Introduction and Objective: High-powered lasers have been hypothesized to cause kidney injury; however, no human studies have confirmed or quantified this damage. Our objective was to identify and quantify damage and explore factors affecting degree of injury in patients undergoing retrograde intrarenal surgery (RIRS) with thulium fiber laser (TFL) and Holmium:YAG (Ho:YAG) lasers. Methods: Patients undergoing RIRS for unilateral nonobstructing renal stones were randomized to receive lithotripsy with either a 60 W SuperPulse TFL or 120 W pulse-modulated Ho:YAG laser. A control group of patients undergoing RIRS without laser use were used for comparison. Urine samples were collected at 3 time points as follows: preoperative, 1 hour postoperative, and 10 days postoperative. Samples were analyzed using ELISA for key biomarkers-kidney injury molecule-1, neutrophil gelatinase-associated lipocalin (NGAL), and β2-microglobulin-normalized to urine creatinine. Primary outcome was the extent of renal injury based on biomarker elevation. Results: Ninety-one patients with similar baseline patient and stone characteristics were randomized (46 TFL, 45 Ho:YAG). Both lasers led to significant biomarker elevation, which trended toward but did not reach baseline by postoperative day 10. The Ho:YAG laser resulted in a sustained increase in NGAL at 10 days. Multivariate analysis demonstrated that injury is dose dependent on total laser energy used (p < 0.001, p = 0.006) and worse in older patients (p = 0.009) and in those with metabolic syndrome (p = 0.002), with slower recovery in both these groups, but not with the type of laser used. Multiple levels of the nephron are involved. Conclusions: There is notable kidney injury induced by both SuperPulse TFL and pulse-modulated Ho:YAG lasers in a dose-dependent manner, but the 2 lasers do not differ in the degree of injury. Injury occurs at multiple levels. Age and metabolic syndrome affect the amount of injury and recovery from injury. Further studies evaluating factors that can mitigate damage from high-energy lasers are needed.
