The human body’s defense system relies on specialized proteins called immunoglobulins, or antibodies, to identify and neutralize foreign invaders. Immunoglobulin A (IgA) is one of the five main classes of these antibodies, and it plays a distinct role in protecting the body’s surfaces. Measuring the level of IgA in the blood is a routine test used to assess immune health, particularly when investigating recurrent infections, autoimmune conditions, or certain gastrointestinal issues. Understanding what constitutes a normal IgA level is the first step in interpreting the results of this common blood test.
The Role of Immunoglobulin A in Immunity
Immunoglobulin A is the most abundantly produced antibody in the body, reflecting its role as a primary defense agent at external-facing sites. It is found in two major forms. The vast majority is secretory IgA (SIgA), found in external secretions such as saliva, tears, breast milk, and the mucus lining the respiratory and digestive tracts.
This secretory form is a dimer, consisting of two antibody units, and possesses a unique component that protects it from enzymes found in harsh environments like the gut. Its main function is immune exclusion, trapping pathogens and toxins in the mucus layer, preventing them from attaching to cells. The remaining IgA is serum IgA, which circulates in the blood, primarily in a monomeric form, and constitutes about 10 to 15% of the total antibodies in the serum.
Defining the Normal Range for IgA
When a blood test measures IgA, it is primarily assessing the concentration of serum IgA circulating in the bloodstream. For adults, the typical normal reference range for IgA is between 70 and 400 milligrams per deciliter (mg/dL). This range is not universal and can vary slightly between different laboratories based on the specific testing method, equipment, and population demographics used to establish their reference values.
A person’s age is a significant factor, as children and adolescents have different normal ranges compared to adults. A healthcare provider interprets a test result by comparing it to the reference range printed on the laboratory report. A result falling outside this established range suggests an alteration in immune function that may warrant further investigation.
Clinical Implications of Low IgA Levels
A low IgA level, known as hypogammaglobulinemia, can indicate an underlying immune deficiency, making a person more susceptible to infections. The most common form of this condition is Selective IgA Deficiency (SIgAD), which is the most frequent primary immunodeficiency, affecting approximately one in 500 individuals in some populations. SIgAD is defined by an IgA level in the blood below 7 mg/dL, while the levels of other antibodies like IgG and IgM remain normal. Many individuals with SIgAD remain asymptomatic throughout their lives, often unaware of their deficiency.
For those who are symptomatic, the lack of mucosal protection can lead to recurrent infections, particularly in the respiratory tract and the gastrointestinal system. These infections can include frequent sinus or lung infections, as well as chronic diarrhea or giardiasis. A low IgA level is also associated with an increased risk of developing autoimmune diseases, such as celiac disease, systemic lupus erythematosus (SLE), and rheumatoid arthritis.
A significant concern for those with severely low IgA is the rare but serious risk of an anaphylactic reaction if they receive blood products containing IgA. Specialized IgA-deficient or washed blood products are often recommended. Treatment is usually supportive, focusing on managing the recurrent infections and associated conditions, rather than replacing the missing IgA directly.
Clinical Implications of Elevated IgA Levels
An elevated IgA level, or hypergammaglobulinemia, indicates that the immune system is highly active in response to a stimulus. Since IgA is heavily involved in mucosal defense, chronic or acute infections, particularly those affecting the respiratory or digestive systems, can cause a rise in its concentration. The sustained presence of pathogens or inflammation at the mucosal surfaces drives the increased production of this antibody.
Elevated IgA can also be a marker for certain autoimmune and inflammatory diseases. Conditions like IgA nephropathy (Berger’s disease), where IgA deposits accumulate in the kidneys, are directly linked to high IgA levels. Liver diseases, such as cirrhosis or chronic hepatitis, are another common cause for this elevation. In rare cases, extremely high IgA levels can be a sign of a plasma cell disorder, such as IgA multiple myeloma.