Blood proteins, often called plasma proteins, are the thousands of different molecules suspended in the liquid portion of your blood. These substances make up about six to eight percent of the plasma’s volume. They are constantly circulating throughout the body, performing countless life-sustaining processes. Without them, the body could not properly transport nutrients, fight off disease, or stop bleeding. Their diversity and volume are necessary for maintaining stability and function across all organ systems.
Composition and Classification
Blood proteins are categorized into three main groups: albumin, globulins, and fibrinogen. Albumin is the most abundant, accounting for over half of the total protein mass. Most blood proteins, including albumin and fibrinogen, are manufactured and released into circulation by the liver.
Globulins are the second largest group, separated into alpha, beta, and gamma subgroups. Alpha and beta globulins are synthesized by the liver and function mainly as transport vehicles. Gamma globulins, also known as immunoglobulins or antibodies, are produced by specialized immune cells called plasma cells.
Fibrinogen is the least abundant category. This large, soluble protein is also produced in the liver, and its primary role is focused on clotting.
Primary Roles in the Body
The primary function of blood proteins is the transportation of substances that are otherwise difficult to move in the blood. Albumin acts as the primary carrier for materials like fatty acids, steroid hormones, and many medications. Alpha and beta globulins also contribute to transport, binding to and moving iron, lipids, and fat-soluble vitamins throughout the circulation.
Another role is maintaining fluid balance, driven by albumin’s influence on osmotic pressure. The size and concentration of albumin molecules keep water inside the blood vessels. This continuous pressure, known as oncotic pressure, prevents excessive fluid from leaking out of the capillaries and accumulating in the surrounding tissues.
The body’s defense mechanisms rely heavily on gamma globulins, or immunoglobulins. These specialized antibodies target foreign invaders, recognizing and binding to specific bacteria, viruses, and toxins. This action neutralizes them or marks them for destruction by other immune cells, forming the backbone of the adaptive immune system.
Hemostasis, the process of stopping bleeding, is managed by fibrinogen and other protein clotting factors. When a blood vessel is damaged, fibrinogen is converted into fibrin, an insoluble, thread-like protein. The fibrin threads interlace to form a stable meshwork that traps platelets and red blood cells, creating a clot to seal the wound.
Diagnostic Significance of Levels
Healthcare providers use blood tests to measure the total amount of protein and the levels of specific types to assess overall health. The Total Protein test is often included in routine metabolic panels. These tests help determine if the liver or kidneys are functioning correctly, or if chronic inflammation is present.
The Albumin/Globulin (A/G) ratio is a common diagnostic tool that compares albumin to combined globulins. An abnormal A/G ratio can indicate underlying conditions, prompting further investigation. For example, a low A/G ratio suggests reduced albumin synthesis (like in liver disease) or an overproduction of globulins (due to immune disorders or chronic infection).
Low levels of total protein or albumin may indicate the liver is not making enough protein (e.g., cirrhosis) or that the kidneys are losing too much protein through the urine. High total protein levels are associated with dehydration or increased globulin production, which occurs during inflammation or in certain bone marrow disorders. Specialized tests, such as serum protein electrophoresis, can further separate globulins to identify which group is elevated.