What is the difference between serum and plasma?

Blood test is a great rapid test for COVID-19 detection. The different specimens will have big different final results while doing covid-19 antibody test. All rapid test will require to detect based on whole blood, plasma or serum. So, what’s the difference between serum and plasma? Serum VS Plasma as below.

What does blood consist of?

Blood consists of plasma and blood cells.

(1) Plasma

Plasma is equivalent to the intercellular substance of connective tissue. Serum is a light yellow translucent liquid. In addition to a large amount of water, plasma contains inorganic salts, fibrinogen, albumin, globulin, enzymes, hormones, and various nutrients, etc. These substances do not have a certain shape, but have important physiological functions.

1L of plasma contains 900～910g water (90%～91%), 65～85g protein (6.5%～8.5%) and 20g low molecular substance (2%). There are many electrolytes and small molecular organic compounds in low molecular substances, such as metabolites and some other hormones. The electrolyte content in plasma is basically the same as that in tissue fluid.

(2) Blood cells

During the life of the body, blood cells are constantly metabolizing. The average life span of red blood cells is about 120 days, and the life span of granular white blood cells and platelets generally does not exceed 10 days. The life span of lymphocytes varies from a few hours to several years.

Blood cells and platelets are produced from hematopoietic organs. Red blood cells, granular white blood cells and platelets are produced by red bone marrow, while agranulocytes are produced by lymph nodes and spleen.

There are three types of blood cells: red blood cells, white blood cells, and platelets.

An adult has about 5 liters of blood. By volume, blood cells account for about 45% of blood. Each liter of blood has:

5x10¹² Red blood cells (about 45% of blood volume): In mammals, mature red blood cells have no nucleus and organelles. They have heme to transport oxygen. The glycoprotein on the red blood cell determines the blood type. The proportion of red blood cells in the blood is called hematocrit. The total surface area of ​​all red blood cells in the human body is approximately 2000 times the area of the skin outside the body.

9x10¹¹ White blood cells (about 1.0% of blood volume): They are part of the immune system, responsible for destroying and removing old or abnormal cells and cell debris, and attacking pathogens and foreign objects.

3x10¹¹ Platelets (approximately less than 1% of the blood volume): They are responsible for blood clotting, turning fibrinogen into fibrin. Fibrin forms a network to gather red blood cells to form a thrombus, which prevents more blood loss and helps prevent bacteria from entering the body.

What is plasma?

Plasma definition: Plasma refers to the liquid part of the whole blood after separation. It is based on a solution of crystalline substances, including water and a variety of electrolytes, as well as small molecules of organic matter and gases dissolved in it.

Classification of plasma

1. Fresh plasma: Contains normal amounts of all coagulation factors. It is suitable for patients with coagulation factor deficiency.
2. Preserved plasma: Suitable for patients with low blood volume and low plasma protein.
3. Frozen plasma: Ordinary frozen plasma is stored at low temperature ~ 30℃ and is valid for 1 year. Melt in 37℃ warm water before application.
4. Fresh frozen plasma: In the United States, it refers to the fluid portion of one unit of whole blood that has been centrifuged, separated, and frozen solid at −18 °C (0 °F) or colder within eighthours of collection from whole blood donation or was otherwise collected via apheresis device.
5. Dried plasma: appropriate amount of 0.9% sodium chloride solution or 0.1% sodium citrate solution can be added for dissolution.

Appearance

Plasma is equivalent to the intercellular stroma of connective tissue. Plasma has a pale yellowcolor because it contains bilirubin. Water makes up 90 to 92 percent of the chemical composition of the plasma, with the other 10 percent in the form of solutes in proteins, nutrients, hormones, cholesterol, and other important substances.

 Function

Carry blood cells, transport substances needed to maintain the body and producing waste, etc.

How is plasma donated?

 Plasma donation is one of the methods of component blood donation. The technology of plasma donation is to extract the human blood from the body, separate it in the automatic machine, and return red blood cells to the donor. Only the plasma part is collected. The whole process uses disposable consumables and is completed in completely enclosed environment. Plasma donation is one of best way to treat the novel coronavirus for it includes antibody of SARS-CoV-2. How to donate plasma? Should consult the local authority department.  

How do you increase plasma in your body?

1. Drink vitamin or iron supplements: Sometimes vitamin C helps the body absorb iron. Low levels of vitamin or iron in the body can cause certain types of anemia.
2. Change your diet: It is recommended to eat more red meat, especially beef or liver, and chicken, pork, fish and shellfish are also rich in iron and can be used as a salubrious diet to treat anemia.
3. Drugs: With too little blood in your body, your doctor may help prescribe drugs to help your body produce more red blood cells.

What is serum?

Serum definition: Blood serum refers to the gelatinous fluid in plasma after fibrinogen is removed.

Components

It is mainly composed of water and various chemical components, such as albumin, α1、α2、β、γ-globulin, triglyceride, total cholesterol, alanine aminotransferase and so on. Serum contains a variety of plasma proteins, peptides, fats, carbohydrates, growth factors, hormones, inorganic substances, and so on. These substances promote cell growth or inhibit growth activity so as to achieve physiological balance.

What does a serum do?

1. Provide essential nutrients: amino acids, vitamins, inorganic substances, lipids, nucleic acid derivatives, etc.
2. Provides hormones and various growth factors
3. Provide binding proteins: Binding proteins act as carriers of important low molecular weight substances
4. Provides contact - promoting and extension factors to protect cells from mechanical damage
5. It has some protective effect on cultured cells.

What is the difference between serum and plasma?

Serum vs Plasma

1. Definition: The answer is given above.
2. Relationship: As defined above, serum is contained in plasma.
3. Color:
   1. The plasma is the remaining part of the whole blood after the separation of bleeding cells, which is pale yellow.
   2. Serum refers to the clear liquid precipitated on the surface of the blood clot after the coagulation of plasma, which is light yellow and transparent.
4. Density: Plasma contains a variety of coagulation factors, so its density is higher than the serum.
5. Composition: The biggest difference is the absence of fibrinogen in the serum.
6. Coagulation: The addition of calcium ions to plasma causes it to solidify, while it can’t do it to serum.
7. Clotting factors: Plasma contains clotting agents. While serum is a watery fluid in the blood without clotting factors.
8. Water content: Plasma contains 92-95% water. While 90% of the serum is water.
9. Components: Plasma contains clotting factors and water. Serum contains albumin and globulin and other proteins.
10. rrangement: The cells are not attached and are suspended in plasma. While for serum, cells usually stick together through the formation of blood clots.
11. Separation: Plasma is acquired from the spinning before clotting.
    While serum is obtained from the spinning after clotting.
12. Function: Plasma is mainly applied to the detection of coagulation, and serum is mainly used for the detection of blood biochemistry, immunity and other aspects.
13. Anticoagulants: Anticoagulants are needed to obtain plasma. While anticoagulants are not required for the separation of serum.
14. Feasibility of separation: Plasma separation is relatively easier and cheaper.
15. The amount of blood: Plasma accounts for 55% of the total blood. Serum has a smaller portion.
16. Storage: Frozen plasma can be stored for up to one year. Serum can be stored at 2-6 degrees (Celsius) for just several days.
17. Discoloration: Plasma shows an inclination to discolor when standing, and serum does not.
18. Significance: The function of plasma is the excretion of metabolites and transport of substances in the blood. It also helps maintain blood pressure and regulate body temperature. While serum is a major source of electrolytes.

FAQ

1. Why serum is used instead of plasma?

Situations in which serum rather than plasma is commonly used:

• Protein Electrophoresis
• Lactic acid determination
• Determination of amylase
• Rapid HIV test
• Biochemical project

2. Are antibodies is plasma or serum?  

Antibodies exist in serum, lymph, mucosal secretions and tissues, but with the highest content in serum. And antibodies are often obtained by the separation of the serum, so antibodies are also called anti-serum.

3. What is plasma membrane function?

There is no relevance between plasma membrane and plasma.
Plasma membrane was used to be called “cell membrane”, which is a very thin membrane that surrounds the cell surface and is mainly composed of membrane lipids and membrane proteins.

The basic role of the plasma membrane is to maintain the relative stability of the intracellular microenvironment and to participate in the material exchange with the external environment. In addition, it plays a crucial part in the survival, growth, division and differentiation of cells.

Conclusion

Serum vs plasma: The difference between them is clearly shown in above information, which can help design IVD product while doing lateral flow assay development in in-vitro diagnostics.

References

• Yentis, Steven M.; Hirsch, Nicholas P.; Ip, James (2013). Anaesthesia and Intensive Care A-Z: An Encyclopedia of Principles and Practice. Elsevier Health Sciences. p. 147. ISBN 9780702053757. Archived from the original on 2017-09-23.
• Dennis O'Neil (1999). "Blood Components". Palomar College. Archived from the original on June 5, 2013.
• Tuskegee University (May 29, 2013). "Chapter 9 Blood". tuskegee.edu. Archived from the original on December 28, 2013.
• Wikipedia: Serum (blood)
• Differences between Human Plasma and Serum Metabolite Profiles