What's the Difference Between Serum and Plasma?

For some scientists and medical students, the difference between serum and plasma is just nomenclature and colour. On more than once occasion we’ve had to ask the difference between Serum and Plasma, only to hear, “either one” or “aren’t they the same thing?” Let us clear up the confusion by consistently elaborate on the various differences and level of application in the medical laboratory or health field.

What's the Difference Between Serum and Plasma?
What's the Difference Between Serum and Plasma?

What is Blood?

Blood is a body fluid in humans and other animals involves in the transportation and delivery of necessary substances such as nutrients and oxygen to the cells and metabolic waste products away from those same cells.

It is composed of blood cells suspended in blood plasma. Plasma, constitutes 55% of blood fluid that is 92% by volume of mostly water and contains proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), and blood cells themselves. The blood cells are mainly red blood cells (erythrocytes), white blood cells (leukocytes) and platelets (thrombocytes). By volume, the red blood cells constitute about 45% of whole blood (plasma and cells), the plasma about 54.3%, and white cells about 0.7%.

What is Blood Plasma

  • It is a yellowish liquid component of whole blood that carries cells and proteins throughout the body (Transportation).
  • It normally holds the various blood cells in whole blood in suspension. It makes up about 55% of the body's total blood volume. 
  • Blood plasma is an intravascular fluid part of extracellular fluid (all body fluid outside cells) mostly made up water (up to 95% by volume) that contains dissolved proteins (globulins ,serum albumins and fibrinogen), glucose, clotting factors,  hormones, electrolytes (Na+, Ca2+, Mg2+, HCO3, Cl, etc.), oxygen and carbon dioxide (plasma being the main medium for excretory product transportation).
  • It plays a vital role in an intravascular osmotic effect that keeps electrolyte concentration balanced and protects the body from infection and other blood disorders.

How is Blood Plasma Obtain?

It is obtain from blood by spinning a tube of fresh blood containing an anticoagulant in a centrifuge. This process causes the blood cells to fall to the bottom of the tube. The yellowish supernatant is the Plasma.

What is Blood Serum

The Component in blood the does not contain neither a blood cell (WBC and RBC), nor a clotting factor is known as Serum

  • Serum does not contain fibrinogens. It includes all proteins not used in blood clotting and all the electrolytes, antibodies, antigens, hormones, and any exogenous substances (e.g., drugs and microorganisms) found in plasma

The study of serum and it’s contain is known as Serology.

How is Blood Serum Obtain?

 Blood is centrifuged to remove cellular components. Coagulated blood yields serum free from fibrinogen, although some clotting factors are present therefore Blood serum is blood plasma without clotting factor (fibrinogen).

From the above explanation, we can point out the main difference between Blood Plasma and Blood Serum which is the presence of clotting factor (Fibrinogen).Therefore, what are the importance of clotting factors

The Importance of Clotting (Fibrinogen)

The clotting process activates a cascade of proteolytic enzymes (proteases).This results in the conversion of Prothrombin to Thrombin, which is an enzyme that converts Fibrinogen into Fibrin in order for blood to clot. Platelets are activated in the process and release a set of compounds, which naturally alters proteins in the serum. In coagulated or clotted blood, Fibrinogen has been converted to Fibrin producing Serum free of Fibrinogen. Meanwhile, when blood is collected in anticoagulant tube and spun, the resultant fluid obtained is Plasma.

Factors for Comparison




It is the watery fluid portion of the blood through which several blood cells are diluted.


The fluid or undiluted part of the blood that remains after the blood has clotted

How it’s obtained

It is obtained after Spinning blood in an anticoagulant tube

From centrifuging clotted blood


Light Yellow clear

Light Yellow clear


Approximately 1.025 g/ml, or 1025 kg/m3.

density of 1.024 g/ml.


It makes up 55% of the total blood

Has a lesser volume as compare to Plasma


Needed to obtain Plasma

No anticoagulant is needed





·         All proteins

·         Clotting factors

·         Metabolites

·         Electrolytes

·         Blood cells

·         All proteins

·         Clotting factors except Fibrinogen

·         Metabolites

·         Electrolytes

·         Antibodies

Water content     

About 92- 95% water

90% water      


Can be Frozen and store for Almost a year

At 2-6 °C for several days.

Cellular structure

Cells are not attached together but suspended in plasma.

Cells are usually attached together by clot formation.


Plasma is easily separated

Serum is hard to separate


Mostly used in problems relates to blood-clotting.

The most preferred blood part used mostly in checking blood groups. 


It helps in regulation of body temperature and maintenance of blood pressure.

Used for various diagnostic tests such as determining the levels of hCG, cholesterol, proteins, sugar, etc., in the blood.


Supports the transportation of substances such as glucose and other nutrients through the blood

The animal serum is used as anti-toxins, anti-venom and for vaccinations.


To conclude, Blood is one of the most important tissue of the body that helps in the transportation of vital substances such as nutrients, hormones, gases, vitamins, etc.

Blood contains Plasma and Serum which can be differentiate base on the presence or absence of Fibrinogen respectively based on the method of separation (presence or absence of anticoagulant).

Scientists and healthcare professional should always take their time to understand various differences of these blood product before performing medical procedures in order to encourage accuracy and reliability of laboratory results or services.



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