IgG4 blood test: What high IgG4 levels mean

Getting bloodwork done for any reason can be nerve-wracking. What do the results mean? Do they point to a specific health problem? For IgG4-related disease (IgG4-RD), a condition marked by swelling and inflammation that can affect multiple organs, an IgG4 blood test can offer some insight, but the results aren’t always straightforward.

Understanding what high IgG4 levels mean — and what they don’t — can help you interpret your lab results with proper context.

What is an IgG4 blood test?

An IgG4 blood test measures the amount of immunoglobulin G4 (IgG4) antibodies present in your blood.

IgG4 is one of four types of IgG antibodies. Antibodies are proteins made by the immune system to help your body recognize and neutralize foreign invaders.

The exact role IgG4 plays in the body isn’t totally clear. However, scientists think that it can help calm immune reactions and promote tolerance to certain foods or environmental allergens.

IgG4 is normally present in small amounts, making up fewer than 5% of total IgG antibodies in a healthy person. When doctors order this test, they’re usually looking for signs that the immune system may be overactive or reacting in an unusual way.

What can cause high IgG4 levels?

One potential cause of elevated IgG4 serum levels is IgG4-RD. People living with this condition often have increased levels because large numbers of IgG4-producing cells and other immune cells build up in affected tissues.

However, IgG4-RD is just one possible cause. Several other unrelated conditions can also lead to increased IgG4 levels. These include allergic diseases, chronic infections, and certain autoimmune disorders. Certain inflammatory diseases and cancers can also cause IgG4 to increase.

Because several conditions can cause high IgG4 levels, doctors rarely rely on this result alone when making an IgG4-RD diagnosis.

Can you have IgG4-RD with normal IgG4 levels?

Some people with IgG4-RD have normal IgG4 blood levels. Recent studies suggest that about 10% to 30% of patients have IgG4 serum levels within the normal range, even though they meet criteria for the disease based on tissue analysis.

Other studies report even higher rates. In one study of 125 patients with IgG4-RD, about 49% of those with active disease had normal IgG4 levels in their blood.

This means that a normal IgG4 blood test doesn’t necessarily rule out the condition. Doctors consider many factors to establish a diagnosis, including symptoms, imaging, and biopsy findings.

Why doctors do not diagnose IgG4-RD from bloodwork alone

Blood tests can offer important clues, but they don’t paint the full picture. IgG4-RD blood tests can measure antibody levels in the bloodstream, as well as blood levels of inflammatory molecules and immune cells that are sometimes changed in people with IgG4-RD.

But these markers are not specific to IgG4-RD. Other signs of the disease, such as the presence of swelling or masses in commonly affected organs, or patterns suggestive of IgG4-RD in tissue samples, are needed to establish a diagnosis.

Which tests may come next?

If your bloodwork shows abnormal IgG4 levels, your doctor may want to order further testing to better understand what’s going on. Common next steps may include:

• Imaging scans, such as CT or MRI: These can reveal masses, areas of damage, or enlarged organs.
• Biopsy: A small tissue sample may be taken from an affected part of the body to look for immune cell buildup and high numbers of IgG4-producing cells.
• Additional blood tests: These can help rule out other conditions that can mimic IgG4-RD.

Questions to ask your doctor

If you’re still unclear on how to interpret your lab results, that’s normal. Your doctor knows your situation best and can help you better understand your results and what comes next. At your next appointment, you might consider asking:

• What do my IgG4 serum levels mean for my situation?
• Could another condition explain these results?
• What other tests might I need next?

Don’t be afraid to ask follow-up questions if you don’t understand something. Clear answers can help you navigate the diagnostic and treatment process with confidence.