Serum inhibin B/follicle-stimulating hormone ratio as a predictor of testicular pathology in azoospermic men undergoing testicular sperm extraction: a retrospective study

Background Non-obstructive azoospermia (NOA) represents a severe form of male infertility characterized by impaired spermatogenesis and heterogeneous histopathological findings. Identifying candidate non-invasive biomarkers associated with underlying testicular histopathology before surgical sperm retrieval may provide additional information during preoperative evaluation and patient counseling. Introduction This study aimed to investigate the association of serum inhibin B (INHB), follicle-stimulating hormone (FSH), and their ratio (INHB/FSH) with histopathological groups in men undergoing microdissection testicular sperm extraction (micro-TESE). Materials and Methods A total of 73 men with NOA who underwent micro-TESE were retrospectively analyzed. Patients with obstructive azoospermia, endocrine disorders, or incomplete data were excluded. Serum FSH, luteinizing hormone (LH), testosterone, and INHB levels were measured within 2 months before surgery. Based on histopathological evaluation, patients were classified into five histopathological groups: Sertoli cell-only syndrome (SCOS), early maturation arrest (EMA), late maturation arrest (LMA), hypospermatogenesis (HSG), and normospermatogenesis (NS). The association between hormonal parameters and histopathological groups was evaluated using receiver operating characteristic (ROC) analysis and binary logistic regression. Results The INHB/FSH ratio differed significantly among the histopathological groups ( p < 0.001). Receiver operating characteristic analysis demonstrated moderate-to-high discriminative performance, with area under the curve values ranging from 0.77 to 0.91. In this exploratory cohort, provisional thresholds were observed across the histopathological groups, with lower values generally associated with SCOS, EMA, and LMA and higher values associated with HSG and NS. These findings should be considered hypothesis-generating and require internal and external validation before clinical application. Binary logistic regression demonstrated that higher INHB/FSH ratios were significantly associated with favorable sperm retrieval outcomes, with an odds ratio of 2.36 per 10-unit increase. Conclusions The serum INHB/FSH ratio was associated with histopathological groups and sperm retrieval outcomes in men with NOA undergoing micro-TESE. These findings suggest that the INHB/FSH ratio may warrant further investigation as a candidate non-invasive biomarker associated with histopathological groups in men with NOA.