Menstrual blood (MB) is an accessible, non-invasive biospecimen uniquely reflective of the endometrial environment. Unlike peripheral blood, MB contains exfoliated endometrial stromal and epithelial cells, immune cells, cytokines, extracellular matrix components, and a diverse proteomic and lipidomic profile—mirroring the intrauterine milieu during menstruation. Studies have demonstrated that MB from individuals with endometriosis shows distinct molecular alterations, including elevated expression of estrogen-regulating genes (e.g., aromatase, SF-1, and HSD17B2) [1], differential lipid signatures [2], and increased levels of proteins such as CXCL5 and IL1RN [3]. Sensory nerve fibers, strongly associated with pain in endometriosis, have also been detected in eutopic endometrial tissue [4], suggesting altered tissue composition that may be traceable in MB. MB contains over 350 proteins not found in peripheral blood or vaginal secretions [5], indicating high diagnostic potential. These approaches respond to the clinical need for earlier non-invasive diagnostics in adolescents and young women experiencing dysmenorrhea—a population often overlooked or delayed in diagnosis [6]. Additionally, efforts to detect systemic biomarkers in peripheral blood have shown promise but limited specificity and practicality, further justifying MB as a superior alternative [7].