Oxidative Stress in Varicocele-Associated Male Infertility: Global Research Trends, Clinical Evidence, and Translational Gaps

Background: Varicocele is a common and potentially reversible condition associated with male infertility. Oxidative stress has been widely implicated in varicocele-related testicular dysfunction and impaired sperm quality. However, the development of this research field and the translational maturity of the available clinical evidence have not been systematically characterized. This study aimed to map the research landscape of oxidative stress in varicocele-associated male infertility from 2015 to 2025 and to assess clinical evidence domains, outcome levels, and translational gaps.

Methods: The Web of Science Core Collection was searched for the bibliometric analysis, which was conducted using VOSviewer and bibliometrix. PubMed, Embase, and Scopus were searched separately for human clinical and translational studies, while ClinicalTrials.gov was examined to characterize prospective research activity. Eligible studies were classified according to their primary evidence domain, highest centrally analyzed outcome level, and translational stage using prespecified criteria.

Results: The bibliometric analysis included 414 publications and showed an overall increase in research output. Research themes expanded from conventional redox markers and semen parameters to sperm DNA damage, mitochondrial dysfunction, inflammation, molecular profiling, and treatment-response assessment. The revised clinical evidence map included 142 studies. Molecular biomarkers/omics represented the largest evidence domain (51, 35.9%), followed by oxidative stress/redox biomarkers (28, 19.7%) and SDF/DFI/sperm DNA damage (27, 19.0%). Regarding outcome levels, 42 studies (29.6%) focused on biochemical/molecular outcomes, 49 (34.5%) on semen/sperm functional outcomes, 40 (28.2%) on SDF/DNA integrity outcomes, and only 11 (7.7%) on pregnancy, ART, or other fertility-related outcomes. Translational-stage assessment identified 73 association studies (51.4%), whereas only 3 studies (2.1%) were classified as replication/validation studies, indicating limited independent confirmation.

Conclusions: Research on oxidative stress in varicocele-associated male infertility has expanded in scope, but the clinical evidence remains dominated by association studies and laboratory or surrogate endpoints. Independent validation and patient-important reproductive outcomes are still uncommon. Greater assay standardization, predefined clinical thresholds, multicenter prospective validation, and greater use of pregnancy and live-birth outcomes are needed to narrow the gap between biological signals and clinically meaningful benefit.