Introduction: The natural progression of asymptomatic kidney stones remains unclear. Such knowledge may promote value-aligned care for patients and reduce potentially unnecessary procedures. We sought to evaluate the natural history of asymptomatic kidney stones in adults undergoing active surveillance. Materials and Methods: Using themes of "Kidney Stone" and "Active Surveillance," we performed a systematic review by searching for studies in MEDLINE, all Cochrane libraries, EMBASE, Cumulative Index to Nursing and Allied Health Literature, BIOSIS, Scopus, and Web of Science from inception through October 2017-in addition to ClinicalTrials.gov, American Urological Association Annual Meeting abstracts (2014-2017), Google Scholar, and references of included studies and prior reviews. Two blinded reviewers independently extracted data and assessed methodological quality. We qualitatively summarized rates of surgical intervention (primary outcome), spontaneous stone passage, symptom development, and stone growth. We assessed the relationship between surveillance duration and rate of surgical intervention with Pearson's correlation coefficient. Results: Of 7034 unique records, 13 studies met final eligibility criteria. There was substantial variation in reported rates of surgical intervention from 6/85 (7.1%) to 80/301 (26.6%), spontaneous stone passage from 1/32 (3.1%) to 101/347 (29.1%), symptom development from 7/96 (7.3%) to 231/300 (77.0%), and stone growth from 5/96 (5.2%) to 33/50 (66.0%). Mean surveillance duration spanned from 11.3 to 80 months (range 2-180 months). Longer mean duration of surveillance did not correlate with an increase in surgical intervention rate across studies (n = 13, r = 0.01, p = 0.98), and this finding persisted when restricting analysis to observational studies (n = 9, r = 0.12, p = 0.76). Conclusions: Active surveillance appears to be a durable strategy for a majority of patients with asymptomatic kidney stones, as there was no increase in failure of watchful waiting despite increasing duration of surveillance. Higher quality studies are needed to ascertain which patients may benefit most from active surveillance.
Keywords: kidney calculi; systematic review; watchful waiting.