Normal IgG Levels by Age Chart: Understanding Reference Ranges and Results

Written By: Jillian Foglesong Stabile MD, FAAFP, DABOM

Immunoglobulins are antibodies in the body that play a role in the immune response. They make up about 20% of proteins in plasma. [1] There are five types of immunoglobulins: IgM, IgG, IgA, IgW, and IgD. IgG is the most common immunoglobulin present in the blood and makes up about 70-80% of immunoglobulins. [2] Immunoglobulin is responsible for the memory of the immune system and helps the immune system respond quickly in the case of exposure to a threatening substance.

Deficiencies in IgG can have significant impacts on the immune system and health. What are normal IgG levels and do they vary by age? This article will discuss the normal IgG levels by age.

Immunoglobulin G (IgG)

IgG, the most common immunoglobulin in the body, can be divided into four subclasses: IgG1, IgG2, IgG3, and IgG4. Each of these subclasses has a different role in the body despite their similarities. IgG1 and IgG3 are responsible for the body’s response to viruses and protein antigens. IgG2 is responsible for how the body responds to polysaccharide antigens, and IgG4 is responsible for how the body responds to certain types of roundworms, specifically nematodes. [3]

When the body is exposed to a substance that is a possible threat, plasma B cells produce IgG specific to that substance. When the body is exposed to the substance again, it binds it and makes it easier for the white blood cells to recognize and remove from the body. [4]

Key Notes:

• IgG1 and IgG3 are critical for fighting viral and protein-based pathogens due to their strong complement activation and high receptor affinity.
• IgG2 is essential for defense against encapsulated bacteria that polysaccharide antigens protect.
• IgG4 is associated with chronic antigen exposure, non-inflammatory immune responses, and allergen tolerance.

What Are Normal IgG Levels?

IgG antibodies are part of the secondary antibody response. This means that they exert the majority of their effects the second time you are exposed to the substance to which the IgG is responding. These antibodies remain in the body for a long time once they are created. [5] Secondary antibody responses are significantly stronger than primary antibody responses. [6]

Normal IgG levels can range from 6.0 to 16.0 in an adult. [7] IgG levels in children vary by age. IgG usually increases in childhood, reaching a peak in early adulthood, and then decreases with age. [8] IgG may also vary with health status.

What are Normal IgG Levels by Age

As previously mentioned, Immunoglobulin G reference ranges fluctuate with age. They generally increase from infancy to young adulthood and then decline with age. [8,11,12]

Infancy and Early Childhood:

"IgG levels are initially influenced by maternal antibodies transferred through the placenta, which protect the infant during the first few months of life. These antibodies decline around 6–9 months, and the infant’s immune system begins producing its own IgG."

Childhood and Adolescence:

"IgG levels increase steadily as the immune system matures, peaking during young adulthood when immune function is most robust."

Adulthood and Aging:

"In adults, IgG levels stabilize but may start to decline with age due to immunosenescence, the gradual weakening of the immune system. Older adults may show reduced IgG responses to new antigens, making vaccinations and immune monitoring important."

There are many reasons your healthcare provider may recommend testing your IgG levels.

Factors Affecting IgG Levels

The immune system is complex, and there are a number of factors that can affect it. In addition to your age, your IgG levels can be influenced by your genetics, your overall health status, and even your environment.

Probiotics are correlated with elevated IgG levels compared to baseline. [9] Fasting has been associated with lower IgG levels, though other dietary components are not associated with changes in immunoglobulin levels. Smoking and alcohol use are also associated with lower levels of IgG. [9]

Ethnic origin may correlate with IgG levels as well. A meta-analysis published in Frontiers in Immunology found that Caucasians have lower levels of IgG when compared to people of African, Asian, Amazonian, and Melanesian origin.[9]

Other conditions that can increase IgG levels include [10]:

• IgG myeloma
• Chronic liver disease
• Sarcoidosis
• Chronic infection
• Autoimmune disease
• Parasitic diseases

Conditions that lead to reduced IgG levels include [10]:

• Immunodeficiency (acquired or hereditary)
• Pregnancy
• Syndrome resulting in protein loss
• Waldenstrom’s macroglobulinemia
• Non-IgG myeloma

Abnormalities in IgG levels are generally non-specific, which means that the presence of abnormalities can't typically be used to diagnose a specific health condition. Abnormalities in these tests can serve as a reason for your healthcare provider to evaluate for other conditions.

Reasons for Testing IgG Levels

Abnormal IgG levels are associated with several different health conditions. Your healthcare provider may order this test to evaluate how your immune system is functioning in the case of recurrent infections or autoimmune disorders.[13]

IgG levels are most commonly ordered to evaluate for immune system deficiency, as low levels of IgG may result in certain abnormalities of the immune system. This can lead to recurrent infections and lung disease.[14]

Another reason that you may choose to have IgG levels checked is if you are concerned about food sensitivities. Food sensitivity testing looks for elevated levels of IgG in response to specific foods. An elevation in IgG may indicate that your body is sensing a specific food as a threat. This may result in GI discomfort or distress. [15] IgG-mediated food sensitivity testing can be used in combination with an elimination diet to determine whether specific foods are contributing to your symptoms. Symptoms of food sensitivity may include [15]:

• Gastrointestinal distress
• Medical Citation URL. Bloating
• Abdominal pain
• Gas
• Diarrhea
• Heartburn
• Nausea
• Headache
• Vomiting
• Joint pain
• Respiratory symptoms
• Brain fog

If you’re experiencing symptoms of food sensitivities, you may choose to get food sensitivity testing to try to narrow down what foods may be causing your distress.

Why it matters to test IgG levels at different ages:

Interpreting IgG Results

Once you have the results of your IgG testing, the next step is understanding IgG results. If you’re doing food testing for IgG, then the levels on your report are usually graded to the amount of IgG binding for each food.[16] Generally, these results suggest the amount of immune response to the individual foods. This may not necessarily correspond with the symptoms you are experiencing. A food sensitivity test is best used in combination with an elimination diet and reintroduction to determine if the foods identified are actually causing your symptoms.

IgG levels not specific to food sensitivity testing may be elevated or low. Low IgG levels are associated with immunologic conditions such as hypogammaglobulinemia, x-linked agammaglobulinemia, common variable immunodeficiency, ataxia-telangiectasia, severe combined immunodeficiency, and Good’s syndrome, among others. [17] They may also be low in relation to medication, such as those that suppress the immune system, treat seizures, or treat cancer. Nephrotic syndrome and other conditions that cause protein loss, cancers, and HIV can all cause low IgG levels as well. [18]

High IgG levels are much less common but can be associated with autoimmune conditions, some cancers, chronic infections or inflammation, and pelvic inflammatory disease (PID). Chronic liver disease and some parasitic diseases can also cause IgG levels to be elevated. [10]

If IgG levels are abnormal, it’s a sign that additional testing may be indicated as abnormalities in IgG levels alone are not sufficient to diagnose the conditions that can contribute to the abnormalities. To determine the cause of the abnormalities, you should consult with your healthcare provider to determine what other testing might be indicated because each of the conditions has specific recommended testing as well as specific symptoms.

Low IgG Levels

Low IgG levels, known as hypogammaglobulinemia, may indicate a weakened immune system, making the individual more susceptible to infections. The underlying causes of low IgG can vary by age and condition:

In Infants and Children:

Persistent low IgG levels may suggest congenital immunodeficiencies, such as:

• Severe Combined Immunodeficiency (SCID)
• Common Variable Immunodeficiency (CVID)
• X-linked Agammaglobulinemia (XLA)

These conditions often present with recurrent infections, failure to thrive, or chronic respiratory issues.

In Adults:

Acquired causes of low IgG include:

• Immunosuppressive therapies (e.g., chemotherapy, corticosteroids)
• Nephrotic syndrome or protein-losing enteropathy, where proteins are lost excessively.
• HIV or other chronic infections that impair immune function.

During Pregnancy:

Physiological changes can lead to reduced IgG levels, though these typically normalize post-pregnancy.

Implication: Low IgG levels necessitate further testing, such as subclass analysis, T-cell and B-cell counts, or genetic testing, to identify the specific cause and guide treatment.

High IgG Levels

Elevated IgG levels, while less common, can be associated with overactive immune responses or chronic conditions:

Chronic Infections:

Persistent infections, such as tuberculosis or viral hepatitis, can stimulate IgG production.

Autoimmune Diseases:

Conditions like lupus, rheumatoid arthritis, and multiple sclerosis often result in elevated IgG levels due to chronic inflammation.

Cancers:

Certain blood cancers, including multiple myeloma and IgG myeloma, can cause significantly high IgG levels.

Parasitic Diseases:

Chronic parasitic infections (e.g., caused by nematodes) may lead to localized or systemic IgG elevation.

Implication: High IgG levels should prompt further investigation, including imaging studies, bone marrow analysis, or specific infection panels, to confirm the underlying cause.

Normal IgG Levels

Normal IgG levels vary with age and are a strong indicator of a well-functioning immune system. However, symptoms like recurrent infections or chronic inflammation may still necessitate further testing to rule out conditions not directly affecting IgG levels.

Understanding Subclass Results

IgG testing often includes subclass analysis (IgG1, IgG2, IgG3, IgG4) to refine the diagnosis:

• IgG1 and IgG3 Deficiencies: Common in viral and protein antigen responses.
• IgG2 Deficiency: Associated with recurrent bacterial infections, especially involving encapsulated bacteria.
• IgG4 Deficiency: Rare but linked to specific autoimmune or allergic conditions.

Learn More About Your Health With Everlywell

Your health matters. When you have concerns about your health, it can be difficult to find the time to get in with a healthcare provider. Taking time out of your busy life to sit around a doctor’s office and wait can be inconvenient. At Everlywell, we offer a range of at-home testing and virtual consultations that bring the visit to you.

If you’re concerned about food sensitivities, consider using an at-home Food Sensitivity Test from Everlywell, which can be used to evaluate your body’s IgG response to 96 common foods. For even more information, you can take the Food Sensitivity Comprehensive Test, which evaluates your IgG levels in response to 204 foods. If you have questions about the next step for managing food sensitivity or other health concerns, you can schedule an online visit with one of our certified healthcare professionals.

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