What Is the Difference Between Serum and Plasma?
Plasma and serum are two liquid components of blood and the difference between serum and plasma is one of the most frequently tested topics of NEET in the chapter Body Fluids and Circulation (Class 11 Biology). The simple answer is that the serum is the liquid part of blood without the blood-clotting elements, whereas plasma is the liquid part of blood with the blood-clotting factors. To put it simply, Serum = Plasma – Clotting Factors.
The fluid part of blood is known as plasma. Both are a pale-yellow colour. It has everything: proteins, hormones, nutrients, waste and indeed, the clotting factors such as fibrinogen. However, the difference between serum and plasma is the presence or absence of fibrinogen, which alters their acquisition, contents and applications.
In this blog, we cover the definitions of plasma and serum, a detailed NCERT-based comparison table, their functions for boards and NEET exam, and practice MCQs in the exact format asked in NEET.
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What Is Blood Plasma? Definition and Composition
Blood plasma is the liquid, non-cellular part of blood. It makes up about 55% of the total blood volume and looks pale yellow or straw-coloured. When you remove all the blood cells, RBCs, WBCs, and platelets using an anticoagulant, what is left behind is plasma.
It is obtained by adding an anticoagulant like EDTA, heparin, or sodium citrate to blood and then centrifuging the sample. The cells settle down; plasma floats to the top.
Composition of plasma:
- Water: ~90-92% of plasma volume
- Proteins: albumin (most abundant), globulins, fibrinogen
- Inorganic salts: sodium, potassium, calcium, bicarbonates, phosphates
- Nutrients: glucose, amino acids, fatty acids, vitamins
- Dissolved gases: oxygen and carbon dioxide
- Waste products: urea, uric acid, creatinine, ammonia
- Hormones and enzymes
An important thing to remember: Plasma contains fibrinogen that serves as a clotting protein. These are the main factors that separate plasma from serum.
What Is Serum? Definition and Key Components
Serum is the clear fluid that remains after blood has been allowed to clot naturally, and the clot is removed by centrifugation. No anticoagulant is used. Blood is simply left to clot for 30–60 minutes, then spun. The transparent supernatant is serum.
Serum is essentially plasma without fibrinogen and other clotting factors. Everything else – antibodies, hormones, albumin, electrolytes, globulins is still present.
Students should know: In serum, the concentration of antibodies is higher than in plasma, because it does not contain clotting proteins. This is why serum is preferred for serological and diagnostic tests.
Serum vs Plasma: Core Difference at a Glance
Quick Answer for NEET Revision:
- Plasma: It is the liquid part of the blood that contains clotting factors due to the presence of fibrinogen
- Serum: It is the liquid part of the blood that lacks clotting factors, which means fibrinogen is absent.
- Plasma is obtained using anticoagulants; Serum is obtained after blood clots naturally
- Serum is obtained by letting blood clot naturally + centrifugation
- Only plasma contains: fibrinogen, prothrombin, and other coagulation factors
- Both Plasma and Serum contain hormones, electrolytes, antibodies and albumin.
Difference Between Serum and Plasma: Detailed NCERT-Based Comparison Table
The table given below contains all the key differences between plasma and serum that are important for NEET 2027 and the Class 11 boards. Read them nicely, as the NEET test the applications of these differences and not just (just in case definition) theory.
| Basis | Plasma | Serum |
| Definition | The liquid part of blood that contains clotting factors | Plasma without clotting factors; obtained after blood clots |
| Clotting Factors | Present (fibrinogen, prothrombin, etc.) | Absent |
| Composition | Water (~90-92%), proteins, electrolytes, hormones, nutrients, dissolved gases, and waste products. | Water, proteins (albumin, globulins, but no fibrinogen), electrolytes, hormones, antibodies, and enzymes. Clotting proteins are absent. |
| Components / Proteins | It contains all the proteins of plasma, albumin, globulins, and fibrinogen (clotting protein). It also contains prothrombin and other coagulation factors. | It contains albumin and globulins. Other clotting factors and fibrinogen are absent. |
| Cell Arrangement | Plasma suspends all formed elements of blood – RBCs, WBCs, and platelets. | Serum contains no blood cells and no platelets. It is a cell-free fluid obtained after the clot is removed. |
| Fibrinogen | Present | Absent |
| Method of Separation | Blood + anticoagulant – centrifugation | Blood allowed to clot – centrifugation |
| Colour / Appearance | Pale yellow/straw-coloured, due to the presence of lipoproteins and clotting proteins | Clear to light yellow, because it lacks the clotting proteins that add slight turbidity. |
| Protein Content | Higher (contains clotting proteins) | Slightly lower (no clotting proteins) |
| Water Content | ~90-92%, Slightly higher water content compared to serum. | Slightly less than plasma |
| Antibodies | Present | Present (more concentrated) |
| Volume in Blood | ~55% of total blood volume. It is the largest single component of blood. | Less than plasma volume, because clotting factors and fibrin are removed from it. |
| Use / Application | Blood transfusions, plasma therapy | Diagnostic tests, antivenom, vaccines |
| Anticoagulant Used? | Yes (EDTA, heparin, sodium citrate) is required to prevent clotting before separation. | No anticoagulant used |
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Functions of Blood Plasma: Important for NEET & Class 11 Boards
Plasma is often called the “transport highway” of the body. It does far more than just carry blood cells around. Given below are the functions of blood plasma that are important to know from the NEET 2027 perspective:
- Nutrient transport: Carries glucose, amino acids, fatty acids, and vitamins from the intestine and liver to all tissues.
- Waste removal: Transports urea, uric acid, and creatinine from body cells to the kidneys for excretion.
- Blood clotting: Fibrinogen in plasma converts to fibrin at an injury site, forming a clot and stopping blood loss.
- Osmotic pressure: Albumin maintains the osmotic balance between blood and tissues. Low albumin causes fluid to leak into tissues, resulting in oedema, a concept NEET applies in MCQs.
- Blood pressure and volume: The presence of plasma affects the pressure of blood. In case of a decrease in plasma (e.g., burns), a drop in pressure is witnessed.
- Immune response: Globulins (immunoglobulins) act as antibodies and fight infections.
- pH regulation: Plasma proteins and bicarbonate ions buffer blood pH, keeping it at ~7.4.
- Hormone transport: Hormones like thyroxine travel bound to plasma proteins to their target organs. And water-soluble hormones (like insulin or epinephrine) travel in plasma freely.
Note for students: The protein albumin is synthesised in the liver and is the most abundant plasma protein. It is responsible for maintaining colloidal osmotic pressure. A fall in albumin (due to liver disease or malnutrition) is one of the first signs of serious illness. This is an applied NEET concept.
Functions of Serum: What You Need to Know for NEET Biology
Serum does not contain clotting factors, but it is useful in both labs and clinically. Given below are some functions of serum that are important for NEET.
- Diagnostic testing: Serum is used for liver function tests (LFT), kidney function tests (KFT), lipid profiles, and most serological tests. It is the standard sample for blood reports.
- Blood group determination: Serum from a person with a known blood type contains specific antibodies (agglutinins). It is used to identify another person’s blood group through agglutination, a direct NEET application.
- Immunity: Serum carries immunoglobulins that neutralise pathogens. This is the basis of passive immunity.
- Antivenom and antitoxins: Horse serum containing antibodies against snake venom or bacterial toxins is used as a therapeutic in humans.
- Cell culture: Foetal bovine serum (FBS) is widely used as a growth supplement in cell and tissue culture connects to the Biotechnology chapter in Class 12.
- Hormone transport: Like plasma serum also contains hormones and electrolytes that help to target the organs.
Remember: Serum does not help with blood clotting due to a lack of fibrinogen. Serum is mostly used for diagnostic and immunological applications. Remember this difference, NEET options often trick students by attaching rules of clotting to serum.
Check Out: NEET 2026 Sample Papers with Solutions (Latest Exam Pattern)
NEET Practice Questions: Serum and Plasma (Exam-Pattern MCQs for NEET 2027)
Practice these questions the way NEET asks them. The answer logic is explained after each question.
Q1. Which of the following is present in plasma but absent in serum?
- (a) Albumin
- (b) Fibrinogen
- (c) Globulins
- (d) Antibodies
Answer: (b) Fibrinogen, Serum is plasma minus clotting factors. Fibrinogen is a clotting factor and is absent in serum.
Q2. A blood sample is collected in a tube without an anticoagulant and left at room temperature. After centrifugation, the fluid obtained at the top is:
- (a) Plasma
- (b) Serum
- (c) Lymph
- (d) Whole blood
Answer: (b) Serum, because there is no anticoagulant, the blood naturally clots at room temperature. During this process, fibrinogen converts to fibrin, converting blood cells into a solid clot. Centrifugation spins this heavy clot to the bottom, leaving serum at the top.
Q3. Blood plasma is obtained by:
- (a) Allowing blood to clot, then centrifuging
- (b) Adding anticoagulant to blood, then centrifuging
- (c) Removing only red blood cells
- (d) Adding thrombin to blood
Answer: (b) Anticoagulant blocks the clotting cascade; centrifugation then separates cells from plasma.
Q4. Serum is used in blood grouping tests because it contains:
- (a) Fibrinogen
- (b) Clotting factors
- (c) Antibodies (agglutinins)
- (d) Platelets
Answer: (c) Antibodies, Serum contains anti-A or anti-B antibodies. These cause agglutination in blood group testing.
Q5. Which statement about serum and plasma is INCORRECT?
- (a) Both contain albumin
- (b) Plasma contains fibrinogen; serum does not
- (c) Serum is used in blood transfusions instead of plasma
- (d) Serum is obtained from clotted blood
Answer: (c) Serum is not used for blood transfusions. Plasma (specifically, fresh frozen plasma) is used for transfusions.
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FAQs: Difference Between Serum and Plasma
Q1. What is the main difference between serum and plasma?
The main difference between serum and plasma is that plasma contains clotting factors like fibrinogen, while serum does not. Serum is plasma after the clotting proteins have been removed through the natural clotting process.
Q2. Which has fibrinogen serum or plasma?
Plasma contains fibrinogen. It is absent in serum because it is used up during coagulation to form fibrin. It is the major difference between serum and plasma.
Q3. How is plasma separated from blood?
An anticoagulant (EDTA, heparin, or sodium citrate) is added to blood to prevent clotting. The sample is centrifuged. Cells settle at the bottom; plasma stays on top.
Q4. Is serum used in blood transfusions?
No, for blood transfusions, plasma is used. Serum is generally used for diagnostic tests, blood grouping, and antitoxin preparation.
Q5. Why is serum preferred for diagnostic tests?
Serum lacks fibrinogen, which can interfere with certain biochemical and immunological assays. It also has a relatively higher antibody concentration, making it ideal for serological tests.
Written By: Saumya Sarin (Content Writer at Motion Education)
Reviewed By: Dr Vikas Kumar Tharwan (Biology Sr. Faculty)
Last Updated: June, 2026
