Diagnostic Criteria for Kidney Stones

Key Diagnostic Features

The American College of Radiology recommends the addition of color Doppler with assessment of twinkling artifact for small renal stones (<5 mm), with reported sensitivity as high as 99% 1
The presence of hydronephrosis has up to 100% sensitivity and 90% specificity for ureteral obstruction, though this may not be present with non-obstructing renal stones 1
Within the first 2 hours of presentation, secondary signs of obstruction may not have developed yet 1

Gray-scale ultrasound alone has only 24-57% sensitivity for detecting renal calculi compared to CT 1, 2
Ultrasound tends to overestimate stone size, particularly for stones ≤5 mm 1

If clinical suspicion remains high despite equivocal ultrasound findings, noncontrast CT is the reference standard with 97% sensitivity 3
Low-dose CT protocols maintain 97% sensitivity while reducing radiation exposure 4

Small stones ≤5 mm have lower probability of causing significant obstruction, but approximately 16-20% still require surgical intervention within 5 years 5
The absence of hydronephrosis on ultrasound makes the presence of a larger obstructing stone (>5 mm) less likely 1