Plasma protein profiles in Bleeding Disorder of Unknown Cause

In over half of patients with mild to moderate clinically relevant bleeding, the etiology remains unknown, and patients are classified as having bleeding disorders of unknown cause (BDUC).

To identify alterations within and beyond the classical hemostatic system and characterize the plasma proteome in BDUC.

Plasma samples of two blood draws from patients (n=105) with BDUC from the Vienna Bleeding Biobank and a reference population (n=118) were analyzed using targeted and unbiased mass spectrometry-based proteomics. Protein levels were assessed for associations with bleeding phenotype, functional laboratory tests and clinical characteristics, and individual signatures were examined across two blood draws.

Targeted and discovery-based proteomics demonstrated similar distributions of coagulation and fibrinolytic proteins in BDUC compared to reference. Plasma proteome profiles were predominantly shaped by female sex and ABO blood group, while only limited associations were observed with bleeding severity. Among hemostatic proteins, tissue factor pathway inhibitor, von Willebrand factor and protein Z exhibited the greatest inter-individual variability, although to a similar extent as in the reference population. Global plasma protein levels were consistent across blood draws, and one-versus-all analysis identified predominantly acute-phase and sex hormone-related proteins, with limited alterations in the hemostatic system.

Proteomic profiles in BDUC were within normal ranges at steady state, suggesting that unexplained bleeding is unlikely to result from isolated quantitative alterations in hemostatic plasma proteins. These findings highlight the need for functional omics approaches and multi-compartment analyses beyond plasma to uncover the mechanisms underlying unexplained bleeding.