Blood is more than red and white cells. About half of it is a pale yellow liquid called plasma, and that liquid is crowded with proteins. These proteins do much of the day-to-day work of blood, from holding water inside your vessels to sealing a cut and flagging an infection. Because their levels shift with liver health, nutrition and inflammation, they are among the most common things measured on routine blood tests.
The Main Groups of Plasma Proteins
The most plentiful plasma protein is albumin, a small protein made by the liver. Everything else is grouped as globulins, a mixed family that includes carrier proteins, inflammation proteins and antibodies. In a purified protein fraction made from donated plasma, about 88% is albumin, about 12% is alpha and beta globulins, and no more than 1% is gamma globulin (antibodies).1DailyMed. PLASMANATE – plasma protein fraction (human) solution
Albumin, fibrinogen and most other plasma proteins are made in the liver. Antibodies are the exception: they come from immune cells called plasma cells. Since the liver does most of the manufacturing, a badly damaged liver can show up as falling plasma protein levels. The amount of a liver-made protein in your blood depends on how fast the liver releases it and how fast the body clears it away.2PubMed Central. Turnover Rates of Hepatic Collagen and Circulating Collagen-Associated Proteins in Humans with Chronic Liver Disease
On a standard report, many routine panels list total protein, albumin and sometimes globulin as a separate line. Globulin is often calculated as total protein minus albumin rather than measured directly. Some reports also give an albumin-to-globulin ratio, which compares the two groups. A single number outside the range means little alone, so doctors read it alongside other results.
You may also see “serum albumin” rather than “plasma albumin.” Plasma is the liquid part of blood with its clotting proteins still in it. Serum is what remains after blood has clotted, so fibrinogen has been used up. Most tests run on clotted samples, which is why reports say serum.
How Albumin Keeps Fluid in Your Blood Vessels
Dissolved proteins are the only substances in blood too large to slip through the tiny pores of capillary walls.3PubMed. The role of albumin in fluid and electrolyte balance They stay in the bloodstream and draw water toward themselves, a pull that keeps fluid from leaking into tissues.4PubMed. The role of albumin in fluid and electrolyte balance About 75% of that water-holding pull comes from albumin.5PubMed. The role of albumin in fluid and electrolyte balance
Blood pressure pushes fluid out toward the tissues, and the protein pull draws it back into the vessels. Swelling happens when the push wins because the pull has weakened.
Low albumin can show up as puffy ankles, swollen legs or fluid in the belly. Common causes include inflammation, liver problems, malnutrition, fluid losses and dilution from large amounts of IV fluid.6PubMed. The clinical significance of hypoalbuminaemia Poor diet alone lowers albumin slowly, while inflammation or IV fluids can drop it quickly.7PubMed. The clinical significance of hypoalbuminaemia
Low albumin is taken seriously because it is linked with a higher risk of complications and death.8PubMed. The clinical significance of hypoalbuminaemia That link mainly reflects the illnesses that cause the low level, not albumin itself.9PubMed. The clinical significance of hypoalbuminaemia Doctors usually treat the underlying cause rather than just giving albumin.
If your albumin is low, you can ask whether liver, kidney or inflammation tests were also checked. It is fair to ask if a recent illness, surgery or IV fluids might explain the result, and whether a repeat test is worth doing once you recover.
Carrier Proteins That Move Nutrients, Hormones and Medicines
Albumin is the blood’s all-purpose carrier. It can bind almost every known medicine, along with many supplements and toxic substances.10PubMed Central. Serum Albumin in Health and Disease: Esterase, Antioxidant, Transporting and Signaling Properties How much of a drug sticks to albumin helps decide how long it lasts and how much is free to act.11PubMed Central. Serum Albumin in Health and Disease: Esterase, Antioxidant, Transporting and Signaling Properties Albumin has a few main binding pockets, each preferring certain shapes of molecule.12PubMed Central. Binding and transport functions of human serum albumin and its clinical implications in liver disease: a narrative review It also carries fatty acids and bilirubin, the yellow waste from old red blood cells.13PubMed. Human serum albumin. Spectroscopic studies of binding and proximity relationships for fatty acids and bilirubin
That binding is why doses can matter when albumin is low. With less albumin, more of a bound drug floats free in the blood. Free drug is the active part, so effects can be stronger than expected. Doctors may adjust doses of some medicines in people with very low albumin, so tell your prescriber about liver disease or a recent severe illness.
Globulins carry more specialised cargo. Haptoglobin grabs hemoglobin released when red cells break down, which prevents the iron loss, kidney damage and inflammation that loose hemoglobin can cause.14PubMed Central. Quantification of human plasma metalloproteins in multiple sclerosis, ischemic stroke and healthy controls reveals an association of haptoglobin-hemoglobin complexes with age Ceruloplasmin, a copper-carrying protein, helps load iron onto transferrin, the protein that delivers iron to cells.15PubMed. Iron uptake and transfer from ceruloplasmin to transferrin Apolipoproteins wrap cholesterol and fats into particles and help move them between tissues.16PubMed. Plasma lipoproteins: apolipoprotein structure and function
Fats do not dissolve in watery blood, so they travel in protein-wrapped particles. The HDL and LDL on your report are such particles, and their proteins act like address labels guiding where the fats go.
Antibodies and the Complement System
Antibodies, also called immunoglobulins, come in five classes: IgG, IgA, IgM, IgD and IgE.17Lumen Learning. What Are Plasma Proteins and Why Are They Important? IgG makes up about 80% of all antibodies.18Lumen Learning. What Are Plasma Proteins and Why Are They Important? One end of each antibody fits a particular target, while the other end decides how the immune system attacks it.19Lumen Learning. What Are Plasma Proteins and Why Are They Important?
The classes have different specialties. IgM appears first in a new infection. IgG gives long-term protection and crosses the placenta to the baby. IgA guards moist surfaces such as the gut and airways, and IgE drives allergic reactions.
These show up in tests. Immunity checks after vaccines often measure IgG to a specific germ, and total IgE may be checked when allergies are suspected. Low antibody levels can explain repeated infections.
Complement is a set of plasma proteins that activate each other in a chain reaction.20PubMed. Complement and its role in innate and adaptive immune responses They coat germs so white cells can eat them more easily, and they draw white cells to the site.21PubMed. The role of the complement system in innate immunity The final complement proteins form a ring that punches holes in invaders.22PubMed. The role of the complement system in innate immunity Complement also produces signals that cause the redness and swelling of inflammation.23PubMed. Complement and its role in innate and adaptive immune responses
Fibrinogen and How Blood Clots
Fibrinogen is a liver-made protein that circulates dissolved in plasma.24Grifols. Fibrinogen: Functions, Uses & Disorders When a vessel is injured, the clotting enzyme thrombin snips fibrinogen into fibrin.25PubMed Central. Fibrinogen and fibrin in hemostasis and thrombosis Fibrin pieces lock together like knobs into holes and build long fibers.26PubMed Central. Fibrinogen and fibrin in hemostasis and thrombosis Another clotting protein then welds the fibers, making the clot stable.27PubMed. Why fibrin biomechanical properties matter for hemostasis and thrombosis The fibrin mesh also supports wound healing.28Grifols. Fibrinogen: Functions, Uses & Disorders
After a cut, platelets form a soft plug within seconds. Fibrin threads then weave through and around the plug. The mesh traps red cells, which gives a scab its colour. Without enough fibrinogen, bleeding lasts longer. Other plasma proteins act as brakes: by blocking enzymes, they help control clotting, complement and inflammation, and they stop clotting from spreading where it is not needed.29PubMed. Plasma protease inhibitors in mouse and man: divergence within the reactive centre regions
Too much clotting is its own problem. The same mesh can form inside vessels and block blood flow, which causes deep vein clots, strokes and heart attacks. High fibrinogen during inflammation may make clots more likely.
CRP and Other Proteins That Rise With Inflammation
During infection, injury or inflammation, the liver boosts production of acute phase proteins, which are the inflammation proteins. The best known is C-reactive protein (CRP). CRP and serum amyloid A can rise as much as 1,000-fold.30PubMed. Properties of four acute phase proteins: C-reactive protein, serum amyloid A protein, alpha 1-acid glycoprotein, and fibrinogen Fibrinogen and alpha-1 acid glycoprotein rise only about two- to fourfold.31PubMed. Properties of four acute phase proteins: C-reactive protein, serum amyloid A protein, alpha 1-acid glycoprotein, and fibrinogen The signal comes from immune messengers released during inflammation.32PubMed. Properties of four acute phase proteins: C-reactive protein, serum amyloid A protein, alpha 1-acid glycoprotein, and fibrinogen
Some proteins drop during inflammation, and albumin is one of them. When CRP is high, a low albumin is more likely to reflect inflammation than poor diet.33PubMed. The clinical significance of hypoalbuminaemia These proteins show that something is inflamed, not what or where.34PubMed Central. Acute phase reaction and acute phase proteins
A mildly raised CRP can come from a cold, an injury or recent exercise. Very high values often suggest bacterial infection or major inflammation. Doctors repeat CRP to see whether treatment is working. A separate high-sensitivity CRP test is used for heart risk.
Protein Electrophoresis and Myeloma Screening
Serum protein electrophoresis spreads blood proteins out into bands for albumin and each globulin group.35PubMed Central. The Role of Serum Protein Electrophoresis in the Detection of Multiple Myeloma: An Experience of a Corporate Hospital An unusual sharp spike, called an M protein, signals one cell line making a single antibody in excess.36PubMed Central. The Role of Serum Protein Electrophoresis in the Detection of Multiple Myeloma: An Experience of a Corporate Hospital This pattern is the hallmark of multiple myeloma, a blood cancer of plasma cells.37PubMed Central. The Role of Serum Protein Electrophoresis in the Detection of Multiple Myeloma: An Experience of a Corporate Hospital
Doctors order the test for unexplained bone pain or fractures, or for anemia, kidney problems or high calcium without a clear cause. A high total protein or globulin on routine blood work can also prompt it.
An M protein can also come from a harmless-for-now condition called MGUS.38PubMed Central. The Role of Serum Protein Electrophoresis in the Detection of Multiple Myeloma: An Experience of a Corporate Hospital Full screening pairs electrophoresis with immunofixation and a free light chain blood test.39PubMed. Laboratory testing requirements for diagnosis and follow-up of multiple myeloma and related plasma cell dyscrasias
After an abnormal band, further tests identify which antibody type is involved. A bone marrow biopsy may follow to count plasma cells. Many people with MGUS only need regular monitoring.
Plasma Proteins Used as Medicines
IVIG is a medicine made from pooled antibodies of at least 1,000 and up to 100,000 healthy donors.40PubMed Central. The Production Processes and Biological Effects of Intravenous Immunoglobulin About 80% of the plasma comes from dedicated plasma donors and 20% from blood donors.41PubMed Central. The Production Processes and Biological Effects of Intravenous Immunoglobulin IVIG protects people born with or who develop weak antibody defenses.42PubMed. Purification of intravenous immunoglobulin G from human plasma–aspects of yield and virus safety It is increasingly used for autoimmune and inflammatory diseases.43PubMed. Purification of intravenous immunoglobulin G from human plasma–aspects of yield and virus safety
Albumin is also a treatment. Infusions can restore fluid-holding pull after severe blood loss or burns, and doctors use it in some complications of liver disease.
People with hemophilia A lack clotting factor VIII and receive it from plasma or lab-made products. In one major trial, newly treated patients on lab-made factor VIII developed blocking antibodies more often than those on plasma-derived factor.44PubMed Central. Immune Responses to Plasma-Derived Versus Recombinant FVIII Products
Making these medicines needs huge volumes of donated plasma. Plasma donation returns red cells to the donor, so it can be repeated more often than whole blood donation.
How Plasma Proteins Change With Pregnancy and Age
In normal pregnancy, about 10% of plasma proteins measured change in level as pregnancy progresses.45PubMed Central. The Maternal Plasma Proteome Changes as a Function of Gestational Age in Normal Pregnancy: a Longitudinal Study Placental proteins such as PlGF and PAPP-A rise more than fivefold.46PubMed Central. The Maternal Plasma Proteome Changes as a Function of Gestational Age in Normal Pregnancy: a Longitudinal Study
In pregnancy, plasma volume rises, which dilutes albumin slightly. PAPP-A is used in first-trimester screening tests, and PlGF tests help assess preeclampsia risk. A result should therefore be compared with ranges suited to your age and pregnancy status.