Sperm morphology indices as exploratory screening tools for elevated DNA fragmentation: a single-centre correlation and threshold derivation study

BACKGROUND: Sperm morphology assessment remains a routine component of semen analysis, yet its relationship with sperm DNA fragmentation at the level of individual morphological indices is incompletely characterised. This study evaluated correlations between the Teratozoospermia Index (TZI), Sperm Deformity Index (SDI), and Multiple Anomalies Index (MAI) with the DNA Fragmentation Index (DFI), deriving exploratory thresholds to identify men at risk of elevated DNA fragmentation (DFI > 20%). METHODS: A retrospective analysis was conducted on 135 semen samples from men aged 20-55 years attending a university andrology centre. Morphology was assessed on Papanicolaou-stained smears; TZI, SDI, and MAI were calculated manually. DNA fragmentation was measured using the GC-SCD-20 kit. Pearson correlation and receiver operating characteristic (ROC) analysis with Youden-optimised thresholds were performed. RESULTS: All three indices showed statistically significant, weak positive correlations with DFI: TZI (r = 0.263, p = 0.001), SDI (r = 0.290, p = 0.004), and MAI (r = 0.371, p < 0.001). ROC analysis demonstrated modest discriminatory performance: AUC values of 0.645, 0.620, and 0.680 respectively. At thresholds of TZI > 1.85, SDI > 2.42, and MAI > 2.53, sensitivity ranged from 82% to 90% with specificity of 44-53%. CONCLUSION: TZI, SDI, and MAI correlate weakly but significantly with DFI and demonstrate a high-sensitivity, low-specificity screening profile. These thresholds are exploratory, derived from a single cohort, and require prospective validation in larger independent studies before clinical application. They should be regarded as adjunctive tools within routine semen analysis and cannot substitute for direct DNA fragmentation testing.