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

Immunoglobulin G (IgG) reference ranges naturally fluctuate throughout life. IgG levels generally increase from infancy through young adulthood before gradually declining with age.[8,11,12]

Age Range	Typical IgG Level (g/L)
<2 weeks	5.0–17.0
2–4 weeks	3.9–13.0
1–3 months	2.1–7.7
3–6 months	2.4–8.8
6–9 months	3.0–9.0
9–12 months	3.0–10.9
1–2 years	3.1–13.8
2–3 years	3.7–15.8
3–6 years	4.9–16.1
6–15 years	5.4–16.1
16–45 years	6.0–16.0
Over 45 years	6.0–16.0

IgG Levels During Infancy and Early Childhood

In infancy, IgG levels are heavily influenced by maternal antibodies transferred through the placenta during pregnancy. These antibodies help protect newborns during the first few months of life. Around 6–9 months of age, maternal antibodies begin to decline, and the infant’s immune system gradually starts producing its own IgG antibodies.

IgG Levels During Childhood and Adolescence

As children grow, IgG levels steadily increase alongside immune system development. IgG production typically reaches its peak during young adulthood, when immune function is generally strongest.

IgG Levels in Adulthood and Aging

In adulthood, IgG levels tend to stabilize but may gradually decline later in life due to immunosenescence, the natural aging of the immune system. Older adults may have reduced immune responses to new antigens, which is one reason vaccinations and immune health monitoring can become increasingly important with age.

There are many reasons a healthcare provider may recommend testing IgG levels, including evaluating immune function, investigating recurrent infections, or assessing responses related to certain health conditions.

IgG is the most abundant immunoglobulin in the body and plays an important role in immune system function. There are four subclasses of IgG antibodies—IgG1, IgG2, IgG3, and IgG4—each with distinct immune responsibilities. While these subclasses share structural similarities, they respond to different types of antigens and immune challenges.[3]

When the immune system encounters a substance it identifies as potentially harmful, plasma B cells produce IgG antibodies specific to that substance. Upon future exposure, these antibodies help the immune system recognize and respond to the substance more efficiently by supporting white blood cells in identifying and removing it from the body.[4]

IgG Subclass	Primary Function	Percentage of Total IgG	Key Characteristics
IgG1	Responds to protein antigens such as viruses and bacterial toxins	60–70%	Most abundant IgG subclass and critical for immune defense against viruses and protein-based pathogens
IgG2	Responds to polysaccharide antigens, including bacterial capsules	20–25%	Important for protecting against encapsulated bacteria such as Streptococcus pneumoniae and Haemophilus influenzae
IgG3	Supports strong immune responses to viruses and protein antigens	5–8%	Efficiently activates the complement system and has a high affinity for Fc receptors, though it has a shorter half-life than IgG1
IgG4	Associated with repeated or long-term antigen exposure, including allergens and certain parasites	1–4%	Typically non-inflammatory and linked to immune tolerance, such as in allergen desensitization therapies

Key Takeaways About IgG Subclasses

• IgG1 and IgG3 are especially important for defending the body against viruses and other protein-based pathogens.
• IgG2 helps protect against bacteria with polysaccharide coatings that can evade other immune responses.
• IgG4 is commonly associated with long-term antigen exposure and immune tolerance rather than inflammatory reactions.

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.

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:

How to Interpret IgG Test Results

Once you receive your IgG test results, the next step is understanding what the results may mean. In food sensitivity testing, IgG levels are typically graded based on the amount of IgG antibody binding detected for each food.[16]

• Higher IgG reactivity may indicate a stronger immune response to a specific food.
• Lower IgG reactivity may indicate less immune recognition of that food.
• Results do not always directly correlate with symptoms.
• Food sensitivity testing is often most useful when combined with an elimination diet and structured food reintroduction.

Because symptoms and immune responses can vary from person to person, working with a healthcare provider can help you determine whether identified foods may be contributing to your symptoms.

What Low IgG Levels May Indicate

Low IgG levels may be associated with certain immune-related conditions or other underlying health concerns.[17][18]

• Hypogammaglobulinemia
• X-linked agammaglobulinemia
• Common variable immunodeficiency (CVID)
• Ataxia-telangiectasia
• Severe combined immunodeficiency (SCID)
• Good’s syndrome

Low IgG levels may also occur due to:

• Immune-suppressing medications
• Certain seizure medications
• Cancer treatments
• Nephrotic syndrome or protein-losing conditions
• HIV infection
• Certain cancers

What High IgG Levels May Indicate

Elevated IgG levels are less common but may be associated with several inflammatory or chronic conditions.[10]

• Autoimmune disorders
• Chronic infections
• Inflammation
• Pelvic inflammatory disease (PID)
• Chronic liver disease
• Certain parasitic infections
• Some cancers

When to Follow Up With a Healthcare Provider

Abnormal IgG levels alone are not enough to diagnose a specific condition. If your results fall outside the normal range, additional testing may be needed to identify the underlying cause. Because many different conditions can affect IgG levels, your healthcare provider can help determine which follow-up tests or evaluations may be appropriate based on your symptoms, medical history, and overall health.

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.

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.