null
Serum vs. Plasma: A Deep Dive into Their Molecular Makeup and Implications for ELISA

Serum vs. Plasma: A Deep Dive into Their Molecular Makeup and Implications for ELISA

Blood plasma and serum are essential components of blood and have distinct molecular compositions and uses in the medical and research fields. This article aims to elucidate the differences between serum and plasma and respond to the most frequently asked questions.

What is Serum vs Plasma?

Blood consists of red and white cells, platelets, and a liquid portion, known as plasma. When blood is collected and coagulates, the solid components, such as fibrin and blood cells, are separated, leaving a clear yellowish fluid known as serum.

In contrast, plasma is the fluid that remains when an anticoagulant is used to prevent the blood from clotting. The primary difference between serum and plasma lies in the clotting factors. Plasma contains clotting factors, while serum is essentially plasma without these factors1.

Both serum and plasma contain water, electrolytes, hormones, waste products, nutrients, gases, and proteins. However, plasma also contains fibrinogen and other coagulation factors that are used in clot formation. A half-life molecule, for instance, could exist differently in plasma and serum due to these differences. Its half-life could potentially be extended or reduced based on the presence or absence of these coagulating factors.

Schematic of serum vs plasma sample type

Schematic: Serum vs Plasma

How to Collect Serum vs Plasma?

The collection process for serum involves allowing the blood to clot, usually taking about 30 minutes, then centrifuging the sample to separate the serum.

The collection process for plasma involves adding an anticoagulant, such as heparin or EDTA, before the sample is centrifuged. The upper layer of fluid, the plasma, is then collected2.

Materials Required:

  • Blood collection tubes with an anticoagulant (e.g., EDTA, heparin, or sodium citrate)
  • Sterile needle and syringe or vacutainer system
  • Centrifuge
  • Pipettes
  • Personal protective equipment (gloves, lab coat, eye protection)

How to Collect Serum?

The table below outlines the key steps in collecting serum.

Step Procedure

1

Put on personal protective equipment.

2

Clean the venipuncture site using an appropriate antiseptic.

3

Perform venipuncture using a sterile needle and syringe or a vacutainer system and collect the blood into the tube.

4

Leave the tube undisturbed at room temperature to allow the blood to clot. This usually takes 15–30 minutes.

5

After clotting, centrifuge the tube at 1,000–2,000 x g for 10 minutes in a refrigerated centrifuge to separate the serum.

6

Carefully pipette the serum (the top layer) into a new tube, ensuring not to disturb the clot.

7

Label the new tube as "serum"​2

How to Collect Plasma?

The table below outlines the key steps in collecting plasma.

Step Procedure

1

Put on personal protective equipment.

2

Clean the venipuncture site using an appropriate antiseptic.

3

Perform venipuncture using a sterile needle and syringe or a vacutainer system and collect the blood into the tube containing the anticoagulant.

4

Invert the tube 5-10 times immediately after collection to mix the anticoagulant with the blood, thereby preventing clotting.

5

Ensure that the tube is filled completely to avoid a dilution factor that is excessive for the total specimen volume.

6

Centrifuge the sample within two hours of venipuncture or as indicated in the test requirements to separate the plasma from the cells.

7

Carefully pipette the plasma (the top layer) into a new tube, ensuring not to disturb the buffy coat or red blood cells.

8

Label the new tube as "plasma" and indicate the type of anticoagulant used​1.

Levels of Zinc in Serum & Plasma

Plasma and serum zinc are two forms in which zinc can be found in the human body. Zinc is an essential mineral that plays a crucial role in various physiological processes. Plasma zinc refers to the concentration of zinc found in the liquid component of blood, which is obtained when anticoagulants are added to the blood sample. On the other hand, serum zinc refers to the concentration of zinc in the clear, yellowish fluid that remains after the blood has clotted and the cells have been removed.

Both plasma and serum zinc levels are commonly measured to assess a person's zinc status. However, there can be slight differences in their concentrations due to the clotting process involved in serum separation. Plasma zinc levels tend to be slightly higher than serum zinc levels because some zinc is released from the clot during the separation process.

Measuring plasma or serum zinc levels can provide valuable information about an individual's zinc status. Zinc deficiency can lead to various health issues, such as impaired immune function, growth retardation, and delayed wound healing. Conversely, excessive zinc levels can also have detrimental effects on health. Therefore, monitoring plasma or serum zinc levels is important in identifying deficiencies or excesses and determining the appropriate interventions, such as dietary modifications or zinc supplementation, to maintain optimal zinc balance in the body.

Which Phlebotomy Tubes Produce Plasma vs Serum?

Different colored tops of phlebotomy tubes indicate the type of additive in the tube. For plasma tubes with light blue, green, or lavender tops are generally used, as these contain anticoagulants. For serum collection, red or gold (also known as tiger) top tubes are typically used, which lack anticoagulants.

Why are Enzymes Measured in Serum vs Plasma?

Enzyme measurements can be done in either serum or plasma. However, some enzymes, like potassium-dependent enzymes, can be affected by the anticoagulant in the plasma. Therefore, serum is usually preferred for enzyme assays.

Using ELISA to measure analytes in Serum & Plasma

ELISA (Enzyme-Linked Immunosorbent Assay) is a widely used method for measuring analytes in serum and plasma. By utilizing specific antibodies that bind to the target analyte, ELISA enables the detection and quantification of proteins, hormones, and other molecules in these biofluids. Through a series of steps involving antibody binding, washing, enzyme labeling, and signal measurement, ELISA provides a sensitive and reliable technique to assess analyte concentrations in serum and plasma samples. This valuable tool aids in research, clinical, and diagnostic applications, offering insights into the levels of specific molecules and their implications for health and disease.

References

Lippi, G., & Plebani, M. (2012). Serum versus plasma: which is the better choice?. Clinical Chemistry and Laboratory Medicine, 50(9), 1523-1524. doi:10.1515/cclm-2012-0099

Van Der Meer, P. F., & Pietersz, R. N. (2016). Blood plasma and serum components. Wiley Encyclopedia of Blood Transfusion. doi:10.1002/9781119301141.wbebt032

Lowe, N. M., & Fekete, K. (2009). Methods of assessment

Written by Sean Mac Fhearraigh

Seán Mac Fhearraigh PhD is a co-founder of Assay Genie. Seán carried out his undergraduate degree in Genetics at Trinity College Dublin, followed by a PhD at University College Dublin. He carried out a post-doc at the Department of Genetics, University of Cambridge. Seán is now Chief Technical Officer at Assay Genie.

Additional Resources


27th Jun 2023 Sean Mac Fhearraigh

Recent Posts