Then, why the normal collection of serum tube (without additives or with coagulant) specimens also formed fibrin clots in vitro, but did not degrade to generate a large amount of FDP and D-dimer? This depends on the serum tube. What happened after the specimen was collected: First, there is no large amount of tPA entering the blood; second, even if a small amount of tPA enters the blood, the free tPA will be bound by PAI-1 and lose its activity in about 5 minutes before it attaches to the fibrin. At this time, there is often no fibrin formation in the serum tube without additives or with coagulant. It takes more than ten minutes for blood without additives to coagulate naturally, while blood with coagulant (usually silicon powder) starts internally. It also takes more than 5 minutes to form fibrin from the blood coagulation pathway. In addition, the fibrinolytic activity at room temperature in vitro will also be affected.

Let’s talk about the thromboelastogram again along this topic: you can understand that the blood clot in the serum tube is not easily degraded, and you can understand why the thromboelastogram test (TEG) is not sensitive to reflect hyperfibrinolysis-both situations It is similar, of course, the temperature during the TEG test can be maintained at 37 degrees. If TEG is more sensitive to reflect the fibrinolysis status, one way is to add tPA in the in vitro TEG experiment, but there are still standardization problems and there is no universal application; in addition, it can be measured at the bedside immediately after sampling, but the actual effect is also very limited. A traditional and more effective test for evaluating fibrinolytic activity is the dissolution time of euglobulin. The reason for its sensitivity is higher than that of TEG. In the test, the anti-plasmin is removed by adjusting the pH value and centrifugation, but the test consumes It takes a long time and is relatively rough, and it is rarely carried out in laboratories.