Blood plasma is a vital, yet often overlooked, component of human blood that plays a crucial role in maintaining overall health and facilitating essential physiological processes.
Representing approximately 55% of total blood volume, plasma is a complex liquid medium composed predominantly of water but also enriched with proteins, nutrients, hormones, and other substances.
Composition and Physical Characteristics
Plasma is a pale yellow, straw-colored fluid that contains about 90% to 92% water. The remainder consists of dissolved solids which include proteins, electrolytes, nutrients, gases, and waste products. Key plasma proteins encompass albumin, globulins, and fibrinogen.
Albumin, produced by the liver, is the most abundant plasma protein and is essential for maintaining oncotic pressure, which helps keep fluid within blood vessels and prevents swelling. Globulins encompass a variety of proteins including antibodies (immunoglobulins) that are integral to immune defense. Fibrinogen is critical in blood clotting processes, ensuring fluid stops escaping damaged vessels.
Aside from proteins, plasma carries crucial electrolytes such as sodium, potassium, calcium, magnesium, and bicarbonate ions, helping regulate nerve and muscle function, hydration, blood pH, and cellular metabolism. Additionally, plasma transports glucose, lipids, vitamins, hormones, and dissolved gases like oxygen and carbon dioxide, facilitating cellular respiration and energy metabolism throughout the body.
Physiological Functions
Blood plasma serves multiple indispensable functions. It acts as the transport medium for red blood cells, white blood cells, and platelets, which are suspended within this fluid. Plasma’s transport role extends to nutrients absorbed from the digestive system, distributing them to tissues, and carrying metabolic waste products to organs responsible for excretion, such as the kidneys and lungs.
Immunologically, plasma contains antibodies and complement proteins that target pathogens and help regulate inflammatory responses. The clotting factors dissolved in plasma activate when vascular injury occurs, catalyzing a biochemical cascade that results in clot formation to prevent excessive bleeding.
Plasma volume regulation is also crucial for maintaining blood pressure and volume homeostasis. Its osmotic properties draw water into blood vessels, balancing fluid exchange with surrounding tissues. This osmotic effect is vital for preventing edema and ensuring optimal circulation.
Clinical Significance and Applications
Plasma plays a vital role in both diagnostics and therapy in modern medicine. As the cell-free liquid component of blood, plasma contains electrolytes, proteins (including clotting factors and immunoglobulins), hormones and metabolic by-products. Measurement of its composition—such as electrolyte concentrations, albumin and globulin levels, or the presence of disease-specific biomarkers—provides key insights into a patient’s electrolyte balance, nutritional/protein status, liver and kidney function, and possible metabolic or infectious disease processes.
Plasma transfusion: Units of donor plasma (commonly termed fresh frozen plasma, FFP) are administered when there is a documented deficiency of clotting factors or a clinically significant coagulopathy in the setting of active bleeding. Guidelines emphasise that transfusion of plasma is not indicated simply to correct mildly abnormal coagulation tests in the absence of bleeding.
Therapeutic plasma exchange (TPE, or plasmapheresis): In this procedure, a volume of patient’s plasma is removed via an apheresis machine, and the red blood cells and other cellular components are returned to the patient along with a replacement fluid (such as 5% albumin or sometimes donor plasma). The goal is to remove pathogenic substances (for example auto-antibodies, immune complexes, or abnormal proteins) from the circulation more rapidly than the body can clear them.
Plasma donation / derivation of plasma-derived therapies: Donor plasma provides raw material for manufacturing certain biologic medications, including immunoglobulin preparations and coagulation factor concentrates (used in immune deficiencies or inherited bleeding disorders). While plasma donation is indeed an important resource, the specific therapeutic manufacturing uses must be distinguished from direct plasma transfusion or exchange.
Dr Dobri Kiprov, an immunologist and pioneer in therapeutic apheresis, explains the TPE process as follows: “When someone undergoes Therapeutic Plasma Exchange, their blood is passed through an apheresis machine, their filtered plasma is removed and discarded, and then their red blood cells (and other cellular components) are returned to them, accompanied by the infusion of a replacement fluid such as plasma or albumin.”
Blood plasma is an indispensable component of blood, acting as a carrier for cells, nutrients, proteins, and biochemical substances essential to life. Its balanced composition sustains circulatory stability, immunity, and metabolic processes. Medical advancements in plasma therapies and diagnostic techniques continue to expand understanding and utilization of this crucial fluid. Continued research and plasma donation efforts remain vital to improving treatment outcomes and supporting patients worldwide.
