SERPIND1 (serpin family D member 1), also known as heparin cofactor II, is a serine protease inhibitor located on chromosome 22 that functions primarily in the coagulation and immune response pathways 1. As a glycosaminoglycan-binding serpin, SERPIND1 requires cofactors such as heparin and dermatan sulfate to achieve physiologically relevant inhibition rates of target proteases, with GAG binding potentially accelerating inhibition up to 10,000-fold 1. In vitro, SERPIND1 shows negligible inhibition of thrombin and tissue plasminogen activator, and no inhibition of factor Xa. Clinically, SERPIND1 deficiency causes thrombophilia, reflecting its essential role in coagulation regulation 1. Beyond coagulation, emerging evidence indicates broader pathophysiological significance. SERPIND1 expression is associated with survival outcomes in systemic sclerosis-related pulmonary hypertension, where elevated levels correlate with better prognosis 2. In glaucoma pathogenesis, SERPIND1 is upregulated and implicated in eye transparency and glucose metabolism 3. Additionally, SERPIND1 functions as an immune-related biomarker, with differential expression patterns observed in juvenile gout 4, endometrial carcinoma 5, and lung adenocarcinoma 6, suggesting roles in inflammatory and neoplastic disease processes. These findings establish SERPIND1 as a multifunctional protease inhibitor with implications extending beyond hemostasis to ocular health, systemic inflammation, and cancer immunology.