Serum is the clear, yellowish liquid portion of blood that remains after the blood has clotted. It is essentially blood plasma from which clotting factors and blood cells have been removed. This fluid is a complex mixture of various substances dissolved in water, making it a valuable sample for medical analysis.
The Key Difference Between Serum and Plasma
Understanding serum requires distinguishing it from plasma. The primary difference lies in the presence of clotting factors. When a blood sample is collected, it can either be allowed to clot naturally or be prevented from clotting through the addition of an anticoagulant.
If the blood is allowed to clot, the coagulation process occurs, where soluble proteins like fibrinogen are converted into insoluble fibrin strands, forming a clot. After clotting, the sample is centrifuged, spinning down blood cells and the clot. The remaining clear liquid at the top is serum, characterized by the absence of fibrinogen and other clotting factors. In contrast, plasma is obtained by centrifuging blood before it clots, meaning it still contains all clotting factors, including fibrinogen.
Major Components of Serum
Serum is predominantly composed of water (around 90%), containing numerous substances that reflect the body’s physiological state. These components are categorized into several groups, each with specific functions.
Proteins are a significant portion of serum, with albumin being the most abundant. Albumin helps maintain the osmotic pressure of blood, preventing fluid from leaking out of blood vessels, and also transports hormones and fatty acids. Globulins, including antibodies, play a central role in the immune system by defending against viruses and bacteria.
Serum also contains electrolytes, such as sodium, potassium, chloride, and calcium. These electrolytes are fundamental for maintaining the body’s fluid balance, pH levels, and proper nerve and muscle function. Nutrients like glucose and amino acids are present, serving as energy sources and building blocks for cells. Hormones, chemical messengers that regulate bodily functions, and metabolic waste products like urea and creatinine, removed by the kidneys, are also found in serum.
The Role of Serum in Diagnostics
Analyzing serum provides insights into an individual’s health, making it an important tool in medical diagnostics. The concentrations of various components in serum can indicate the presence of diseases or how well organs are functioning. For instance, common blood tests like a Comprehensive Metabolic Panel (CMP) or a Basic Metabolic Panel (BMP) measure the levels of electrolytes, glucose, and waste products in serum.
Measuring glucose levels in serum is routinely used to diagnose and monitor diabetes, as elevated levels can signal impaired sugar metabolism. Similarly, assessing serum creatinine and urea levels helps evaluate kidney function, as increased concentrations may suggest kidney impairment. Electrolyte imbalances, detected through serum analysis, can point to conditions like dehydration or kidney disorders. The presence and levels of specific antibodies in serum are also used in serology tests to detect past or current infections, or to confirm immunity after vaccination.