Fibrin: Common Causes and Handling Methods

In routine biochemical testing, the blood collection tubes commonly used are yellow tubes containing blood clot activator and serum separation gel, or red tubes without separation gel but containing blood clot activator. Fibrin is often encountered, and it mainly occurs in the following three situations:

Blood Collection Tube Issues: Improper Use of Coagulants

If the amount or concentration of the blood clot activator in  tube is too high or too low, it can result in incomplete activation of fibrinogen by the coagulant. This prevents soluble fibrinogen from fully converting into insoluble fibrin aggregates, leading to unstable formation of fibrin clots. 

As a result, the blood coagulation process might produce a jelly-like serum.

As shown in the figure, blood clot activator play a crucial role in the blood coagulation process. Improper use of blood clot activator can lead to a jelly-like appearance of blood clots.

Improper blood collection procedures can also result in the appearance of jelly-like serum. If the blood is not allowed to fully coagulate before centrifugation, meaning it is centrifuged too soon after collection, red blood cells and activated platelets will detach from the fibrin network. 

This results in a lack of phospholipid surface, preventing fibrin from contracting.  After centrifugation, these fibrin fibers remain in the serum layer, creating a jelly-like appearance.

To avoid this situation, we should keep the blood for clot for at least 20 minutes after collection, waiting for it to fully coagulate before centrifugation.

Causes of sample abnormalities: Physiological and pathological factors

We also need to pay attention to abnormalities in the sample itself. For example, patients with myocardial infarction or those undergoing hemodialysis who are treated with heparin for anticoagulation may have jelly-like serum. 

This is because heparin’s anticoagulant effect is stronger in the body than outside it. It inhibits platelet aggregation and adhesion, enhances the activity of protein C, stimulates the endothelial cells of blood vessels to release fibrinolytic and anticoagulant substances, and strengthens the binding of antithrombin III with thrombin, thereby affecting blood coagulation.

In this case, even if the placement time is extended, the jelly-like serum cannot be improved. We should use a bamboo stick to stir the clot, allowing the serum to be squeezed out, and then use a pipette to aspirate the serum without the clot.

The appearance of jelly-like serum may be the result of a combination of factors, including the type of collection tube, the blood collection technique, and sample abnormalities. In practical work, we should pay attention to these details to ensure the accuracy of the test results.