Overview
Immunoglobulin G (IgG) is the most common and abundant antibody in the human body. Around 75–80% of all antibodies in the bloodstream are IgG. Because of its high presence and long lifespan, IgG is one of the most important antibodies for fighting infections and providing long-term immunity.
IgG is produced when the body encounters bacteria, viruses, fungi, or foreign substances known as antigens. Once produced, IgG circulates throughout the blood, tissues, and lymphatic system, helping to neutralize harmful invaders. This antibody is also responsible for long-term protection after vaccinations or past infections.
Doctors commonly order an IgG blood test to evaluate the immune system, diagnose infections, check for antibody deficiencies, and monitor autoimmune or chronic inflammatory diseases.
Where Is IgG Produced in the Body?
IgG is produced by plasma cells, a type of white blood cell formed from B lymphocytes. The production mainly occurs in:
- Bone marrow
- Lymph nodes
- Spleen
- Mucosal tissues (respiratory & gastrointestinal)
Once produced, IgG is released into:
- Bloodstream
- Body tissues
- Lymphatic system
IgG can also move across cell barriers, allowing it to travel to different organs. One special feature of IgG is its ability to cross the placenta, providing newborn babies with immunity for the first few months of life.
Main Functions and Importance of IgG
IgG has several crucial functions:
1. Provides long-term immunity
After an infection or vaccination, IgG remains in the body for years, sometimes for life. This helps prevent reinfection.
2. Neutralizes harmful microbes
IgG attaches to viruses, bacteria, and toxins to block their activity.
3. Activates the complement system
IgG triggers a series of reactions that help destroy microbes.
4. Enhances phagocytosis
It marks harmful organisms so immune cells can swallow (engulf) and kill them—called opsonization.
5. Protects unborn babies
IgG crosses the placenta from the mother to the fetus, giving the baby temporary immunity after birth.
Because of these essential roles, IgG tests are commonly used to assess how strong a person’s immune system is.
Causes of Low IgG Levels
Low IgG levels indicate a problem with the body’s immune system. Common causes include:
1. Primary Immunodeficiency Disorders
Example: Common Variable Immunodeficiency (CVID) — a chronic condition where the body cannot produce enough antibodies.
2. Genetic Disorders
Some inherited conditions prevent proper antibody formation.
3. Cancers of Blood Cells
Conditions like Chronic Lymphocytic Leukemia (CLL) or lymphoma reduce IgG production.
4. Medical Treatments
- Chemotherapy
- Radiation therapy
- Immunosuppressive drugs
These treatments can damage cells that produce antibodies.
5. Protein-Loss Conditions
IgG can be lost through:
- Nephrotic syndrome (kidney disease)
- Severe burns
- Gastrointestinal protein loss
Symptoms of Low IgG Levels
People with low IgG often experience:
- Frequent or repeated infections
- Sinus infections
- Ear infections
- Lung infections (bronchitis, pneumonia)
- Urinary tract infections
- Poor response to vaccines
- Slow or delayed healing
- Recurrent fever or severe bacterial infections
Low IgG makes the body more prone to both common and serious infections.
Causes of High IgG Levels
High IgG levels usually indicate long-term inflammation, autoimmune disease, or chronic infection.
1. Chronic Infections
Examples:
- Tuberculosis
- HIV
- Long-standing bacterial infections
2. Autoimmune Diseases
IgG rises when the immune system mistakenly attacks the body:
- Lupus (SLE)
- Rheumatoid arthritis
- Autoimmune hepatitis
3. Liver Diseases
The liver plays a role in IgG metabolism. Conditions causing high IgG include:
- Cirrhosis
- Chronic hepatitis
4. Blood Cancers
Some cancers cause one type of IgG to become extremely elevated:
- Multiple myeloma
- Monoclonal gammopathy
5. Chronic Inflammation
Any long-standing inflammatory condition can increase IgG levels.
Symptoms of High IgG Levels
High IgG itself does NOT cause symptoms.
Symptoms come from the underlying disease.
Common signs include:
Autoimmune Disease Symptoms
- Joint pain
- Fatigue
- Skin rashes
- Muscle aches
Liver Disease Symptoms
- Jaundice
- Abdominal swelling
- Weakness
- Loss of appetite
Multiple Myeloma Symptoms
- Bone pain
- Frequent infections
- Anemia
- Kidney problems
Reference Ranges
Reference range varies slightly by lab, age, and testing method.
Adults
700 – 1600 mg/dL
Children
Lower in newborns and infants; gradually increases with age.
Abnormal values must always be interpreted with symptoms and medical history.
Sample Type
The sample needed for IgG testing is:
- Blood sample (serum or plasma) taken from a vein.
In some cases, doctors may also order tests for IgG subclasses (IgG1, IgG2, IgG3, IgG4).
Test Preparation
No special preparation is required.
- You do NOT need to fast
- Take regular medications unless advised otherwise
- Inform your doctor if you are on immunosuppressants
- Tell your doctor if you have frequent infections or autoimmune conditions
When to Consult a Doctor
See a doctor if you experience:
- Repeated infections
- Chronic sinus or chest infections
- Unexplained fatigue
- Autoimmune symptoms
- Symptoms of liver disease
- Poor vaccine response
- Delayed recovery from infections
- Child with frequent infections or poor growth
Doctors may order IgG along with IgA and IgM for a full immune evaluation.
Important Word Explanations
- Antibody: A protein that helps fight infections.
- Antigen: A foreign substance like a virus or bacteria.
- Plasma cells: White blood cells that produce antibodies.
- Complement system: A group of proteins that help kill microbes.
- Immunodeficiency: When the immune system is weak.
- Opsonization: Marking germs so immune cells can destroy them.
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