Discriminative Performance of Semen, Hormonal, and Clinical Parameters for Male Fertility Based on WHO 2021 Reference Values

Background: The diagnosis of male infertility often relies solely on semen analysis, despite its well-recognized limitations. The clinical utility of the updated World Health Organization (WHO) 2021 reference standards, especially when integrated with other clinical markers, requires validation. This study aimed to evaluate the discriminative performance of semen parameters, testicular volume, and hormonal profiles in differentiating fertile from infertile men using WHO 2021 criteria. Methods: This retrospective study included 417 men (315 infertile, 102 fertile). All parameters were re-evaluated according to WHO 2021 standards. Receiver operating characteristic (ROC) curve analysis and multivariable logistic regression were performed to identify independent predictors and construct an integrated predictive model. Results: Fertile men had significantly better semen parameters and larger testicular volume, while infertile men showed higher follicle-stimulating hormone (FSH) and prolactin, and lower testosterone (p < 0.05). Sperm concentration (area under the curve [AUC] = 0.984) and morphology (AUC = 0.913) showed the strongest discrimination. Multivariable analysis identified sperm concentration, morphology, mean testicular volume, and FSH as independent predictors of fertility status. The combined model demonstrated excellent performance (AUC = 0.994; 95% confidence interval [CI]: 0.988–0.999), confirmed by Bootstrap internal validation (optimism-corrected AUC = 0.992). Sensitivity analyses showed high discriminative power across all phenotypes, including normozoospermic infertility (AUC = 0.921). Conclusion: Sperm concentration and morphology remain the most robust indicators of male fertility within the WHO 2021 framework. The integration of clinical, hormonal, and semen parameters improved predictive accuracy and supports a multidimensional approach to the evaluation of male infertility, while confirming the applicability of WHO 2021 reference standards in this population.