The effect of hematocrit, fibrinogen concentration and temperature on the kinetics of clot formation of whole blood

BACKGROUND: Dynamic mechanical analysis of blood clots can be used to detect the coagulability of blood. OBJECTIVE: We investigated the kinetics of clot formation by changing several blood components, and we looked into the clot 'signature' at its equilibrium state by using viscoelastic and dielectric protocols. METHODS: Oscillating shear rheometry, ROTEM, and a dielectro-rheological device was used. RESULTS: In fibrinogen- spiked samples we found the classical high clotting ability: shortened onset, faster rate of clotting, and higher plateau stiffness. Electron microscopy explained the gain of stiffness. Incorporated RBCs weakened the clots. Reduction of temperature during the clotting process supported the development of high moduli by providing more time for fiber assembly. But at low HCT, clot firmness could be increased by elevating the temperature from 32 to 37°C. In contrast, when the fibrinogen concentration was modified, acceleration of clotting via temperature always reduced clot stiffness, whatever the initial fibrinogen concentration. Electrical resistance increased continuously during clotting; loss tangent (D) (relaxation frequency 249 kHz) decreased when clots became denser: fewer dipoles contributed to the relaxation process. The relaxation peak (Dmax) shifted to lower frequencies at higher platelet count. CONCLUSION: Increasing temperature accelerates clot formation but weakens clots. Rheometry and ROTEM correlate well.