An elevated Immunoglobulin A (IgA) level often concerns people reviewing their lab results. While IgA is involved in certain blood cancers, it is far more frequently a marker for common, non-malignant conditions like infection or inflammation. IgA is a class of antibody, a protein produced by the immune system to identify and neutralize foreign objects such as bacteria and viruses. Understanding IgA’s normal function provides context for interpreting why its level might be high.
The Role of Immunoglobulin A (IgA)
IgA is the most abundant antibody in the body’s mucosal immune system, serving as a primary defense mechanism. These antibodies are strategically located in secretions that bathe mucosal surfaces, including the lining of the respiratory and gastrointestinal tracts, saliva, tears, and breast milk. IgA production in these areas is greater than all other antibody types combined, emphasizing its role as a first line of defense.
The IgA found on these surfaces is known as secretory IgA. It is typically a dimeric structure, protected from degradation by a secretory component, allowing it to survive harsh environments like the gut. In contrast, the IgA measured in a standard blood test, or serum IgA, is predominantly a monomeric, single unit. Serum IgA levels rise when the body responds to systemic inflammation or infection, often reflecting an overspill of the mucosal response into the bloodstream.
Common Causes of Elevated IgA
Non-malignant reasons for high IgA levels relate mainly to the immune system’s normal function of combating invaders or dealing with chronic inflammation. Since IgA protects mucosal surfaces, chronic or recurrent infections, especially those affecting the respiratory or gastrointestinal tract, frequently cause elevation. Viral conditions like chronic hepatitis or HIV stimulate a sustained rise in IgA as the body attempts to control the viral load.
Chronic inflammation from autoimmune diseases can also lead to persistently high IgA levels, such as in rheumatoid arthritis, systemic lupus erythematosus (SLE), and celiac disease. Liver diseases, especially alcoholic cirrhosis and chronic hepatitis, are strongly associated with increased serum IgA. This is often due to impaired clearance of IgA by the damaged liver or increased immune activity. Inflammatory bowel diseases are another category of chronic conditions that can cause IgA levels to rise.
Specific Malignancies Associated with High IgA
While most IgA elevations are benign, a significant and sustained increase can signal certain cancers involving plasma cells or the lymphatic system. The most direct link is with Immunoglobulin A Myeloma, which is the second most common type of multiple myeloma, a cancer of the plasma cells in the bone marrow. In IgA Myeloma, a single, abnormal clone of plasma cells produces a massive amount of identical, non-functional IgA, known as a monoclonal protein or M-protein.
The presence of this monoclonal protein, sometimes called a monoclonal spike, is the key difference between a malignant elevation and the polyclonal rise seen with infection. A polyclonal elevation is a generalized increase in various IgA antibodies, reflecting a broad, normal immune response. Cancers like certain lymphomas, such as Mucosa-Associated Lymphoid Tissue (MALT) lymphoma, may also be associated with elevated IgA. High IgA has also been studied in other mucosal cancers, including those of the bladder and the oral cavity.
Interpreting Results and Follow-Up Testing
An elevated IgA level alone is not sufficient for a cancer diagnosis; it prompts further investigation into the underlying cause. The first step in clinical follow-up is determining if the IgA elevation is polyclonal (pointing toward chronic infection or inflammation) or monoclonal (suggestive of a plasma cell disorder). This distinction is typically made using a specialized blood test called Serum Protein Electrophoresis (SPEP).
SPEP separates blood proteins to look for a distinct band or “spike” indicating a monoclonal protein. Because IgA monoclonal proteins can be difficult to quantify accurately with SPEP, quantitative immunoglobulin testing is often used alongside it. If a monoclonal spike is detected, further evaluation may include a bone marrow biopsy to examine the plasma cells directly and confirm a diagnosis like IgA Myeloma.