Calcium Phosphate Composition Affects Ureteroscopic Laser Lithotripsy

The effects of stone composition on transurethral lithotripsy (TUL) have not been sufficiently elucidated. The purpose of this study was to identify how calcium phosphate stone composition impacts TUL. Two hundred eighty-nine cases of semi-rigid and/or flexible TUL for upper urinary tract calculi were reviewed retrospectively. Inclusion criteria were a preoperative assessment by noncontrast computed tomography (NCCT) and a stone composition analysis. Small stones and those without calcium composition were excluded. Stone core radiodensity (SCR) was measured by taking the average of the upper 3 of 5 points in the proximity of the center of the stone on NCCT. Fifty-three patients with calcium phosphate composition (CaP) and 118 patients with calcium oxalate and without phosphate composition were eligible for analysis. SCR was significantly higher in the CaP group (p<0.01). The CaP patient group needed a significantly longer operation time (p=0.014) and more laser energy (p=0.085), and tended to have a lower rate of complete lithotripsy (p=0.096) and higher incidence of postoperative pyelonephritis (p=0.181). Stones containing calcium phosphate are harder, demand more laser energy, and require a longer operating time. NCCT evaluation can estimate stone composition preoperatively, and may be a useful tool for predicting operative outcomes.