IgA Test

Immunoglobulin A (IgA) is a type of antibody, one of the key proteins your immune system uses to recognize and neutralize threats like bacteria, viruses, and other pathogens. What makes IgA special is where it operates: rather than circulating deep in your bloodstream like some other immune proteins, most of the IgA in your body lives at the edges, lining the moist surfaces of your mouth, lungs, gut, and genitals. These surfaces, known collectively as mucous membranes, are the body’s front line. IgA acts like a quiet bouncer, preventing invaders from sticking around long enough to cause real trouble.

There are two main forms of IgA: serum IgA, which is found in your blood, and secretory IgA, which is found in places like saliva, breast milk, and the lining of your intestines. The form detected on a typical blood test is serum IgA. While it only makes up a fraction of the total IgA in your body, changes in serum IgA can still offer important insights into how your immune system is functioning or misfiring.

Serum IgA doesn’t usually trigger inflammation. It binds to specialized receptors (called FcαRI or CD89) on immune cells like monocytes and neutrophils, helping to clear out pathogens and immune complexes in a quiet, non-inflammatory way. This unique ability allows it to play a kind of peacekeeping role: clearing infections or immune triggers without launching a full-blown inflammatory response.

Secretory IgA, on the other hand, is often found in dimeric form, two IgA units joined together with a special “J chain” protein. This version of IgA is especially good at neutralizing bacteria and viruses at the surface level before they even enter the bloodstream. It’s also resistant to enzymes and acids in the gut and respiratory tract, making it particularly resilient in hostile environments. This protective barrier function is crucial for maintaining a peaceful relationship between your immune system and the trillions of microbes that live on and in you.

This balancing act is important. Too little IgA, and your mucosal surfaces become vulnerable to infection and inflammation. Too much, or the wrong form, can contribute to problems like autoimmune conditions or kidney damage.

When IgA Goes Off Track

Low IgA levels can suggest a condition called Selective IgA Deficiency, the most common primary immunodeficiency. People with this condition often have few or no symptoms, but some may experience more frequent sinus infections, bronchitis, or gastrointestinal issues like chronic diarrhea or food sensitivities. Interestingly, many people with low IgA don’t get sick more often; thanks to backup systems like secretory IgM, which can perform many of the same functions.

In more serious immune disorders, like Common Variable Immunodeficiency (CVID) or ataxia-telangiectasia, IgA levels can also be low. In these cases, the deficiency is usually part of a broader immune dysfunction and may come with more significant clinical symptoms.

Elevated IgA levels are often a clue that your immune system is reacting to something. High IgA levels can be seen in chronic infections, autoimmune conditions (like lupus or rheumatoid arthritis), liver disease (including alcoholic cirrhosis), and certain cancers like IgA myeloma, a rare blood cell cancer. But one of the most important and specific connections is with IgA nephropathy, a kidney condition.

IgA nephropathy, also known as Berger’s disease, occurs when IgA deposits build up in the tiny filtering units of the kidneys. These deposits trigger inflammation that can eventually damage kidney function. Not all patients with IgA nephropathy have high IgA levels in their blood—but many do. Researchers have found that the IgA in this disease often has a distinctive pattern of sugar attachments (known as aberrant glycosylation), which makes it more likely to trigger immune responses and deposit in the kidneys.

Interestingly, not all elevations in IgA are bad. For example, salivary IgA often rises during short-term stress, acting as a quick-response marker for immune readiness. Some researchers are studying it as a potential tool for tracking how the body responds to psychological or physical stress, particularly in children and athletes.