Blood, a fluid, circulates throughout the body, delivering substances and removing waste. This fluid is composed of cells suspended in a liquid matrix. Plasma and serum are two terms that frequently arise when discussing blood components. While both are derived from blood, they are distinct components with different compositions and uses.
What is Plasma?
Plasma is the yellowish liquid remaining after blood cells are removed. To obtain plasma, whole blood is collected and treated with an anticoagulant, a substance that prevents clotting. The treated blood is then centrifuged, separating heavier blood cells to the bottom, leaving the lighter plasma as the top layer. Plasma constitutes about 55% of the total blood volume and is approximately 92% water.
Plasma contains dissolved substances, including proteins like albumin, globulins, and fibrinogen. It also carries electrolytes, hormones, nutrients, and waste products. Plasma’s function is to transport these components throughout the body, contributing to the maintenance of fluid balance and bodily functions.
What is Serum?
Serum is the liquid obtained after blood has clotted. Unlike plasma, no anticoagulant is added. The sample is left undisturbed, allowing natural clotting. After clotting, the sample is centrifuged, which separates the solid clot (containing blood cells and clotted proteins) from the liquid serum.
A difference in serum’s composition is the absence of fibrinogen and other clotting factors. These proteins are consumed or removed during the clotting process, as fibrinogen is converted into fibrin, which forms the clot. Despite lacking clotting factors, serum contains other proteins, antibodies, hormones, electrolytes, and other substances present in blood. The study of serum is known as serology.
Key Differences and Their Medical Applications
The distinction between plasma and serum lies in the presence or absence of clotting factors, particularly fibrinogen. Plasma contains these clotting factors because it is separated from blood before coagulation, typically by adding an anticoagulant. In contrast, serum is collected after blood has clotted, meaning fibrinogen and other clotting proteins have been used up or removed. This difference in composition dictates their specific uses in medicine and diagnostics.
Plasma is used for therapeutic purposes, such as transfusions, especially for patients who have lost significant blood volume due to trauma or severe burns. It is also administered to individuals with bleeding disorders or liver disease, as it provides the clotting factors to help stop bleeding. Specific proteins derived from plasma are used in therapies for conditions, including certain autoimmune disorders and immunodeficiencies.
Serum, lacking clotting factors, is valuable in diagnostic testing, as the absence of these factors prevents interference with many laboratory assays. It is used to detect antibodies for infectious diseases, assess hormone levels, measure electrolytes, and identify biomarkers for health conditions. The choice between using plasma or serum for a medical application or diagnostic test depends on the specific information required or the treatment being administered.