What is the difference between plasma and serum?

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Plasma and serum are two elements of blood that are commonly thought to be the same thing, however, they are indeed different substances. In this article, we’ll go over what Plasma and Serum are and the key differences between them.

What is Plasma?

Plasma makes up about 55% of the overall blood volume. It is the liquid portion of blood and is 90% water. Other than water, plasma also contains fibrinogen (which contributes to the normal clotting of blood) and albumin (which acts to keep fluid in your bloodstream and prevent leaking into other tissues). The purpose of plasma in the blood is to transport all the proteins, nutrients, antibodies, hormones etc. all over the body. As the plasma races around the body, cells will deposit their waste into the plasma, which contributes to another job of the plasma: waste removal.

To be able to produce plasma from centrifugation, an anti-coagulant must be added to the blood. This is often pre-added when the blood sample is taken, meaning there is solution already in the tube to prevent clotting.

Plasma is the fluid that remains when clotting is prevented – meaning it retains its fibrinogen and albumin. This is important when your clotting and blood behaviour needs to be analysed.

What is Serum?

Put simply, serum is plasma minus the clotting factors and blood cells. During the process of removing the clotting factors (achieved by centrifugation), the protein fibrinogen as described above is converted to fibrin. Fibrin is an insoluble protein that is used to assist in the repair of tissue damage by forming a clot over the wound which acts to hinder the flow of blood.

Serum thus is the fluid that remains after coagulation, where the fibrin has been removed. This is used for blood typing and analysis.

What is the difference between Plasma and Serum?

A key difference between plasma and serum is that plasma is the natural fluid in the blood, and serum is the fluid minus clotting factors. While most of the components are the same for both plasma and serum, plasma contains fibrinogen which is absent in serum. Both plasma and serum can be extracted from blood with the use of a centrifuge but it’s worth noting that serum is obtained after the clotting of blood, while plasma can be obtained before the coagulation of the blood. Serum is mostly used for blood typing but is also used for diagnostic testing. Plasma on the other hand, is mostly used for blood-clotting related problems.

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