Purpose or Case Report: To determine the diagnostic performance of renal ultrasound for diagnosing nephrolithiasis in children using a clinical effectiveness approach.
Methods & Materials: Institutional review board approval with a waiver of informed consent was obtained for this retrospective, HIPAA-complaint investigation. Billing records and imaging reports were used to identify children (≤18 years-old) evaluated for nephrolithiasis by both ultrasound and unenhanced CT within 24 hours between March 2012 and March 2017. Imaging reports were reviewed for presence, number, size, and location of kidney stones. Diagnostic performance of ultrasound (reference standard = CT) was calculated per renal unit (left/right kidney) and per renal sector (four sectors per kidney). For sector analysis, ultrasound was considered truly positive if a stone was identified at CT in the same or an adjacent sector.
Results: There were 68 renal stones by CT in 30/69 patients (43%). Mean patient age was 14.7±3.6 years, and 35 were boys. For detecting nephrolithiasis in any kidney, ultrasound was 66.7% (48.8-80.8%) sensitive and 97.4% (86.8-99.9%) specific (positive predictive value [PPV]=95.2% [77.3-99.8%], negative predictive value [NPV]=79.2% [65.7-88.3%], and positive likelihood ratio [PLR]=26.0). Per renal sector, ultrasound was 59.7% (46.7-71.4%) sensitive and 97.4% (95.5-98.5%) specific (PPV=72.3% [58.2-83.1%], NPV=95.4% [93.2-96.9%], PLR=22.5). Of the 30 stones not detected by ultrasound, only three were >3 mm at CT.
Conclusions: In clinical practice, ultrasound has high specificity for detecting nephrolithiasis in children but only moderate sensitivity and false negatives are common.