What this test measures
Immunoglobulin A (IgA) is the antibody class that dominates mucosal surfaces — the lining of the airways, gut, urogenital tract, and saliva. It is also present in blood, where it makes up about 15% of total immunoglobulin. The serum IgA test quantifies all IgA in blood (IgA1 + IgA2 subclasses), reported in mg/dL.
Selective IgA deficiency (serum IgA < 7 mg/dL with normal IgG and IgM) is the most common primary immunodeficiency in humans, affecting roughly 1 in 500 adults in Indian and Western populations.
Why it matters
IgA testing has two main clinical uses. First, immunodeficiency workup — selective IgA deficiency causes recurrent sinopulmonary infections, increased atopy, and higher autoimmune risk. It is also important to screen for in celiac disease testing because patients with IgA deficiency give false-negative results on IgA-based celiac antibodies (tTG IgA, DGP IgA).
Second, in suspected plasma-cell disorders — IgA myeloma is the second most common heavy-chain class (after IgG myeloma). High serum IgA with M-protein on serum protein electrophoresis and abnormal free light chains supports IgA myeloma or MGUS. Elevated IgA also occurs in chronic liver disease (alcoholic cirrhosis classically raises IgA), IgA nephropathy, chronic infection, and autoimmune disease.
How to prepare
No fasting required. Continue all medications. Disclose any history of recurrent infections, IgA deficiency, celiac disease workup, plasma cell disorder, or liver disease. IgA can be transiently raised during acute infection — interpret in context.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Immunoglobulin A (mg/dL)[1][2][3] | Adult 70 – 400 mg/dL (lab-specific) | < 70 mg/dL: low IgA. < 7 mg/dL with normal IgG and IgM = selective IgA deficiency. Also low in common variable immunodeficiency (CVID), X-linked agammaglobulinaemia, hyper-IgM syndrome, ataxia-telangiectasia, severe protein-losing states, and immunosuppressive therapy. | > 400 mg/dL: chronic liver disease (especially alcoholic cirrhosis), chronic infection, autoimmune disease (RA, SLE), IgA nephropathy, IgA myeloma or MGUS (with M-spike on SPEP). In children, age-specific reference ranges apply (IgA is naturally lower in young children). |
Where IgA matters clinically
| Clinical setting | IgA pattern |
|---|---|
| Selective IgA deficiency | IgA < 7 mg/dL; normal IgG and IgM |
| Celiac disease workup (screen) | Total IgA alongside tTG IgA |
| IgA myeloma / MGUS | High IgA with M-spike on SPEP |
| Chronic alcoholic liver disease | High IgA (sometimes IgA > IgG) |
| IgA nephropathy (Berger disease) | Elevated IgA in ~50% of patients |
Frequently asked questions
What is selective IgA deficiency?
The most common primary immunodeficiency in humans (~1 in 500). Serum IgA is essentially absent (< 7 mg/dL) but other immunoglobulins are normal. Many people are asymptomatic; some have recurrent sinopulmonary infections, gut infections (especially Giardia), atopic disease, or autoimmune disorders.
Why does IgA deficiency matter for celiac disease testing?
Standard celiac disease antibody tests (tTG IgA, DGP IgA) are IgA-based — they give false-negative results in IgA-deficient patients. That is why total IgA is always tested alongside tTG IgA. If IgA is low, switch to IgG-based celiac antibodies.
Are blood transfusions risky in IgA deficiency?
A small subset of IgA-deficient patients develop anti-IgA antibodies and can have severe anaphylactic transfusion reactions. These patients need washed red cells or IgA-deficient blood products. Discuss this with your doctor before any planned transfusion or IV immunoglobulin.
What does high IgA mean?
In adults, common causes are chronic liver disease (especially alcoholic), chronic infection, autoimmune disease, and IgA myeloma or MGUS. A high IgA with an M-protein band on serum protein electrophoresis warrants haematology evaluation.
What is IgA nephropathy?
IgA nephropathy (Berger disease) is the world's most common primary glomerulonephritis — common in Indian and Asian populations. IgA immune complexes deposit in the glomerulus, causing haematuria (often visible after viral upper-respiratory infection), proteinuria, and progressive kidney disease. Serum IgA is raised in about half of patients but is not diagnostic alone.
Should children be tested with the same reference range?
No — IgA is naturally lower in young children and rises through childhood to adult levels by adolescence. Always interpret paediatric IgA against age-specific reference ranges.
Related Immunology tests
Tests commonly ordered alongside IMMUNOGLOBULIN A (IGA), or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Immunoglobulin Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Immunoglobulin A · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Immunoglobulin A · accessed 2026-05-30T00:00:00.000Z
- AAAAI — Primary Immunodeficiency · accessed 2026-05-30T00:00:00.000Z
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