Immunoglobulins, also called antibodies, are molecules produced by white blood cells that help your body defend against infections and cancer. Their primary function is to bind to foreign cells like bacteria and viruses. This binding helps neutralize the foreign cell and signals to your white blood cells to destroy them.

Humans have five types of immunoglobulins. Immunoglobulin levels that are higher or lower than normal can indicate an underlying medical condition.

For example, a type of cancer called multiple myeloma is often associated with elevated levels of immunoglobulins, and kidney disease sometimes causes low levels. Doctors sometimes treat low immunoglobulin levels with an intravenous (IV) immunoglobulin infusion.

Read on to learn more about immunoglobulins, including how they help your body mount a defense against infections and why doctors use tests to measure your immunoglobulin levels.

Immunoglobulins are Y-shaped molecules made up of sugar and protein produced by plasma cells, a type of white blood cell. They have three main functions:

  1. preventing foreign invaders from entering cells by neutralizing them
  2. coating foreign invaders to tag them for destruction by white blood cells called macrophages
  3. triggering destruction of foreign invaders by stimulating other immune responses

The tip of immunoglobulins contains a highly variable region called a paratope. The paratope binds to sections of foreign molecules called epitopes like a lock and key.

The tip of the paratope contains a highly variable region that allows for your body to produce millions of types of antibodies. Each antibody only binds with one particular type of foreign molecule.

What are plasma cells?

Plasma cells are activated B cells. They have the capacity to generate mass quantities of immunoglobulins that are programmed to recognize a specific epitope (foreign molecule).

Your blood consists of three types of blood cells:

All blood cells come from special cells called hematopoietic stem cells found in your bone marrow. These cells can become two other types of cells called myeloid stem cells or lymphoid stem cells.

Lymphoid stem cells can become three types of white blood cells that play critical roles in your adaptive immunity:

  • Natural killer cells: contain enzymes to destroy cancer cells or viruses
  • T cells: destroy infected cells and activate other immune cells
  • B cells: become plasma cells when activated by foreign invaders and produce Immunoglobulins

Immunoglobulins are made up of two molecules called light chains and two called heavy chains. Five types of immunoglobins are found in humans. They’re named after the type of heavy chain they contain:

  • IgM: Provides rapid defense against infectious diseases.
  • IgG: Provides most of the immunoglobin-based immunity against foreign molecules but has a slower effect than IgG.
  • IgA: Provides defense against infectious agents and is found mostly in your mucus membranes. It protects the surfaces of your respiratory, digestive, and urinary systems.
  • IgE: Provides protection against parasites. It also triggers histamine release from white blood cells called mast cells and basophils to trigger allergic reactions.
  • IgD: Has a largely unknown function. It may serve as a receptor on B cells that haven’t been previously exposed to foreign molecules.

Immunoglobulin levels are useful biomarkers for monitoring many different diseases, including immunodeficiencies and autoimmune diseases.

Your doctor may recommend testing your immunoglobulin levels if immunodeficiency runs in your family or if you have symptoms of a condition associated with atypical immunoglobulin levels like persistent diarrhea or unexplained weight loss.

Low immunoglobulin levels

Low immunoglobulin levels suggest that your immune system is not functioning optimally.

Conditions associated with low immunoglobulin levels include:

Some people are born with lower-than-normal immunoglobulin levels. IgA deficiency occurs in about 1 in 700 people, according to the National Health Service.

High immunoglobulin levels

Elevated immunoglobulin levels are seen in people with conditions such as:

Antibody deficiency disorders

Some people do not produce immunoglobulins or do not produce as many immunoglobulins as they typically should. These conditions are called antibody deficiency disorders.

They may present shortly after birth with recurrent infections. These conditions are often treated with intravenous immune globulin (IVIG) where immunoglobulins are infused through a vein.

Other people have autoimmune conditions where they produce immunoglobulins against their own cells. This happens through a process called molecular mimicry.

In molecular mimicry, the paratopes of circulating immunoglobulins that are primed against an earlier infection closely resemble innocent epitopes on the surface of healthy cells.

IVIG is often used to treat these conditions, which include:

immune thrombocytopeniaautoimmune destruction of platelets
autoimmune hemolytic anemiaautoimmune destruction of red blood cells
Guillain-Barré syndromeautoimmune destruction of nerves that control breathing
chronic inflammatory demyelinating polyneuropathyautoimmune destruction of your nerves’ protective coating

Doctors often order tests to check circulating levels of IgA, IgG, and IgM to measure your immune function. IgD isn’t routinely tested, and its function isn’t fully understood.

Here’s a look at immunoglobulin tests and what a low or high score could indicate. Reference ranges are based on the 2.5th and 97.5th percentiles. Each laboratory establishes its own reference range, so these values are estimates.

Immunoglobulin testApproximate reference rangesConditions associated with a low scoreConditions associated with a high score
IgA test0.8 to 3.0g/L• some types of leukemia
• kidney damage
• intestinal problems
• increased risk of severe reaction after blood transfusion
• low or lack of IgA production from birth
monoclonal gammopathy of unknown significanc (MGUS)
• multiple myeloma
• some autoimmune diseases like rheumatoid arthritis
IgD test0.003 to 0.03g/L• researchers are still trying to understand the significance of low IgD• may rarely suggest multiple myeloma
IgE test0.0002 to 0.002g/L• can occur with a rare disease called ataxia-telangiectasiaparasitic infection
allergic reactions
atopic dermatitis
• some cancers
• some autoimmune diseases
• rarely multiple myeloma
IgG test6.0 to 16.0g/L• Waldenstrom’s macroglobulinemia
• leukemia
• kidney damage
• rarely, people are born without IgG immunoglobulin
• chronic infections like AIDS
• multiple myeloma
• chronic hepatitis, multiple sclerosis
IgM test0.4 to 2.5g/L• multiple myeloma
• leukemia
Waldenstrom’s macroglobulinemia
• early viral hepatitis
• rheumatoid arthritis
• kidney damage
• parasitic infection
• new infection
Thyroid-stimulating immunoglobulin (TSI) hormoneUnder 0.54 IU/LTSI is a type of IgG that tells the thyroid to release more thyroid hormones. Higher than normal levels may indicate Graves’ disease

Immunoglobulins are molecules produced by plasma cells following B cell activation due to exposure to a foreign agent. B cells are white blood cells of lymphoid lineage.

Many different health conditions are associated with high or low immunoglobulin levels. A doctor may recommend testing your immunoglobulin levels if you have a family history of immunodeficiency or symptoms of a condition associated with atypical immunoglobulin levels.