Background: Viscoelastic tests such as functional fibrinogen polymerization assays (FFPAs) in thrombelastography (TEG(®)) or thromboelastometry (ROTEM(®)) measure the elasticity of extrinsically activated clotting under conditions of platelet inhibition. There are no reports on whether components of the FFPAs have any effects on fibrin polymerization, aside from the effects of platelet inhibition.
Methods: Using various platelet-free plasma (PFP) preparations, we compared the extrinsically activated EXTEM thromboelastometric assay with 3 FFPAs: FIBTEM, FIBTEM PLUS, and the Functional Fibrinogen Test(®) (FFTEG). These FFPAs activate coagulation extrinsically but additionally inhibit platelet function. We used calibration plasma (Instrumentation Laboratory and Siemens), pooled fresh-frozen plasma (Octaplas) and freshly prepared PFP from a healthy volunteer. EXTEM and all FFPAs were run in parallel on a ROTEM device.
Results: Median (interquartile range) maximum clot firmness (MCF) values for all plasma preparations were: 20.5 mm (17.25-22.0 mm) in EXTEM, 23.0 mm (18.5-24.0 mm) in FIBTEM, 23.0 mm (18.25-24.75 mm) in FIBTEM PLUS, and 18.0 mm (16.0-19.0 mm) in FFTEG. Compared with EXTEM, FIBTEM and FIBTEM PLUS (P < 0.01) showed increased MCF values whereas FFTEG (P < 0.001) showed decreased MCF values. Further experiments in PFP showed that the platelet inhibitors used in the FFPAs (cytochalasin D or the glycoprotein-IIb/IIIa inhibitor abciximab) were not causing these alterations in MCF. However, reducing the activating tissue factor concentration (by diluting the extrinsic assay) decreased the MCF.
Conclusions: We speculate that FIBTEM and FIBTEM PLUS may contain stabilizing agents that enhance fibrin polymerization whereas FFTEG might contain less tissue factor than the ROTEM assays.