Difference between Serum and Plasma

The human blood consists of different components. Two of them is plasma and serum. These two terms are used frequently but play different roles in the body. Serum and plasma are the liquid part of the blood. These components remain when the cells’ components are taken out.

Serum is the liquid component of the blood that remains once the blood has clotted. On the other hand, plasma is the liquid part that remains when clotting does not take place and the anticoagulant is added. ^{(1, 2, and 3)}

Image 1: Serum is the fluid component of the blood.
Picture Source: medimoon.com

Image 2: A test tube labeling the plasma component of the blood.
Picture Source: givingblood.org

Why clotting is important?

The blood clotting process converts prothrombin to thrombin; an enzyme that is responsible for converting fibrinogen to fibrin. During such process, platelets are activated and release a compound that alters the protein in the serum.

Plasma is collected by adding anticoagulant to the centrifuged whole blood. One of the commonly used coagulants in the clinical diagnostic laboratory is EDTA. Other anticoagulants include heparin, citrate, and fluoride. ^{(2, 3)}

Image 3: Two test tubes with plasma and serum blood components.
Picture Source: actforlibraries.org

 

Plasma and serum: Definition

Serum

A blood component similar to plasma but minus the blood’s clotting factors. Serum is the resources for antigens, proteins, antibodies, electrolytes, and hormones.

It plays an important role in disease diagnosis, especially medical conditions that have something to do with blood pressure, cholesterol, and blood sugar. It is also used in blood typing procedure. ^{(3, 4)}

Plasma

A blood medium wherein the red blood cells, white blood cells, and other blood components are suspended. Majority of the total blood volume is covered by plasma. It has a clotting agent called fibrinogen. The clotting factor plays an important role during injury as it helps prevent excessive flow of blood in the injury site. ^{(3, 4)}

Plasma and serum compositions

Serum

Serum is the liquid part that does not contain the clotting factor. Its density is 1.024 g/ml. Its components include:

• Antibodies
• Hormones
• Antigens
• Electrolytes
• Water
• Proteins
• Antibodies ⁽⁴⁾

Plasma

It is the yellow part of the liquid component of blood (55% of the total blood volume) and a density of about 1.025 g/ml, or 1025 kg/m3. Its components include:

• Serum
• Clotting factor
• Albumin
• Water
• Globulin ⁽⁵⁾

Plasma and Serum Functions

Serum

• It is used as antitoxins and anti-venom (animal serum) for vaccination.
• It is used to diagnose medical conditions that have something to do with blood glucose level, proteins, cholesterol, and the likes.
• Blood serum is used in blood typing. ^{(4, 5, and 6)}

Plasma

• It supports the transport of materials such as glucose and other essential nutrients through the blood.
• It regulates body temperature.
• It helps maintain healthy blood pressure.
• It is mostly used in conditions that have something to do with blood clotting. ^{(6, 7)}

Image 4: Centrifugation and aliquoting blood.
Picture Source: i.ytimg.com

Image 5: Fresh blood plasma for transfusion.
Picture Source: wikimedia.org

Isolation procedure

Serology is the study and analysis of serum for diagnostic purpose.

 

Serum

1. Collect whole blood in a test tube. Make sure that the test tube is covered.
2. Let the blood clot by leaving it undisturbed at room temperature. It would take around 15 minutes to 30 minutes.
3. Remove the clot by a centrifuge at 1,000–2,000 x g for about 10 minutes in a refrigerated centrifuge.
4. Serum is the resulting supernatant.
5. Immediately transfer the liquid component of the blood into a clean tube using a Pasteur pipette. The serum should be immediately analyzed.
6. If the serum is stored for future use, it should be apportioned into 0.5 ml aliquots and stored at -20°C or lower.
7. Avoid freeze-thaw cycle because it can alter the components of blood serum. ^{(5, 6, 7, and 8)}

Additional information:

It was Karl Landsteiner who discovered blood serum by studying different types of blood. He noticed an agglutination effect when two different blood types were mixed.

Plasma

The process of isolating plasma from the blood through centrifugation is called plasmapheresis.

1. Collect whole blood into an anticoagulant-treated tube.
2. Through centrifugation for 10 minutes at 1,000–2,000 x g using a refrigerated centrifuge plasma is removed from the cells.
3. The resulting supernatant is plasma.
4. Right after centrifugation, transfer plasma immediately into a clean polypropylene tube using a Pasteur pipette.
5. The right temperature should be maintained while handling the sample (2–8°C).
6. The plasma should be analyzed immediately.
7. If not analyzed right away, plasma should be apportioned into aliquots (0.5ml) and transported at –20°C or lower.
8. Make sure to avoid freeze-thaw cycles as it may invalidate certain laboratory procedures. ^{(3, 6, 8, and 9)}

Additional information:

Gordon R. Ward discovered the importance of blood plasma for transfusion in 1918.

Differences between plasma and serum refer to the table below.

Subject of comparison	Serum	Plasma
Definition	An extracellular fluid part of the blood that remains after completing the coagulation process.	It is the straw to a yellowish colored fluid component of the blood wherein all the blood cell components of the blood are suspended.
Components	All proteins Metabolites Electrolytes	All proteins Clotting factors
Discovery	It was discovered by Karl Landsteiner in 1901.	Its use was discovered by Gordon R. Ward in 1918.
Process of extraction	Blood serum is extracted through the process of centrifugation. This process results in coagulation of blood components at the bottom and the serum stays on top.	Plasma is extracted through the process of centrifugation wherein an anticoagulant is added to the blood sample. (3, 6, and 9)
Volume	A small percentage of the total blood volume.	About 55% of the total blood volume.
Density	1.024g/ml	1.025g/ml
Cellular structure	Cells stick together in a mesh-like framework.	Cells are present in a suspended form.
Water content	90% water	About 95% water
Use of anticoagulant	Not necessary	Necessary
Functions	It is used as antitoxins and anti-venom (animal serum) for vaccination. It is used to diagnose medical conditions that have something to do with blood glucose level, proteins, cholesterol, and the likes. Blood serum is used in blood typing.	It supports the transport of materials such as glucose and other essential nutrients through the blood. It regulates body temperature. It helps maintain healthy blood pressure. It is mostly used in conditions that have something to do with blood clotting. (2, 9, and 10)

Plasma and serum are essential blood components. They may have a lot of differences but they definitely have their own set of functions. People use plasma and serum interchangeably but they are different entities.

They differ in components, characteristics, and functions. Those who work in the medical field should be cautious to not interchange the two, especially during a blood transfusion or when performing a particular laboratory procedure.

References

1. https://medimoon.com/2012/07/difference-between-plasma-and-serum/
2. https://astartebio.com/blog/ask-scientist-whats-difference-serum-plasma/
3. http://microbiologynotes.com/differences-between-serum-and-plasma/
4. https://www.westlab.com.au/blog/2018/07/27/what-is-the-difference-between-plasma-and-serum
5. https://microbiologyinfo.com/difference-between-serum-and-plasma/
6. https://patch.com/washington/seattle/serum-vs-plasma-whats-difference
7. https://biodifferences.com/difference-between-plasma-and-serum.html
8. https://www.bioexplorer.net/differences-between-serum-and-plasma.html/
9. https://www.sciencedirect.com/science/article/pii/S000326701830374X
10. https://www.thermofisher.com/ph/en/home/references/protocols/cell-and-tissue-analysis/elisa-protocol/elisa-sample-preparation-protocols/plasma-and-serum-preparation.html