An immunoglobulin A (IgA) test measures the level of IgA antibodies in your blood, and sometimes in your saliva. It’s used to help diagnose immune deficiencies, celiac disease, kidney disease, liver disease, and certain blood cancers. Your body produces more IgA than any other type of antibody, and it serves as the primary defense along the lining of your gut, lungs, and sinuses, so abnormal levels can point to problems in any of those areas.
What IgA Does in Your Body
IgA is the dominant antibody on every moist surface inside your body: the intestines, airways, sinuses, and throat. While IgG runs the show in your bloodstream, IgA patrols the mucosal barriers where you’re most exposed to the outside world. It works in two modes. In one, it binds tightly to specific threats like toxins and infectious microbes to neutralize them. In the other, it operates at lower intensity to keep the trillions of normal gut bacteria contained in the intestinal space where they belong.
Because IgA is concentrated in these barrier tissues, a deficiency often shows up as recurring infections in the sinuses, throat, ears, and lungs, or as chronic diarrhea and gut infections. That’s typically the pattern that prompts a doctor to order the test.
Why Your Doctor Might Order This Test
The most common reason is a pattern of repeated infections, particularly ones that keep coming back in the same location. Recurrent strep throat, chronic sinus infections, repeated bouts of pneumonia or bronchitis, and persistent gastrointestinal infections all raise suspicion of low IgA. Unusual infections from organisms that rarely cause trouble in healthy people, like oral yeast infections (thrush) or cytomegalovirus, can also trigger the test.
Beyond infections, doctors order IgA tests as part of screening for celiac disease, evaluating suspected kidney disease, and investigating certain blood cancers. The test is also used when someone shows signs of a broader immune deficiency, often alongside IgG and IgM measurements to get a complete picture.
IgA and Celiac Disease Screening
One of the most common reasons for an IgA test is celiac disease screening. The standard celiac blood test looks for a specific antibody called tissue transglutaminase IgA (tTG-IgA). The catch: if your total IgA level is very low, that screening test can come back falsely negative, missing celiac disease entirely.
For this reason, many labs now run a total IgA measurement first. If the level is normal, they proceed with the standard tTG-IgA test. If total IgA is low, they switch to IgG-based tests instead, which remain reliable even when IgA is deficient. This matters because selective IgA deficiency is more common in people with celiac disease than in the general population, so the two conditions overlap in ways that can complicate diagnosis if total IgA isn’t checked.
IgA Nephropathy
IgA nephropathy (also called Berger’s disease) is a kidney condition where abnormal IgA deposits build up in the kidney’s filtering units, causing inflammation and progressive damage. You might expect a blood IgA test to be the go-to diagnostic tool here, but serum IgA levels alone lack the sensitivity and specificity to confirm or rule out the condition. Some patients with IgA nephropathy have elevated blood IgA, but many don’t.
Researchers have identified a modified form of IgA, called galactose-deficient IgA, that’s elevated in about 77% of patients with the disease and is absent in 94% of people without it. Still, the gold standard for diagnosis is a kidney biopsy, where pathologists look for IgA deposits directly in the tissue using immunofluorescence microscopy. A blood IgA level might prompt further investigation, but it won’t confirm the diagnosis on its own.
What Low IgA Levels Mean
Selective IgA deficiency is the most common primary immune deficiency. It’s defined as a blood IgA level below 7 mg/dL in someone older than four years who has normal IgG and IgM levels. Prevalence varies by ethnicity, ranging from about 1 in 143 to 1 in 965 people, and it affects men and women equally.
Most people with selective IgA deficiency never develop symptoms. Those who do typically experience recurrent respiratory or gastrointestinal infections. The condition is also associated with a higher risk of autoimmune diseases and allergies. Because IgG and IgM remain intact, the immune system usually compensates well enough that many people go their whole lives without knowing they have it.
When IgA is low alongside IgG, the picture changes. Low levels of both suggest a more significant immune deficiency called common variable immune deficiency (CVID), which is the most common serious primary antibody deficiency in children and adults. CVID typically requires ongoing treatment, so distinguishing it from isolated IgA deficiency matters.
Secondary causes of low IgA are actually more common than inherited ones. Certain medications, including some anticonvulsants and immune-suppressing drugs, can lower antibody levels. Conditions that cause protein loss, like nephrotic syndrome or protein-losing gut disease, can also deplete immunoglobulins, though IgM often stays normal in those cases because it’s a larger molecule that isn’t lost as easily.
What High IgA Levels Mean
Elevated IgA can point to chronic infections, inflammatory conditions, or liver disease. Cirrhosis is a well-known cause of raised IgA. Chronic inflammatory conditions like inflammatory bowel disease and some autoimmune disorders can also push levels up.
More concerning, very high IgA may indicate an IgA-producing blood cancer such as multiple myeloma or a precancerous condition called monoclonal gammopathy. In these conditions, a single clone of immune cells produces large quantities of identical IgA antibodies. IgA myeloma tends to carry a less favorable prognosis compared to other myeloma types.
Normal IgA Ranges by Age
IgA levels are extremely low at birth and rise steadily throughout childhood. Newborns typically have levels under 9 mg/dL, while teenagers between 16 and 18 average between 168 and 235 mg/dL. The standard adult reference range at most labs falls roughly between 70 and 400 mg/dL, though exact numbers vary by laboratory.
This age-dependent rise is why selective IgA deficiency isn’t diagnosed before age four. Young children naturally have low IgA, and their levels may still be catching up. Testing too early can produce a misleading result.
How the Test Works
The IgA test is a simple blood draw. No fasting is required. Results are usually available within a few days. In some cases, particularly when the main symptoms involve frequent colds, sinus infections, or diarrhea, your doctor may also order a saliva-based IgA test to measure levels at the mucosal surface directly.
IgA is rarely measured in isolation. Doctors typically order it as part of an immunoglobulin panel that includes IgG and IgM. The pattern across all three antibody types helps distinguish between different conditions. Isolated low IgA with normal IgG and IgM points to selective IgA deficiency. Low IgG and IgA together suggests CVID. A spike in one immunoglobulin type with suppression of the others raises concern for a blood cancer. The combination tells a story that no single number can.