For a significant percentage of individuals, plasma and serum mean the same and are often used interchangeably. However, the similarities between plasma and serum are mainly limited to the source – the liquid blood after removal of cells. Beyond that there are differences that are notable and make both plasma and serum different. Here is a look at the differences between the two; which will help you understand the role of both and the effects of clotting. There are distinct advantages of each over the other, and these advantages depend on the use and the policy of hospitals that draw the samples. As we highlight the difference between plasma and serum we will also showcase the benefits of each and the advantages in specific requirements. Let’s begin by understanding each better.

What is plasma and what are the functions of plasma?

Before we look at the difference between plasma and serum lets take a good look at plasma and the functions of plasma. Plasma is effectively more than half of the blood in the body and is nothing but the liquid portion of blood. White blood cells, platelets and red blood cells comprise the remaining portion of blood and are actually suspensions in plasma. By virtue of being the liquid portion of blood, water comprises the bulk of plasma, accounting for 92%, while minerals hormones, vitamins and sugar constitute 1%, and the remaining 7% taken up by other essential proteins including albumin and gamma globulin. Among the various functions, the four important functions of Plasma include – (1) maintenance of pH balance in the body which is essential for the cells to function smoothly, (2) movement of electrolytes to the muscles, (3) maintenance of blood volume and pressure and (4) supply of essential proteins that are vital for immunity and for blood clotting properties.

What is serum and what are the functions of serum?

Now that we have looked at plasma, it is time to look at serum to understand the difference between plasma and serum better. Serum is the fluid component of blood and the first difference between serum and plasma is the clotting factor. Serum does not have any function in clotting, while plasma has clotting properties. Serum has multiple uses, including its use for diagnostics to determine various health parameters of the subject patient. Additionally serum is also used for research purpose during clinical trials to determine the candidates ability to respond to clinical trials of medications. The process of obtaining serum is different from the process used for plasma.

Differences between serum and plasma

The primary difference between plasma and serum is given below :

#1 Composition

Serum is the liquid portion of blood with blood clotting properties, while Plasma is the fluid part, with no role in clotting. Plasma is the substance in which other constituents of blood are suspended, while serum contains antigens, hormones, and electrolytes. Water accounts for 92 percent of plasma, while comprising 90% of serum. Fibrinogen is absent in serum and present in plasma.

In serum cells are attached to each other through clotting, while in plasma, cells are suspended in plasma and not attached to each other.

#2 Amount of plasma and serum in blood

Plasma makes up more than half (55% to be precise) of the total volume of blood, while the quantity of serum is considerably lower. The density of plasma and serum are more or less similar with serum having a density of 1.024 g/ml, while plasma has a density of 1.025 g/ml.

#3 Method of separation from blood

To separate plasma from blood anti-coagulation process is required, while serum separation from blood does not involve the use of anti-coagulants. It takes a lot of time to separate serum from blood, while separating plasma from blood takes relatively lesser time to complete. Serum is obtained through spinning after clotting process of blood, while it is the exact opposite in plasma – obtained through spinning prior to the clotting of blood.

#4 Storing blood components

Plasma can be frozen and stored for upto a year easily, while serum can only be stored for days when stored in ideal temperature settings.

#5 Main uses

Serum is primarily used in diagnostics – for checking blood group, and for mapping cholesterol levels, proteins, sugar and hCG in the blood. The serum of animals has critical applications and is used for vaccinations, as anti-venom and anti-toxins.

Plasma is typically used for boosting the blood cell count of patients by virtue of being the medium for transportation of dissolved nutrients. It is used for maintaining blood pressure, volume of blood and body temperature of patients.

Among the differences, it is important to note one difference between plasma and serum – plasma is actually serum with clotting factor. To put it differently, while serum is the part of blood without the clotting factor, plasma is serum with the clotting factor. This essentially sums up the differences between plasma and serum.

What is the role of clotting and why is it important?

As we look at the difference between plasma and serum, it is clear that one of the most important difference is the clotting factor. Let us therefore look closer into this and understand the role of clotting and why clotting is important.

Clotting is essential to stop individuals from loss of blood. Coagulation is activated when the body detects bleeding in a particular spot. This is achieved through two different pathways – intrinsic and extrinsic. The intrinsic is the initiation stage and the extrinsic is the amplification stage. Both these stages combine to form clotting at the location. The conversion of prothrombin to thrombin results in the formation of blood clots when fibrinogen changes into fibrin. During this process platelets are activated and this brings about a change in the serum protein.

Is it important to rely on plasma and serum samples during diagnostics or will one suffice?

The difference between plasma and serum indicates that both serum and plasma differ, despite having an overlap of source and functions. At times, when diagnostic tests are conducted, serum as well as plasma is used, in order to understand how the different samples behave. This helps to avoid false results that may be possible in one sample. Using both plasma and serum for diagnostics helps eliminate errors as each confirms the results of the other. For instance, clotting factors may have an impact on the results when plasma samples alone are used for diagnostics. However, if diagnostics also relies on serum, the possibility of errors in results are eliminated as comparison helps determine the impact or absence of any impact of clotting on the results.

FAQs that clarify certain practices and preferences in the use of plasma and serum

As can be seen from the difference between plasma and serum, both are used for specific purposes, yet for the purpose of certain diagnostics, the general practice is to use both samples. Here are FAQs that clarify certain practices and preferences in the use of plasma and serum.

Why is serum preferred for chemistry testing?

Typically serum samples are used during chemistry testing. The reason behind this preference is the chemistry reference intervals, which are on the basis of serum. The levels of enzymes and proteins in serum are more than plasma and this makes it a better choice for chemistry testing. For instance, levels of LDH (lactate dehydrogenase) potassium and phosphate are recorded to be higher and this makes serum a good choice for chemistry testing. The reason behind the higher levels of enzymes and proteins is attributed to their release during clotting. Consequently, serum is a better choice for chemistry testing.

When is plasma administered to patients?

It is essential to understand when plasma is administered to patients as this will give a better understanding of the difference between plasma and serum. Plasma is typically administered to patients suffering from burn, shock and trauma. Additionally plasma is also given to patients with serious liver conditions and clotting deficiencies. The purpose of administering plasma to patients is to increase the volume of blood which helps to fight shock. Another critical function is the assistance in blood clotting, which helps handle serious conditions of patients with clotting deficiencies. Plasma is an important ingredient in formulations of pharma companies in treatment options for handling immune and clotting deficiencies.

Processes involved in serum preparation

Serum preparation involves the collection of whole blood in a test tube (covered). Red tubes are typically used and are known as blood handling tubes. The blood is then allowed to clot at room temperature, which typically takes around 30 minutes. Following this, the clot is removed through centrifuging in a refrigerated centrifuge. This process usually takes around ten minutes at around 2000 x g. After centrifuging, the liquid is immediately transferred to a PP tube through a pipette. It is important to ensure that the handling process exposes the liquid samples to 2-8 deg C. The serum can then be used for analysis. In the event that the serum is not used for immediate analysis, it is then stored at -20deg C.

Processes involved in plasma preparation

Serum preparation involves the collection of whole blood in tubes that are anti-coagulant treated. These tubes are typically known as EDTA treated tubes. The cells are then removed from plasma through centrifugation in a refrigerated centrifuge for a duration of ten minutes at 2000 x g. Here it is important to note that centrifugation for a duration of fifteen minutes at 2000 x g can reduce the platelets. After the process of centrifugation, the liquid needs to be immediately transferred to clean PP tubes through a pipette. Here again, during the process of handling, the samples need to be maintained at 2 – 8 deg C. The samples can then be used for analysis. However, if the samples are not intended to be used for analysis immediately, storage at -20 deg C or lower is necessary.

How much of whole blood is required for desired plasma/serum volume

For 5 mL of plasma that is required, 12 mL of whole blood needs to be drawn. Similarly, for 5 mL of serum that is required, 12 mL of whole blood needs to be drawn. These are standard specimen handling practices used while drawing blood samples for plasma and serum.


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