At our institution we currently offer a quantitative D-dimer using the Sysmex CA-1500, and a fibrin degredation products assay (FDP, Remel Thrombo-Wellco Test). What can I say to our physicians to convince them to allow us to stop offering the FDP, and to rely on the D-dimer (along with the platelet count, PT, PTT and fibrinogen) in the evaluation of DIC? Thank you for your time. Nicole Frantti
Nicole, many writers, including me, have perpetuated the myth that you can use FDPs in tandem with the D-dimer assay to distinguish between disseminated intravascular coagulation (DIC) and primary (systemic) fibrinolysis. In theory, no D-dimer forms in primary fibrinolysis because without activation of the coagulation mechanism, there can be no factor XIII-catalyzed fibrin crosslinking. The theory seems sound, but in practice D-dimer elevation occurs in relationship to all inflammatory conditions, and rises during tissue plasminogen activator (TPA) therapy to greater than expected levels. Further, many experts claim there is really no such thing as primary fibrinolysis.
Consequently, in all circumstances where the FDP is expected to rise, the D-dimer will also rise. Further, current quantitative D-dimer assays are more precise and reproducible than the semi-quantitative FDP kit because fibrinogen cross-reacts and causes false positives. This is why you have to collect the FDP specimen in a special tube with thrombin, to speedily clot the specimen and take fibrinogen out of the serum.
You’ll need a reference to convince your clinicians to discontinue ordering FDPs. I recommend Chapter 23, Physiologic Regulation of Fibrinolysis in Colman RW, Marder VJ, Clowes AW, George JN, Goldhaber SZ. Hemostasis and Thrombosis: Basic Principles and Clinical Practice, 5th Edition, 2006, Saunders. In particular, see page 429, “Clinical Relevance of Degradation Products.” The comments there are authoritatively referenced. Geo.