Accuracy of Low-Dose and Ultra-Low-Dose CT for Nephrolithiasis in Obesity: A Multicenter Review.

OBJECTIVE: To evaluate the diagnostic accuracy of low-dose (LD) and ultra-low-dose (ULD) computed tomography (CT) scan for stone identification in obese patients compared to conventional-dose CT. METHODS: A review of patients undergoing CT scans for kidney or ureteral stones at two academic institutions was conducted. Patients with body mass index (BMI) >30 kg/m2 and both a conventional and LD CT within 100 days of each other were included. LD was defined as <4 millisieverts (mSv) and ULD as <1.9 mSv. Renal units with interval treatment or documented stone passage were excluded. CTs were reviewed by board-certified radiologists. RESULTS: Fifty-two patients met inclusion criteria with mean BMI of 36.2 kg/m2 (range: 30.2-63.8). The combined average effective dose of LD and ULD CT was significantly lower than conventional CT (2.3 vs 14.9 mSv; p<0.001), an 85% reduction. LD and ULD CT detected 92/96 stones >2 mm (96% sensitivity) and 95/115 stones overall (83% sensitivity). All stones missed were ≤4 mm in size. LD CT BMI-stratified analysis demonstrated 100% sensitivity for stones >2 mm for BMI 30-35 and >40 kg/m2, and 90% for BMI 35-40 kg/m2. ULD CT demonstrated 100% sensitivity for stones >2 mm for BMI 30-35 kg/m2. CONCLUSION: Overall, LD and ULD CT in obese patients accurately identified stones >2 mm with 96% sensitivity, while reducing radiation dose by 85%. This multicenter study supports the accuracy of LD CT for stone identification in noninfected obese patients across BMI subgroups, with ULD CT best reserved for patients with BMI 30-35 kg/m2.