Difference Between Plasma and Serum

Plasma vs Serum

A common misconception among people is that plasma and serum is the same thing. They are two different substances with a common precursor solution and containing constituents, which makes them unique and required for various medical procedures. The common precursor is blood, and the level of purification of the blood is the determinant of plasma and serum. When we consider blood, it is made up of red blood cells, white blood cells, platelets, proteins, and a watery substance. The above mentioned two substances are important in therapeutic and diagnostic procedures in humans, and currently various research are being conducted regarding the specific nature of these substances.

What is Plasma?

Plasma is the basic watery part of the blood. We are able to observe plasma, if we stand a column of blood for about one hour, we can see the precipitation of red cells and white cells with a supernatant straw colored liquid. This liquid is the plasma. Plasma contains fibrinogen, an important factor in the clotting process and other major factors of clotting. Thus, on standing this straw colored liquid tends to clump. This plasma can be spun, so the protein materials with heavier masses tend to precipitate down, leaving better purified plasma. Plasma is required for diagnostic investigation and especially for therapeutic transfusions in people, who are hypovolemic, deficient in clotting factors, etc. A lesser clot prone plasma is available as cryo poor plasma (CPP), and the removed clotting agents are used in the treatment of hemophiliacs as cryo precipitate.

What is Serum?

Serum is plasma without the clotting factors, mainly the fibrinogen. So serum, on standing does not clot. Usually, to acquire serum, all clotting agents in plasma are removed through progressive centrifuging, or we can get a blood sample and after allowing it to clot, the supernatant is taken. Serum includes all the other electrolytes, proteins not used in the clotting process, drugs and toxins. Human serum is usually used for the purpose of diagnostic testing. Other animal seras are used as anti venom, anti toxins, and vaccinations.

What is the difference between Plasma and Serum?

Both plasma and serum are derivatives of blood. Both contain electrolytes, other proteins, drugs, hormones and toxins. Both can be acquired from centrifugation and purity depends on the duration and the frequency of this process. Both can be used for diagnostic and therapeutic purposes. But plasma is serum with fibrinogen and clotting factors. So plasma tends to discolor on standing, whereas serum does not. Separation of plasma is relatively easy and inexpensive, whereas separation of serum requires higher levels of expertise and expenses. Plasma is most commonly used for therapeutic purposes where, either the full plasma (Fresh frozen plasma), clotting factor removed (Cryo poor plasma) or the clotting factors itself (Cryo precipitate) can be used. Serum is most commonly used for diagnostic purposes. Animal sera are used in humans for therapeutic purposes.

Plasma can be considered as the crude product of precipitation of blood whereas serum is the refined plasma minus the fibrinogen and the other clotting factors.

  • Retired 3rd Infantry Grunt

    More commonly, vacutainer tubes used to collect serum for clinical chemistry analysis are green (heparin) SST (Serum Separator Tubes) which are centrifuged prior to analysis. The gel at the bottom of the SST tube changes viscosity during centrifugation and permanently traps all the cells, RBC’s, WBC’s and platelets.