Is it possible to make a common reference standard for D‐dimer measurements? Communication from the ISTH SSC Subcommittee on Fibrinolysis

BACKGROUND: D‐dimer antigen is a heterogeneous mixture of fibrin degradation products that when present at high levels in plasma indicate ongoing coagulation and fibrinolysis. The heterogeneous nature of the target D‐dimer antigen and the variety of assay systems means that it is difficult to compare results from different methods. OBJECTIVES: To identify a universally agreed D‐dimer standard that could help harmonize results from different methods. METHODS: A pool of patient plasma with high D‐dimer levels was freeze‐dried and investigated as a long‐term World Health Organization international standard for D‐dimer. Fibrin degradation products from clot lysis reactions were also freeze‐dried in various formulations and investigated in commutability studies with patient plasma. RESULTS: Problems of instability of D‐dimer plasma emerged suggesting loss of reactivity after freeze‐drying and storage at −20°C of 10%–18% per year. Freeze‐dried fibrin degradation products added to plasma were also unstable, but the sugar trehalose was found to improve stability. However, this preparation was not suitable as a standard in widely used assay platforms. Previous studies suggest fibrin degradation products are prone to structural rearrangements and amyloid formation, which may explain the instability of candidate D‐dimer standards. CONCLUSIONS: The known difficulties of D‐dimer standardization are compounded by instability of D‐dimer antigen after freeze‐drying, described in this report. Fibrin degradation products added to plasma and stabilized by trehalose are not suitable as a standard for D‐dimer measurement harmonization. Trehalose stabilization of pooled patient plasma containing high D‐dimer levels may produce a useful standard, but this requires confirmation.