounce backs, hospital admissions, and pain scores. As expected, radiation exposure was lower in the ultrasound groups compared to the CT group.

Bottomline: Consider ultrasound as the initial diagnostic imaging test in this study population (primary suspected diagnosis of stone; not at high risk for other serious diagnoses; non-severely obese). Although CT is more sensitive than ultrasound in diagnosing stones, it did not translate into better patient outcomes.

LUCHS ET AL.

This was a retrospective study of 950 patients who had a CT and UA for suspected stone. The incidence of a negative UA for blood in patrients with actual stones on CT was 16%. Overall, hematuria was 84% sensitive, 48% specific for kidney stones on CT. The PPV was 72% and the NPV was 65%.

Bottomline: Hematuria is not an adequate screening tool for renal stones.

This month’s articles helped to clarify clinical questions regarding the diagnosis and expectant course of renal stones:

The STONE score can identify patients with a high probability of uncomplicated ureteral stone and absence of other important causes of symptoms (eg. diverticulitis, AAA, malignancy). This can help in our initial choice of imaging modality (ultrasound vs CT).
Smaller stones pass more frequently than larger stones, and distal stones pass more frequently than proximal stones.
Hematuria is not adequate as a screening tool for renal stones.