Serum, in medical contexts, refers to the clear, yellowish liquid portion of blood that remains after the clotting process has occurred. It is a complex mixture containing various proteins, electrolytes, hormones, and antibodies, among other substances. This fluid component is distinct from whole blood because it lacks blood cells and the factors involved in coagulation.
What Serum Contains and How It’s Prepared
Serum is essentially blood plasma with clotting proteins, such as fibrinogen, removed. Unlike plasma, which contains these coagulation factors, serum lacks them. This absence is a defining characteristic, achieved through a specific preparation process.
To obtain serum, a blood sample is collected in a tube without any anticoagulant. The blood is then allowed to clot naturally, typically by leaving it undisturbed for 15 to 60 minutes. During this time, clotting factors interact to form a clot, trapping blood cells and platelets within it.
After clotting, the sample undergoes centrifugation, where it is spun at high speeds for 10 to 15 minutes. This separates the heavier clotted blood components from the lighter liquid serum, which forms the supernatant layer at the top. The clear serum is then extracted and can be stored for later analysis, typically at -20°C or lower.
Medical Applications of Serum
Serum is widely used in medical diagnostics and research due to its stable composition and the absence of clotting factors, which can interfere with certain tests. Its stability makes it suitable for measuring a broad range of analytes, including hormones, electrolytes, enzymes, and various proteins. For instance, serum tests are performed to assess hormone levels, such as thyroid hormones or cortisol, aiding in the diagnosis of endocrine disorders.
The fluid is also instrumental in detecting antibodies and antigens, fundamental for diagnosing infectious diseases like hepatitis, HIV, or syphilis, as well as autoimmune conditions such as rheumatoid arthritis. This type of testing, known as serology, provides insights into a patient’s immune response and can be used in population-level studies to track disease prevalence. Serum also plays a role in medical research, including drug development and the identification of biomarkers for various diseases, such as cancer. Its use in cell culture media, such as human serum, offers a more relevant model for studying human biological processes compared to animal-derived alternatives.