Plasma Proteins

Key points

• • Albumin is the most abundant plasma protein; it is made by the liver, holds water inside the vessels by exerting oncotic pressure, and carries many poorly soluble substances.
• • A fall in albumin, from liver disease, kidney loss or malnutrition, lowers oncotic pressure and lets fluid leak into the tissues, causing oedema.
• • The globulins include alpha and beta globulins (transport and clotting proteins) and gamma globulins, which are mainly the antibodies (immunoglobulins) made by plasma cells.
• • Fibrinogen is a plasma protein made by the liver that is converted to fibrin to form a clot; serum is plasma with the clotting proteins removed.
• • Separating plasma proteins by electrophoresis gives a pattern of bands whose changes help point to diseases such as chronic inflammation or myeloma.
• • Albumin also carries unconjugated bilirubin, free fatty acids, calcium and many drugs, so a low albumin level changes how much of these is free and active.