What Is a Normal IgA Level? High vs. Low Levels Explained

A normal serum IgA level in adults generally falls between about 70 and 400 mg/dL, though the exact range varies depending on the laboratory, the testing method used, and the patient’s age. IgA is the second most abundant antibody in the bloodstream and the dominant one in mucosal secretions like saliva, tears, and the lining of the gut. Because IgA levels shift dramatically from birth through adulthood, a “normal” number for a two-year-old looks nothing like a normal number for a thirty-year-old, and understanding why a result is high or low matters more than the number alone.

What IgA Actually Does

IgA comes in two main forms. In the blood, it circulates mostly as a single unit (a monomer) and helps neutralize pathogens that have made it into the bloodstream. In mucosal surfaces, it exists primarily as a dimer, two units joined together and wrapped in a protective protein coat that keeps it from being digested. This secretory form, often called SIgA, is the body’s first line of antigen-specific defense at surfaces exposed to the outside world: the gut, the airways, the urinary tract, and the eyes.¹

In the intestine, SIgA does something more nuanced than simply killing invaders. It coats bacteria, both harmful ones and the beneficial microbes that make up the gut microbiota, to regulate where they can live and how they interact with the intestinal lining. This “immune exclusion” prevents pathogens from sticking to and crossing the gut wall while allowing commensal microbes to continue their metabolic work undisturbed.² The relationship is reciprocal: products released by gut microbes stimulate the body to make more SIgA, which in turn shapes the microbial community. When that cycle is disrupted, the risk of infections and inflammatory diseases of the intestine goes up.³

Breast milk is loaded with SIgA for exactly this reason. Newborns cannot produce meaningful amounts of their own IgA, so maternal antibodies coat the infant’s gut and provide protection until the baby’s immune system begins manufacturing IgA independently.³

How IgA Levels Change with Age

IgA levels at birth are extremely low. Newborns have almost none in their blood, and production ramps up gradually throughout childhood and adolescence. Studies tracking pediatric reference ranges show that IgA concentrations climb steadily and do not peak until around age 18.⁴ Boys and girls appear to increase their IgA at similar rates; sex differences have not been demonstrated in pediatric populations.⁵

This slow maturation is why low IgA in a toddler does not automatically signal a problem. Some young children have what is called transient hypogammaglobulinemia of infancy, a temporary delay in reaching normal immunoglobulin levels. In most cases, levels catch up before age three or four, though a small number of children still have low IgA or IgG beyond that point and may need follow-up.⁶ The condition is generally considered a normal variant of immune development rather than a true immunodeficiency.⁷

Because of this steep age-related trajectory, pediatric labs typically report IgA results against age-specific reference intervals. Comparing a child’s level to an adult range would make nearly every young child look deficient. If your child’s lab report uses adult norms and the number looks alarmingly low, ask whether age-appropriate ranges were applied before worrying.

What High IgA Can Mean

An elevated serum IgA is not a diagnosis by itself. It is a signal that the immune system is responding to something, and the clinical context determines how much it matters. Mildly elevated IgA shows up during ordinary infections and usually returns to baseline once the infection resolves. Persistently high IgA, though, points to a shorter list of possibilities worth investigating.

Liver Disease

Chronic liver disease is one of the more common reasons for a high IgA level. Serum IgA rises in patients with alcoholic liver disease, and research on non-alcoholic fatty liver disease shows a similar pattern: IgA levels climb as liver fibrosis becomes more severe, with the highest values seen in advanced scarring.⁸ In chronic hepatitis B, IgA has been identified as an independent predictor of cirrhosis, with levels rising further in decompensated cirrhosis compared with compensated disease.⁹ The mechanism probably involves the liver’s central role in clearing IgA from the blood; when the liver is damaged, IgA accumulates.

IgA Nephropathy

IgA nephropathy is the most common form of glomerulonephritis worldwide, and it occurs when abnormally shaped IgA1 molecules deposit in the kidneys’ filtering units. Patients with this disease tend to have elevated levels of a specific form of IgA1 that lacks certain sugar molecules (called galactose-deficient IgA1). A blood test measuring this abnormal IgA1 identified about three-quarters of patients in one study, with a specificity around 94%.¹⁰ Diagnosis still typically requires a kidney biopsy, but research into biomarkers based on these abnormal IgA1 molecules continues, and they may eventually serve as a less invasive screening tool.¹¹

Other Causes

Beyond liver and kidney disease, high IgA can show up in chronic infections, certain autoimmune conditions, and IgA-producing blood cancers such as IgA multiple myeloma. A one-time elevated reading without symptoms is often rechecked before further workup, because even stress and recent illness can push the number up temporarily.

What Low IgA Can Mean

Low IgA is more common than most people realize, and in many cases it causes no symptoms at all. The most frequent scenario is selective IgA deficiency, defined as a serum IgA below 7 mg/dL (sometimes reported as below 5 mg/dL depending on the lab) with normal levels of IgG and IgM. It is the most common primary immunodeficiency, and its prevalence varies strikingly by ethnicity, roughly one in 500 people of European ancestry have it.¹² Genetically, it appears to involve common variants rather than rare, high-impact mutations, which makes it different from many other inborn immune errors.¹³

Many people with selective IgA deficiency live their entire lives without knowing they have it. Others develop recurring sinus and lung infections, gut infections (with a particular susceptibility to the parasite Giardia), or allergic conditions.¹⁴ The more clinically significant association, though, is with autoimmune disease.

The Link Between IgA Deficiency and Autoimmunity

A population-based matched cohort study found that people with IgA deficiency had a 35-fold higher rate of celiac disease compared with controls, along with a roughly 10-fold higher rate of type 1 diabetes. Elevated rates also appeared for inflammatory bowel disease (about five times higher), rheumatoid arthritis (about four and a half times higher), and thyroid disorders (about four times higher).¹⁵ These associations have been confirmed across multiple populations and reviews.¹⁶

The direction of causality is not fully settled. The shared genetic architecture between IgA deficiency and autoimmune diseases suggests both may stem from common immune-regulatory pathways rather than one directly causing the other. Regardless of the mechanism, a diagnosis of selective IgA deficiency is a reason to stay alert for autoimmune symptoms, especially gastrointestinal complaints that might point to celiac disease.

Drug-Induced Low IgA

Certain medications can suppress IgA production. The best-documented example is phenytoin and other older anticonvulsant drugs. Research has shown that a significant fraction of patients taking anticonvulsants develop IgA levels below the normal floor, with the effect sometimes appearing within two to three months of starting treatment. In one study, roughly a fifth of adult patients and over 40% of children on anticonvulsants had abnormally low IgA, while epileptic patients not on medication had normal levels.¹⁷ If you are on anticonvulsant therapy and a blood test shows low IgA, the medication is a likely explanation, but it is still worth discussing with your doctor to rule out other causes.

Why Low IgA Complicates Celiac Disease Testing

This is one of the most practical consequences of IgA deficiency, and it catches both patients and clinicians off guard. The standard blood test for celiac disease looks for IgA antibodies against tissue transglutaminase (tTG-IgA). If you cannot make IgA in the first place, you will test negative for those antibodies even if you have full-blown celiac disease.¹⁸ This false-negative problem is well documented.¹⁹

The workaround is to measure total IgA alongside celiac-specific antibodies. If the total IgA is very low, the lab or clinician should switch to IgG-based celiac antibody tests instead. IgG antibodies against tissue transglutaminase appear to be more reliable in IgA-deficient adults than some alternatives.²⁰ Given that IgA deficiency and celiac disease overlap so heavily, failing to check total IgA when screening for celiac is a meaningful gap. If you have been told your celiac screen was negative but you have ongoing gut symptoms, it is worth asking whether your total IgA was measured at the same time.

Transfusion Reactions in IgA-Deficient People

A less common but serious concern for people with very low or absent IgA is the risk of anaphylactic transfusion reactions. When someone who completely lacks IgA develops anti-IgA antibodies, receiving blood products that contain IgA can trigger a severe allergic response. These reactions are rare, estimated at roughly one in 20,000 to 47,000 transfusions.²¹ The typical presentation includes chest pain, difficulty breathing, and severe drop in blood pressure without blood loss, a pattern distinct from other transfusion reactions.²²

Not every IgA-deficient person develops these antibodies. In one large study using a hemagglutination assay, about 76% of IgA-deficient patients who had experienced an anaphylactic transfusion reaction tested positive for anti-IgA, compared with about 22% of IgA-deficient blood donors who had never had a reaction.²³ For patients known to have anti-IgA antibodies, blood banks can provide IgA-deficient blood products to prevent future reactions. If you know you are IgA-deficient, it is worth making sure that is noted in your medical record before any surgery or situation where transfusion might be needed.

Exercise and Salivary IgA

Athletes and coaches sometimes hear that heavy training suppresses IgA and raises infection risk. There is some truth to this, but the picture is more specific than the headline suggests. What is actually measured in most exercise-immunology studies is salivary IgA (the secretory form in your mouth), not serum IgA from a blood draw. And the effect depends heavily on how hard and how long you exercise.

A controlled experiment found that high-intensity exercise (at about 75% of maximal oxygen uptake) caused salivary IgA secretion rates to drop by roughly 46% immediately after the session compared with moderate-intensity exercise. Cortisol, a stress hormone, rose sharply during the harder workout, and its increase correlated with the drop in salivary flow. Separately, exercising for 90 minutes produced a larger IgA drop than a 30-minute session at the same intensity.²⁴ The practical implication for endurance athletes is real: extended, high-intensity sessions temporarily reduce oral mucosal defenses, which may partly explain the increase in upper respiratory infections during heavy training blocks. Moderate exercise does not appear to carry the same risk.

Salivary IgA tests are not part of routine clinical workups, but they occasionally appear in sports-medicine and occupational-health settings. A low salivary IgA reading after a marathon does not mean you have an immune deficiency; it means your mucosal defenses are temporarily depleted and you should take basic precautions like avoiding crowded, enclosed spaces in the hours after a hard effort.

Management When IgA Is Abnormal

For high IgA, there is no treatment aimed at lowering IgA itself. The goal is to address whatever is driving the elevation, whether that is liver disease, IgA nephropathy, a chronic infection, or an IgA-producing malignancy. The IgA level then becomes one metric among many used to track how the underlying condition is progressing.

For low IgA, management depends on symptoms. Many people with selective IgA deficiency need nothing beyond awareness of their status. Those who develop frequent infections, especially of the sinuses and lungs, may benefit from prompt antibiotic treatment when infections occur and in some cases prophylactic antibiotics during infection-prone seasons. IgG replacement therapy, the standard treatment for more severe antibody deficiencies, is not routinely given for isolated IgA deficiency because most patients have normal IgG and IgM that compensate. Clinical guidelines recommend reserving immunoglobulin replacement for patients who also have deficient IgG subclasses or who experience infections that do not respond to standard management.²⁵

Vaccinations remain effective for people with selective IgA deficiency because their IgG and IgM responses are intact. There is no need to avoid vaccines, and staying current on immunizations is a good idea given the slightly increased susceptibility to respiratory infections.

The Evolutionary Roots of IgA

IgA is not unique to humans or even to mammals, though its molecular form has changed over evolutionary time. Research comparing antibody molecules across vertebrates suggests that IgA evolved from an older immunoglobulin class called IgY, which is still found in birds, reptiles, and amphibians. Cross-reactivity studies show close antigenic relationships between mammalian IgA and the IgY found in chickens and other non-mammalian vertebrates, leading researchers to place IgY as the ancestral precursor.²⁶

The gene duplication event that separated IgA from IgG and IgE appears to have happened very early in mammalian evolution. Marsupials, which split from placental mammals well over 100 million years ago, already carry distinct IgA, IgG, and IgE genes. Cloning of these genes from the grey short-tailed opossum confirmed that all three isotypes were present and structurally similar to their counterparts in placental mammals, even though opossum versions sit on clearly separate branches of the phylogenetic tree.²⁷ The fact that IgA’s specialized mucosal role was already established before marsupials and placental mammals diverged hints at how fundamental this antibody class has been to mammalian survival, particularly at body surfaces where constant microbial contact demands a nuanced, non-inflammatory immune response.