Serum, in a medical context, refers to the clear, yellowish liquid component of blood that remains after clotting. It is essentially blood plasma with the clotting proteins, such as fibrinogen, removed. This distinct composition makes serum a valuable biological sample for various medical applications, particularly in diagnostic testing and research.
What Serum Is and How It Forms
Serum is primarily composed of water, accounting for approximately 92% of its volume, along with dissolved substances. These include proteins like albumin and globulins (which encompass antibodies), electrolytes such as sodium, potassium, and chloride, hormones, and nutrients like glucose and amino acids.
Serum forms when a blood sample is collected and allowed to clot, typically over 30 minutes to an hour at room temperature. During this time, fibrinogen converts into an insoluble fibrin clot, trapping blood cells. After clotting, the sample is spun at high speed in a centrifuge. This separates the heavier clotted components from the lighter liquid portion, which is the serum.
Medical Uses of Serum
Serum plays a significant role in diagnostic testing, serving as a common sample type for identifying various medical conditions. For example, it is routinely used to detect antibodies, which can indicate past or current infections from pathogens like viruses or bacteria. Measuring hormone levels in serum helps diagnose endocrine disorders, while assessing markers of organ function, such as liver enzymes or kidney waste products, provides insight into organ health.
Beyond diagnostics, serum also has therapeutic applications. Antitoxins, for instance, are often administered as serum derived from immunized animals to provide passive immunity against bacterial toxins, such as those causing tetanus or diphtheria. This passive transfer of antibodies offers temporary protection. In some cases of immune deficiencies, serum containing antibodies may be used to bolster a patient’s immune response.
Serum is valuable in medical research, particularly as a component of cell culture media. It provides essential growth factors, hormones, and nutrients that support cell proliferation and maintenance outside the body. This application is fundamental for studying cellular processes, developing new drugs, and producing vaccines.
Serum Versus Plasma
The primary distinction between serum and plasma lies in the presence or absence of clotting factors. Plasma is the liquid component of blood that is obtained when clotting is prevented, meaning it still contains all clotting factors, including fibrinogen. In contrast, serum is the liquid that remains after blood has clotted, thus lacking these coagulation proteins.
Plasma is obtained by adding an anticoagulant to a blood sample immediately after collection, which prevents the formation of a clot. The anticoagulated blood is then centrifuged, separating the plasma from the blood cells.
For serum, the blood is allowed to clot without anticoagulants before centrifugation. Plasma is preferred for tests assessing blood clotting disorders or monitoring anticoagulant therapy due to its retained clotting factors. Conversely, serum is often chosen for biochemical tests, antibody detection, and drug level monitoring, where the absence of clotting factors provides a cleaner sample that does not interfere with the analysis.