The Diagnostic Accuracy of Reduced-Dose CT of the Kidneys, Ureters, and Bladder in the Evaluation of Renal Colic.

Non-contrast CT of the kidneys, ureters, and bladder (CT KUB) is the reference standard for suspected renal colic, but radiation exposure is a concern. Reduced-dose CT KUB protocols have been developed to minimise risk, and multiple systematic reviews have assessed their diagnostic accuracy. Our objective was to evaluate the diagnostic performance of low-dose (LD) and ultra-LD (ULD) CT KUB for suspected urolithiasis and to evaluate the methodological quality of systematic reviews written on this topic. A systematic search in June 2025 was conducted on MEDLINE, Embase, PubMed, and the Cochrane Library from inception until the time of search, yielding 1,357 results, with 1,318 remaining after de-duplication. Three systematic reviews were eligible. Data were extracted on study scope, populations, definitions of LD/ULD dose, accuracy outcomes, and review quality. Risk of bias was appraised using risk of bias in systematic reviews (ROBIS). The three included reviews synthesised between six and 12 primary diagnostic accuracy studies (sample sizes: 903-1,529 participants) and were published in the mid-to-late 2010s. Pooled estimates from one review demonstrated high diagnostic performance of LD and ULD CT KUB (ULD: sensitivity 95%, specificity 97%; LD: sensitivity 92%, specificity 97%). The remaining reviews provided narrative syntheses, consistently reporting sensitivities and specificities above 85%, though diagnostic performance was reduced in obese patients and for stones <3 mm. All reviews highlighted the potential to detect alternative diagnoses. ROBIS identified one review at low risk of bias, one at moderate risk (due to heterogeneous reference standards and language restrictions), and one at high risk (no primary study quality appraisal). Existing systematic reviews consistently support reduced-dose CT KUB as highly accurate for diagnosing urolithiasis, with performance approaching standard-dose CT, though limitations exist in obese patients and for very small stones. Methodological quality of the reviews was variable. Further high-quality reviews using standardised methods are warranted to refine estimates and assess generalisability.