Sex-related molecular phenotypes in anxiety-depressive disorders: a machine learning analysis of routine blood biomarkers.

Background: Anxiety disorders and depressive disorders are the most prevalent mental disorders worldwide. Their diagnosis has long relied on clinical symptom assessment, and objective blood-based biomarkers remain lacking. Sex is a critical risk factor for these disorders; however, sex-specific divergence in blood biochemical profiles has yet to be systematically characterized. Methods: This retrospective study enrolled 778 patients diagnosed with anxiety-depressive state at China-Japan Friendship Hospital. Demographic data, complete blood count parameters, and blood biochemical parameters were collected. Following missing value processing and multiple imputation, Mann-Whitney U tests were applied to identify sex-differentially expressed biomarkers. A random forest classifier was constructed to evaluate the discriminative capacity of combined multi-marker panels, with model performance comprehensively assessed through receiver operating characteristic curve analysis, SHAP-based explainability analysis, and multi-classifier probability projection. Age-stratified analyses were performed with a threshold of 50 years to explore the potential modifying effect of age on sex differences. Results: Several biomarkers exhibiting significant differences between males and females were identified (FDR < 0.05), among which creatinine, hemoglobin, hematocrit, red blood cell count, and uric acid demonstrated the largest effect sizes. The random forest model achieved an area under the receiver operating characteristic curve of 0.902 on the independent test set. Multi-classifier probability projection following hyperparameter tuning yielded a Silhouette coefficient of 0.464 in the two-dimensional space, with permutational multivariate analysis of variance confirming highly significant centroid differences between groups (p < 0.001). Age-stratified analysis using hemoglobin as an example revealed that levels in males were significantly higher than those in females across both age strata, with the magnitude of the sex difference attenuated in the ≥50-year group compared with the <50-year group. Conclusions: Robust sex-related signals are embedded in routine blood biochemical markers. Although complete separation is difficult to achieve under unsupervised dimensionality reduction, these signals can be efficiently integrated through ensemble learning algorithms. This study provides a molecular phenotypic basis related to sex in patients with anxiety-depressive state and underscores the importance of fully considering sex as a variable in clinical laboratory testing.