Molecular and Conventional Tests in Onychomycosis: A Systematic Review of Paired Diagnostic Discordance and Clinical Interpretation

Discordant laboratory results complicate the diagnosis of onychomycosis because molecular assays, culture, microscopy, and histopathology detect different features of fungal infection.We systematically reviewed human nail studies comparing molecular testing of primary nail material with conventional methods.PubMed was searched without language or publication-date restrictions on August 29, 2026, and updated on September 20, 2026.Six supplementary Google Scholar searches and backward and forward citation searches were also performed.Of 102 reports sought, 101 were assessed and 97 were included; one could not be retrieved.Seventy-six reports provided paired 2 × 2 data, and 21 provided marginal or narrative evidence.The 174 extracted comparisons were summarized descriptively.In the initial exploratory set of 40 culture comparisons from 37 reports, molecular-only positives outnumbered culture-only positives in 38 comparisons.The median net detection difference was 16.1 percentage points (IQR, 11.5-22.9).A broader post hoc analysis selecting one comparison per eligible report included 50 reports and yielded a median of 16.6 points (IQR, 10.4-28.1);excluding potentially overlapping cohorts yielded 16.2 points.Microscopy or histopathology yielded more additional positives in four of six exploratory structural comparisons.Selection bias, previous treatment, differences in assay coverage, and incomplete verification limited interpretation.The single-reviewer process, PubMed-centered search, and post hoc analytic decisions further limit the synthesis.Molecular assays frequently detected fungal targets in culture-negative nails, but these additional findings cannot be equated with viable infection or superior diagnostic accuracy.Discordant results require assessment of the organism, assay coverage, specimen quality, treatment history, and corroborating evidence.These data support the complementary use of diagnostic methods; they do not establish a universal detection gain or a validated treatment algorithm.