When we talk about blood analysis, we usually think about what happens to this “sample" obtained during the extraction. They do take a blood sample from us, but then, depending on the tests to be analyzed, this original sample can become other types of samples. Today we explain two of them: plasma and serum. Although both are liquid components derived from blood, they have fundamental differences in their composition, method of obtaining, and the analyses they allow.

What is plasma?

The plasma is a transparent or slightly yellowish liquid where the cellular elements, erythrocytes, leukocytes, platelets are suspended and it contains all the coagulation factors. It represents approximately 55% of the total blood volume. Its main function is, to act as a transport medium for various elements within the bloodstream such as cells, proteins, hormones, and other nutrients.

It is obtained by centrifuging a blood sample collected in a tube with anticoagulant, such as EDTA, citrate, or heparin, which prevents coagulation and allows separation of the cellular elements from the liquid component.

What is analyzed in plasma?

• Electrolytes
• Hormones
• Plasma proteins
• Coagulation parameters (PT, aPTT…)
• Inflammatory markers

Plasma is especially useful in emergency contexts, as it can be processed quickly without needing to wait for the sample to clot.

What is serum?

Serum is the transparent liquid part of the blood that remains after removing blood cells and coagulating proteins (coagulation factors). It is also called blood serum.

It is obtained by allowing the blood to clot (without anticoagulants) for about 30-60 minutes and then centrifuging it to separate the liquid part from the clot. Often, tubes with a separator gel are used to facilitate the separation between serum and clot.

What is analyzed in serum?

• Lipid profile
• Liver enzymes
• Serology (antibodies)
• Immunological tests
• Tumor markers

Serum is ideal for biochemical, hormonal, or immunological studies, such as those performed in routine check-ups.

Key differences between plasma and serum

Characteristic	Plasma	Serum
Presence of coagulation factors	Yes	No
Method of obtaining	Blood with anticoagulant + centrifugation	Blood without anticoagulant + clotting + centrifugation
Processing time	Immediate	Requires 30-60 minutes
Typical color	Slightly yellow, may have slight turbidity.	Clearer (may vary depending on lipids)
Main uses	Coagulation, emergencies, transfusions	Biochemistry, serology, immunology

 

Why is this distinction important?

It is important to distinguish them because although many of the parameters analyzed in the Laboratory could be performed on both types of samples, we must prepare the appropriate sample type depending on which sample the Laboratory requires. Other times, it is not possible to perform the analysis on both types of samples, only on one of them; for example, all coagulation parameters can only be determined in plasma. Using the wrong type can alter or even invalidate the results. That is why clinical laboratories carefully select the type of tube and processing method according to the analysis needed.

Additionally, from a clinical point of view, plasma is also used in transfusions, especially in patients with coagulation disorders or hemorrhages, while serum is the most commonly used sample in the Laboratory because it is easier to handle.

 

👉 Direct link to our post on Instagram: