Flowing Differently: Exploratory Characterization of Menstrual Effluent Compared to Peripheral Blood

OBJECTIVE: This study aimed to characterize the immune cell and hormonal profile of menstrual effluent compared with paired peripheral blood. DESIGN: This descriptive, cross-sectional study collected menstrual effluent and processed it to isolate cellular and soluble fractions; peripheral blood was processed in parallel. Steroid hormones were quantified using immunoassays, immune cell populations were assessed by multiparameter flow cytometry, and cytokines and chemokines were measured using multiplex assays. SUBJECTS: Menstrual effluent and peripheral blood were collected from 13 healthy participants (excluded those using NSAIDs or hormonal contraception) following informed consent. EXPOSURE: None MAIN OUTCOME MEASURES: The immune cell and hormonal profiles of menstrual effluent and peripheral blood were the main outcome measures. RESULTS: T cells, alongside with decreased regulatory T cells, Natural Killer T (NKT) cells, and multiple B cell subsets. Cytokine analysis revealed multiple elevated cytokines in menstrual effluent, even after false discovery rate correction. CONCLUSIONS: Menstrual effluent is immunologically and hormonally distinct from peripheral blood, which may reflect inflammatory and tissue-repair activity. These findings contribute to understanding of normative baseline for menstrual effluent.