Immunoglobulins, or antibodies, are produced by white blood cells. They help your body defend against infections and conditions like cancer. Tests measure them and help diagnose these medical conditions.

Immunoglobulins, also called antibodies, are molecules produced by white blood cells that help your body defend against infections, autoimmune diseases, cancer, and other conditions. They bind to foreign cells like bacteria and viruses to help your white blood cells destroy the foreign cells.

Doctors may order immunoglobulin tests to help diagnose infections or conditions like cancer.

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:

  • neutralizing foreign invaders to prevent them from entering cells
  • coating foreign invaders as a tagging method for white blood cells called macrophages to easily identify them for destruction
  • triggering destruction of foreign invaders by stimulating other immune responses

The tip of immunoglobulins contains an area that binds to sections of foreign molecules like a lock and key.

Your immunoglobulins can produce millions of types of antibodies. Each antibody only binds with one particular type of foreign molecule.

Doctors order immunoglobulin tests to look for immunoglobulin levels that are higher or lower than normal because these levels can mean you have a medical condition.

For example, a type of cancer called multiple myeloma is often associated with higher levels of immunoglobulins, and kidney disease sometimes causes lower levels.

What are plasma cells, and why are they important?

All blood cells come from special cells called hematopoietic stem cells found in your bone marrow. These stem 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

Plasma cells are activated B cells or T cells. They can create millions of immunoglobulins that are programmed to recognize specific foreign molecules that may enter your bloodstream.

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 well.

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 (NHS).

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 tests and what they mean

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-telangiectasia
• some cancers
• autoimmune disorders
• immune deficiencies
parasitic infection
allergic reactions
atopic dermatitis
• some cancers
• some autoimmune diseases
• rarely multiple myeloma
IgG test6.0 to 16.0g/L• Waldenstrom macroglobulinemia
• leukemia
• kidney damage
• celiac disease
• autoimmune disease
• certain adult malignancies
• 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 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

High immunoglobulin levels

Elevated immunoglobulin levels may be seen in people with conditions such as:

Low immunoglobulin levels

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

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.

Atypical immunoglobulin levels

Unusual results may also mean an individual has an autoimmune condition. These conditions occur when their body produces immunoglobulins that attack their own cells rather than foreign, invading cells. If this happens, it’s called molecular mimicry.

In molecular mimicry, the tips of circulating immunoglobulins that are primed against an earlier infection closely resemble tips on the surface of your healthy cells and the immunoglobulins produced attack those healthy cells.

Conditions where your immunoglobulins attack your healthy cells include:

These conditions may also be treated with IVIG.

What is the main function of immunoglobulins?

The main function of immunoglobulins is to help your body defend against infections, cancer, autoimmune diseases, and other conditions.

What are the 5 major immunoglobulins?

The five main immunoglobulins are:

  • IgM: Provides rapid defense against infectious diseases.
  • IgG: Provides most immunoglobin-based immunity against foreign molecules but has a slower effect than IgM.
  • 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 have not been previously exposed to foreign molecules.

What do immunoglobulins tell you?

Immunoglobulin levels can provide doctors with information about your health, such as if you have:

  • an infection
  • immunity to an illness
  • immunodeficiencies (your immune system is not working well)
  • certain allergies
  • autoimmune conditions (like types of arthritis, lupus, celiac disease, and other conditions)
  • certain cancers

Immunoglobulins are molecules plasma cells produce following B-cell activation due to exposure to a foreign agent. B-cells are a type of white blood cell.

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 a weakened immune system or symptoms of a condition associated with atypical antibody levels.