Purpose: We investigated the clinical efficacy of the Triple D score (TrD-S) on stone-free rate (SFR) prediction following shockwave lithotripsy (SWL) for renal stones 10-20 mm in diameter and modified the scoring system to improve outcome prediction.
Methods: We retrospectively examined clinical data from the medical records of 226 consecutive patients who underwent SWL for 10-20 mm kidney stones. The TrD-S was calculated according to the cutoffs of < 150 mm3 for stone volume, < 600 Hounsfield unit for stone density, and < 12 cm for skin-to-stone distance on computed tomography. The Quadruple D score was defined as the sum of the TrD-S and stone location (0/1 point for intrarenal stone distribution at lower/non-lower poles, respectively). Complete clearance 3 months after the final SWL was considered the stone-free status.
Results: The residual group (n = 102) had significantly older age, larger stones, higher stone density, higher lower-pole stone incidence, and lower TrD-S than the stone-free group (n = 124). In the multivariate analysis, age, TrD-S, and non-lower-pole stones independently predicted the SFR. The TrD-Ss of 0, 1, 2, and 3 points showed SFRs of 40.0%, 51.9%, 73.0%, and 100.0%, respectively. The Quadruple D scores of 0, 1, 2, 3, and 4 points showed SFRs of 0.0%, 37.9%, 54.5%, 84.4%, and 100.0%, respectively, with better prediction accuracy than the TrD-S (p = 0.01).
Conclusions: The TrD-S is successfully validated for use in Japanese patients with 10-20-mm renal stones. Simple addition of the stone location to the TrD-S could reinforce SFR prediction after SWL.
Keywords: Lower pole; Renal stone; Shockwave lithotripsy; Triple D score.