IgG (Immunoglobulin G) Biomarker Testing
An IgG test measures your most abundant antibody to assess immune function and past exposure, with easy ordering and Quest lab access via Vitals Vault.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
IgG (immunoglobulin G) is the most abundant antibody in your blood. Your IgG level gives a big-picture view of how much long-term antibody “coverage” your immune system is carrying at the moment.
An IgG test is not the same thing as an allergy test, and it is not designed to diagnose a specific infection by itself. Instead, it helps you and your clinician understand whether your immune system may be underproducing antibodies, overproducing them, or responding to ongoing inflammation.
Because IgG can shift with illness, medications, and chronic conditions, your result is most useful when it is interpreted alongside your symptoms, your medical history, and sometimes other immunoglobulins (IgA and IgM) or protein studies.
Do I need a IgG test?
You might consider an IgG test if you are dealing with frequent or unusually severe infections, especially sinus, ear, bronchial, or pneumonia-type infections that keep returning. Low IgG can be one clue that your body is not making or keeping enough protective antibodies.
This test can also be helpful when you have signs of chronic inflammation or immune activation, such as persistent fatigue, unexplained weight loss, prolonged fevers, swollen lymph nodes, or abnormal protein results on routine labs. High IgG is not a diagnosis by itself, but it can point toward a need for a more targeted workup.
You may also see IgG ordered when a clinician is evaluating immune deficiencies (including medication-related immune suppression) or monitoring certain autoimmune or inflammatory conditions. If you recently had an infection or vaccination, your clinician may time testing to avoid confusing short-term immune changes with a longer-term pattern.
Testing supports clinician-directed care and follow-up planning, but you should not use a single IgG number to self-diagnose or self-treat.
This is a CLIA-certified laboratory blood test; results should be interpreted in clinical context and are not a standalone diagnosis.
Lab testing
Ready to order an IgG test or bundle it with related immune labs?
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
If you want a clear starting point for immune system evaluation, you can order an IgG test through Vitals Vault and complete your blood draw at a participating lab location. Your report shows your measured IgG value and the lab’s reference interval so you can see where you land.
Because IgG is easiest to interpret with context, PocketMD can help you turn your result into next steps. For example, you can ask what follow-up tests are commonly paired with IgG (such as IgA, IgM, serum protein electrophoresis, or vaccine response testing) and what retest timing makes sense based on whether you were recently sick.
If your result is out of range, Vitals Vault makes it simple to reorder the same test for trending or to add companion labs so you and your clinician can confirm whether the pattern is persistent and clinically meaningful.
- Order online and complete your draw at a lab location
- Clear reference intervals and result flags on your report
- PocketMD guidance to prepare questions for your clinician
Key benefits of IgG testing
- Helps assess whether your immune system is producing an adequate amount of long-term antibodies.
- Supports evaluation of recurrent infections and possible antibody deficiency patterns.
- Provides a useful clue when total protein or globulin is abnormal on routine bloodwork.
- Can point toward chronic inflammation or immune activation when IgG is persistently elevated.
- Helps monitor immune effects of certain medications or conditions that suppress antibody production.
- Guides which companion tests may add clarity, such as IgA/IgM, SPEP, or light chains when appropriate.
- Makes it easier to trend immune status over time when you repeat testing under similar conditions.
What is IgG?
IgG (immunoglobulin G) is a class of antibody made by B cells and plasma cells. Antibodies are proteins that recognize targets such as viruses, bacteria, and other substances your immune system has learned to respond to.
IgG is often described as the “memory” antibody because it tends to rise after exposure and can remain present for a long time. That is why many infection- or vaccine-related tests measure pathogen-specific IgG (for example, rubella IgG immune status). A total IgG test is different: it measures the overall amount of IgG in your blood, regardless of what it is targeting.
Your IgG level is influenced by how much your body produces, how quickly IgG is broken down, and whether IgG is being lost (for example, through the kidneys or gastrointestinal tract). Because of that, an abnormal result is usually a prompt to look for the underlying reason rather than a final answer.
Total IgG vs pathogen-specific IgG
A total IgG test measures the combined concentration of all IgG antibodies in your blood. Pathogen-specific IgG tests measure IgG directed at one target (such as rubella), which is used to assess immunity or past exposure. It is possible to have a normal total IgG and still lack protective IgG to a specific vaccine-preventable disease, and it is also possible to have low total IgG that affects multiple types of protection.
Why clinicians pair IgG with other immune tests
IgG is one piece of the immunoglobulin picture. IgA is important for mucosal immunity (sinuses, lungs, gut), and IgM is often an early-response antibody. If IgG is abnormal, clinicians often look at IgA and IgM, your complete blood count (CBC), and sometimes protein studies to understand whether the issue is production, loss, or overproduction of antibodies.
What do my IgG results mean?
Low IgG levels
Low IgG can mean your body is not making enough antibodies, is losing antibodies, or is temporarily suppressed after illness or certain treatments. In real life, this often shows up as recurrent infections, infections that linger, or infections that become severe more easily than expected. Your clinician may look for patterns such as low IgA/IgM, medication effects (for example, immunosuppressants), kidney or gut protein loss, or an underlying immune deficiency. If your result is only mildly low, repeating the test when you are well can help confirm whether it is persistent.
IgG in the expected range
An in-range IgG level suggests your overall IgG antibody quantity is typical for the lab’s reference interval. This does not guarantee that every specific antibody response is strong, but it makes a major quantitative IgG deficiency less likely. If you still have frequent infections or immune concerns, your clinician may consider functional testing (such as vaccine response) or other immune markers rather than relying on total IgG alone.
High IgG levels
High IgG often reflects ongoing immune stimulation, which can happen with chronic infections, autoimmune or inflammatory conditions, and some liver diseases. Sometimes IgG is broadly elevated (polyclonal), and sometimes a single clone of antibody-producing cells is driving an increase, which is evaluated with additional protein studies when clinically indicated. A one-time elevation can occur after recent infection, so your clinician may recommend repeating the test and pairing it with other labs to determine whether the elevation is persistent and what pattern it follows.
Factors that influence IgG
Recent infections, vaccinations, and inflammatory flares can raise IgG temporarily. Medications that affect B cells or the immune system can lower IgG, and timing relative to treatment matters. Protein loss through the kidneys (proteinuria) or gut can lower IgG even if production is normal, so urine or protein studies may be relevant. Age, pregnancy status, hydration, and lab-to-lab reference intervals can also affect how your number should be interpreted.
What’s included
- Immunoglobulin G
Frequently Asked Questions
Do I need to fast for an IgG blood test?
Fasting is not usually required for a total IgG test. If you are ordering IgG alongside other labs that do require fasting (such as certain lipid tests), follow the instructions for the full set of tests on your order.
What is a normal IgG level?
“Normal” depends on the laboratory method and reference interval printed on your report, and ranges can vary by age. The most useful way to read your result is to compare it to the reference interval from the same lab and consider whether the value fits your symptoms and medical history.
What causes low IgG?
Low IgG can be caused by primary immune deficiencies, immune-suppressing medications or treatments, certain blood cancers, or protein loss through the kidneys or gastrointestinal tract. A recent severe illness can also temporarily lower immunoglobulins, which is why repeat testing is sometimes recommended.
What causes high IgG?
High IgG is commonly linked to chronic immune stimulation, such as autoimmune disease, chronic infection, or inflammatory liver conditions. In some cases, a more specific evaluation is needed to determine whether the elevation is broad (polyclonal) or driven by a single antibody clone.
Is IgG the same as an allergy test?
No. Most clinically validated allergy testing focuses on IgE, not total IgG. Some tests measure food-specific IgG, but that is a different use case than a total IgG level and is not the standard way to diagnose food allergy.
How is total IgG different from rubella IgG or other immunity tests?
Total IgG measures the overall amount of IgG antibody in your blood. Rubella IgG (and similar tests) measures IgG directed at one specific organism to estimate immunity or past exposure. You can have a normal total IgG and still be non-immune to a specific disease, depending on your vaccination or exposure history.
When should I retest IgG?
Retesting depends on why you tested in the first place. If you were recently sick or had a vaccine, your clinician may suggest waiting several weeks before repeating. If IgG is significantly low or high, follow-up testing is often done sooner and paired with related labs to confirm the pattern.