Thrombelastogram

A thrombelastogram provides information on platelet function, the number of platelets and the course of endogenous coagulation and fibrinolysis.

The principle is that a steel pin is suspended from a torsion wire in a cylindrical cuvette at 37 degrees Celsius. A small mirror is attached to this pin, which reflects the light of a light source on a film that is continuously transported at 2mm/min. The cuvette is slowly moved back and forth around its axis. After each deflection the cuvette stops for one second. The blood is filled into the space between the pen and the cuvette. The change in the rotation of the cuvette is transmitted to the pin and the film by the fibrin fiber that forms. The end position of the cuvette, in which it is stopped for one second at a time, produces continuous lines on the film.

A distinction is made between the reaction time R, i.e. the time during which the blood contained in the cuvette does not clot and the movement of the cuvette is not transferred to the plunger. When fibrin is formed, shear forces are transmitted to the plunger and the torsion filament. The fibrin formation time is the time that elapses from the beginning of the movement of the plunger up to an amplitude of 20 mm.

The maximum elasticity of the thrombus is calculated from the maximum amplitude x 100: 100 - maximum amplitude. When fibrinolysis begins, the maximum amplitude decreases again.

If the reaction and fibrin formation time is prolonged and the maximum elasticity of the thrombus is reduced, there is an urgent suspicion of a factor deficiency.
If the reaction time and coagulation time are shortened and the maximum elasticity is increased, this indicates hypercoagulability. If the amplitude decreases rapidly, fibrinolysis is increased. If the maximum elasticity remains shortened over the entire observation period, thrombopenia is present.

Platelet function values are determined from citrate blood. The blood must be transported at 22 degrees Celsius and processed within two hours. The blood is anticoagulated with sodium citrate in a ratio of nine parts blood and one part Na-citrate 0.11 mol/l.

1. HA Neumann (2014) The coagulation system. ABW-Science Publishing House GmbH Berlin.