IgA deficiency is the most common primary immune deficiency, affecting roughly 1 in 500 to 700 people. It means your body produces little to no immunoglobulin A, a protective antibody that lines your respiratory and digestive tracts. Most people with IgA deficiency never develop serious problems, but some experience recurring infections, allergies, or autoimmune conditions that require ongoing management.
What IgA Does in Your Body
Immunoglobulin A (IgA) is your body’s frontline defense at mucosal surfaces, the wet linings inside your nose, throat, lungs, and gut. Unlike other parts of the immune system that fight infections by triggering inflammation, IgA works quietly. It coats bacteria, viruses, and other invaders before they can attach to or penetrate those surfaces, a process immunologists call “immune exclusion.” Think of it as a bouncer that turns away trouble at the door rather than starting a fight inside.
The IgA in your secretions has four or more binding sites, which makes it especially good at clumping microorganisms together. Once clumped, those invaders get swept away by the mucus in your airways or by the normal movement of your digestive tract. IgA also neutralizes bacterial toxins and enzymes, adding another layer of protection without causing the collateral damage that inflammation brings.
Why Many People Have No Symptoms
Here’s the part that surprises most people: the majority of those with IgA deficiency stay perfectly healthy. The reason is a backup system. When IgA is absent, your body typically ramps up production of secretory IgM, a different antibody that can partially fill the same role in mucosal surfaces. This substitution isn’t perfect, but it’s often enough to keep infections at bay. That’s why many people only discover their IgA deficiency incidentally, through blood work done for an unrelated reason.
How It’s Diagnosed
Selective IgA deficiency is diagnosed with a simple blood test that measures the concentration of IgA in your serum. The defining threshold is a serum IgA level below 0.07 g/L (or 7 mg/dL), with normal levels of the other major antibody classes (IgG and IgM). Most labs use a method called nephelometry, which can detect IgA down to about 0.05 to 0.1 g/L. Because IgA levels don’t fully mature until around age 4, the diagnosis is typically not confirmed in very young children.
Common Symptoms and Infections
When IgA deficiency does cause problems, the most frequent are recurring sinus and lung infections. The bacteria responsible tend to be the same ones that cause common ear infections and pneumonia in otherwise healthy people, but they come back more often and can be harder to shake. Over time, repeated lung infections can lead to bronchiectasis, a condition where the airways become permanently widened and scarred, making them even more vulnerable to future infections.
The gut is the other common trouble spot. Without adequate IgA, a parasitic infection called giardiasis becomes more likely. Giardia causes watery diarrhea, cramping, and bloating, and in IgA-deficient people it can be more persistent and harder to clear. Some people also develop small, harmless lumps of immune tissue in the small intestine as the body tries to compensate for the missing antibody.
IgA deficiency is also considered a risk factor for more severe COVID-19 infections, though the exact degree of increased risk is still being studied.
Links to Allergies and Autoimmune Disease
People with IgA deficiency are more prone to allergic conditions like asthma, eczema, and hay fever. Without IgA acting as a gatekeeper, more food proteins and environmental allergens slip through the gut and airway linings and into the bloodstream. This leads to elevated levels of immune complexes (antibodies bound to those stray proteins), which can trigger or worsen allergic responses.
The connection to autoimmune disease is especially notable with celiac disease. IgA deficiency occurs in 2 to 3% of people with celiac disease, which is 10 to 15 times higher than the rate in the general population. This overlap matters practically because the standard screening test for celiac disease relies on detecting IgA-based antibodies. If you’re IgA-deficient, that test will come back falsely negative. Your doctor needs to use an IgG-based celiac test instead. Other autoimmune conditions, including rheumatoid arthritis, lupus, and thyroid disease, also appear at higher rates in people with IgA deficiency.
The Blood Transfusion Risk
One of the most important things to know about IgA deficiency is a rare but serious complication involving blood transfusions. When someone who lacks IgA receives donated blood or plasma (which contains IgA), their immune system can recognize the IgA as foreign and produce antibodies against it. On a second exposure, those anti-IgA antibodies can trigger a severe allergic reaction, potentially including anaphylaxis. The reaction happens because immune cells loaded with these antibodies release histamine and other inflammatory chemicals when they encounter IgA again.
This doesn’t happen to everyone with IgA deficiency, but it’s serious enough that people who know they’re IgA-deficient should carry medical identification noting the condition. If a transfusion is ever needed, blood banks can provide IgA-depleted products or use blood from other IgA-deficient donors.
What Causes It
Most cases of IgA deficiency are genetic. The condition runs in families and is linked to variations in genes within the major histocompatibility complex, the same cluster of immune-system genes involved in many autoimmune diseases. A gene called TNFRSF13B, which helps regulate antibody-producing cells, has been specifically associated with IgA deficiency. The inheritance pattern isn’t simple, though. Multiple genes likely contribute, which is why severity varies so much even within the same family.
In some cases, IgA deficiency is secondary, meaning it’s caused by something else. Certain anti-seizure medications and immunosuppressive drugs can temporarily lower IgA production. When the medication is stopped, IgA levels sometimes recover.
How It’s Managed
There is no way to replace IgA directly. Unlike other immune deficiencies where patients receive regular infusions of antibodies (immunoglobulin replacement therapy), those infusions contain very little IgA and wouldn’t reach the mucosal surfaces where IgA is needed. Worse, giving IgA-containing products to someone with anti-IgA antibodies could trigger a dangerous reaction.
Instead, management focuses on treating infections promptly and aggressively when they occur. People with frequent sinus or lung infections may keep antibiotics on hand to start early at the first sign of illness. Monitoring for complications like bronchiectasis or autoimmune disease is part of long-term care. If allergies or asthma develop, those are treated with standard therapies.
For the subset of patients whose IgA deficiency coexists with low levels of IgG subclasses (a pattern that causes more frequent and severe infections), immunoglobulin replacement therapy may be considered, but with IgA-depleted products and careful monitoring for reactions.
Progression Over Time
IgA deficiency is generally a stable condition. Most people who are asymptomatic stay that way. A small percentage, estimated at around 5 to 10%, eventually progress to a more serious immune deficiency called common variable immunodeficiency (CVID), where IgG levels also drop and infections become significantly more frequent and severe. This is why periodic blood work to monitor immunoglobulin levels is worthwhile, particularly if infections seem to be getting worse or more frequent over time.