Diagnostic Accuracy of Low-Dose CT versus Standard-Dose CT in the Detection of Urolithiasis

Abstract

Non-contrast CT is the reference imaging test for urolithiasis, but the associated radiation dose is a concern, especially in young patients who may undergo repeated scans. This study assessed the diagnostic accuracy of low-dose CT (LDCT) against standard-dose CT (SDCT) for the detection of urinary tract stones. In this prospective comparative study at Al-Hussein Teaching Hospital in Al-Nasiriyah (Thi-Qar Province, Iraq), 150 adults with suspected renal colic underwent both LDCT and SDCT in the same session. SDCT served as the reference standard. Two radiologists, blinded to the reference reading, independently interpreted the LDCT images. Per-patient and per-stone sensitivity, specificity, predictive values, and accuracy were calculated with 95% confidence intervals (CI), with subgroup analysis by stone size and body mass index (BMI) and comparison of effective radiation dose. Reporting followed the STARD 2015 guideline. Urolithiasis was present in 102 of 150 patients (68%). LDCT achieved a per-patient sensitivity of 95.1% (95% CI 88.9–98.4), specificity of 97.9% (95% CI 89.1–99.9), and accuracy of 96.0%. Per-stone sensitivity was 94.0% overall but fell sharply for stones smaller than 3 mm (69.2% vs 98.6% for ≥ 3 mm; p < 0.001) and was lower in patients with BMI ≥ 30 (88.9% vs 97.2%). Inter-observer agreement was excellent (κ = 0.88). The mean effective dose was 76% lower with LDCT (1.9 ± 0.5 vs 8.1 ± 1.8 mSv; p < 0.001). LDCT detected urolithiasis with high accuracy at roughly one-quarter of the radiation dose of SDCT and can serve as the first-line protocol for suspected renal colic. Its main limitation is reduced sensitivity for sub-3-mm stones and in obese patients, where a standard-dose protocol should be considered.