For some scientists, the difference between serum and plasma is just nomenclature. On more than once occasion we’ve had to ask customers, “Do you mean serum or do you mean plasma?” only to hear, “either one” or “aren’t they the same thing?” Let us clear up the confusion.
Serum vs. Plasma: What’s the Difference?
Serum and plasma both come from the liquid portion of the blood that remains once the cells are removed, but that’s where the similarities end.
Serum is the liquid that remains after the blood has clotted.
Plasma is the liquid that remains when clotting is prevented with the addition of an anticoagulant.
This is not an insignificant difference.
The Importance of Clotting
The clotting process activates a cascade of proteases, which results in the conversion of prothrombin to thrombin, an enzyme that converts fibrinogen into fibrin to clot blood. Platelets are activated in the process and release a set of compounds, which naturally alters proteins in the serum.
To collect plasma, an anticoagulant is added to the centrifuged whole blood, which can impact testing. EDTA is the most commonly used anticoagulant in clinical diagnostic labs. EDTA chelates the calcium needed for clotting, but can also inhibit other enzymes. There are many other anticoagulants in use such as citrate, heparin, and fluoride, each with appropriate uses.
When to Use Serum, Plasma or Both
Whether you’re developing a diagnostic test, supplementing a cell culture, or running a research assay, we recommend using both serum and plasma so you can observe how different sample types behave. If you use only one, you could be misled by false results.
For example, clotting factors in serum or the platelets and cellular elements that contaminate plasma could interfere with or alter your results. If your results are the same for serum and plasma, then you have more flexibility in sample usage.