What does low Immunoglobulin A (IgA) mean?

From the Guidelines

Low Immunoglobulin A (IgA) means your body has significantly reduced levels of IgA antibodies, typically less than 7 mg/dL, which is crucial for protecting mucous membranes in your respiratory and digestive tracts against infections. This condition, called Selective IgA Deficiency (SIGAD), is the most common primary immunodeficiency disorder, affecting approximately 1 in 300 to 700 white subjects in the United States 1. Most people with low IgA have no symptoms because other antibodies compensate, but some may experience recurrent respiratory infections, gastrointestinal issues, allergies, or autoimmune disorders. Diagnosis involves blood tests measuring immunoglobulin levels, and it's essential to note that patients with serum IgA levels of less than the normal range for age but greater than 7 mg/dL should not be given a diagnosis of IgA deficiency 1.

Key Points to Consider

• SIGAD is characterized by low or absent IgA levels, with approximately two thirds of subjects having a lower detectable level of IgA, and one third having completely absent IgA 1.
• Patients with SIGAD should be monitored over time for the occurrence of complications, such as respiratory and gastrointestinal tract infections, atopy, autoimmune diseases, celiac disease, and malignancy 1.
• Impaired specific antibody responses, particularly to pneumococcal polysaccharide, are also seen in patients with SIGAD, and some may have lower rates of switched memory B cells, leading to higher rates of pneumonia, bronchiectasis, and autoimmune disease 1.
• Management of SIGAD focuses on treating infections promptly with antibiotics when they occur, and for those with frequent infections, preventive antibiotics might be prescribed 1.
• In severe cases, immunoglobulin replacement therapy may be considered, though standard preparations contain little IgA, and patients with IgA deficiency are considered to be at risk for anaphylactic reactions to blood products 1.

From the Research

Definition of Low IgA

• Low Immunoglobulin A (IgA) refers to a condition where the levels of IgA antibodies in the blood are lower than normal [(2,3,4,5,6)].
• Selective IgA deficiency (SIgAD) is defined as a serum IgA level of less than 0.07g/L in patients greater than 4 years old with normal levels of IgG and IgM 3.

Causes and Prevalence

• SIgAD is the most common primary immunodeficiency, with a prevalence of approximately 1/600 in whites 4.
• The exact cause of SIgAD is still unknown, but it is presumed to be related to a defective terminal differentiation of B cells and defect in switching to IgA-producing plasma cells 6.

Clinical Complications

• Patients with low IgA levels may experience recurrent respiratory and gastrointestinal infections [(2,3,4,5,6)].
• Other clinical complications associated with SIgAD include autoimmune and allergic manifestations, inflammatory gastrointestinal disease, and malignancy [(3,5)].

Diagnosis and Management

• Diagnosis of SIgAD is based on serum IgA levels and exclusion of secondary causes of hypogammaglobulinemia 3.
• Management of SIgAD involves monitoring at regular intervals, education on potential complications, and prophylactic antibiotics in some cases 5.
• Immunoglobulin replacement therapy may be considered in patients with SIgAD and concomitant IgG subclass deficiency 3.