Immunoglobulin A (IgA) is a major class of antibody produced by the body’s immune system to help fight off illness. Measuring IgA in a child’s bloodstream is a common diagnostic step when investigating frequent or unusual infections. These measurements provide a snapshot of the humoral immune status. Understanding the reported IgA number requires context, as what constitutes a “normal” level changes dramatically from infancy through adolescence.
The Role of Immunoglobulin A in Pediatric Health
IgA is the most abundant antibody in mucosal secretions, serving as the body’s primary defense at surfaces exposed to the external environment. These surfaces include the mucous membranes lining the respiratory tract, the gastrointestinal system, and the genitourinary tract. This antibody is also present in saliva, tears, and breast milk, where it provides passive immunity to infants.
This defensive IgA is known as Secretory IgA (sIgA) and functions by binding to foreign substances like bacteria, viruses, and toxins. This process, called immune exclusion, prevents pathogens from adhering to the mucosal lining and entering the body’s tissues. The small amount of IgA found circulating in the blood, known as serum IgA, helps clear the body of antigens that may have penetrated the mucosal barrier.
Understanding Age-Specific IgA Reference Ranges
A child’s IgA level is highly dependent on their age. At birth, IgA levels are virtually absent because this antibody does not cross the placenta from the mother. The child’s immune system begins producing its own IgA after birth, and the concentration slowly rises throughout childhood.
Because of this gradual maturation process, the definition of a “normal” level shifts significantly across pediatric age groups. For an infant under six months, an IgA level that would be considered low for an older child may be appropriate. The IgA concentration typically does not reach adult levels until a child is between 15 and 18 years old.
General reference ranges illustrate this development, though actual values vary by laboratory and testing method. For children aged one to three years, the typical range for serum IgA falls between 0 and 100 milligrams per deciliter (mg/dL). By the age of six to fourteen years, the expected normal range may increase to between 50 and 240 mg/dL. The steady increase reflects the continuous development of the mucosal immune system as the child encounters new environmental challenges.
Clinical Implications of Abnormal IgA Levels
Results that fall outside the established age-specific range require careful interpretation by a healthcare professional. A low IgA level is the more common finding.
Low IgA Levels and Selective IgA Deficiency (sIgAD)
A low IgA level may lead to a diagnosis of Selective IgA Deficiency (sIgAD), the most frequent primary immunodeficiency. This condition is defined by a serum IgA level below 7 mg/dL in a child over four years old, while other antibody levels remain normal. Many children with sIgAD are asymptomatic and lead completely healthy lives, never experiencing significant illness. However, others may experience recurrent infections, particularly in the respiratory tract (such as ear, sinus, or lung infections) and the gastrointestinal tract. This deficiency can also be associated with an increased occurrence of autoimmune conditions like celiac disease, systemic lupus erythematosus, and rheumatoid arthritis.
Elevated IgA Levels
Conversely, an elevated IgA level, sometimes referred to as hyper-IgA, is less specific but can also be clinically significant. High IgA levels are often a non-specific indicator of an active or chronic inflammatory state or an ongoing infection. In pediatric patients, IgA levels exceeding approximately 368 mg/dL may raise suspicion for certain underlying conditions. These elevated levels can be linked to chronic liver disease, inflammatory bowel disease, or specific rheumatological disorders. Conditions like IgA nephropathy or IgA vasculitis (Henoch-Schönlein purpura) are also associated with increased IgA production. An abnormal IgA result, whether high or low, serves as an alert that warrants a comprehensive evaluation and should always be discussed with the child’s pediatrician for personalized interpretation.