IgA

Immunoglobulin A

Immune & Inflammation

What is Immunoglobulin A?

Immunoglobulin A (IgA) is an antibody that plays a critical role in mucosal immunity—the defense system protecting the body's surfaces that are exposed to the outside environment. IgA is the most abundantly produced immunoglobulin in the human body and is the dominant antibody in secretions including saliva, tears, breast milk, and the mucous lining of the respiratory, gastrointestinal, and genitourinary tracts. It exists in two forms: serum IgA (predominantly monomeric) circulating in the blood, and secretory IgA (dimeric, joined by a J chain and secretory component) found on mucosal surfaces.

Serum IgA accounts for approximately 10–15% of total serum immunoglobulins. It is produced by plasma cells in the bone marrow and mucosa-associated lymphoid tissue (MALT). Secretory IgA functions as a first-line barrier by binding pathogens and toxins on mucosal surfaces, preventing their attachment and entry into the body—a process called immune exclusion. Quantitative measurement of serum IgA is used to evaluate immunodeficiency, diagnose IgA nephropathy, screen for celiac disease, and assess certain autoimmune and lymphoproliferative conditions.

Why It Matters

IgA is the body's frontline mucosal defender. Selective IgA deficiency is the most common primary immunodeficiency, affecting approximately 1 in 300–500 individuals, and is associated with increased susceptibility to respiratory and gastrointestinal infections, autoimmune diseases, and allergies. Elevated IgA is the hallmark of IgA nephropathy (Berger disease)—the most common form of glomerulonephritis worldwide—and can also indicate IgA myeloma, liver cirrhosis, or chronic mucosal infections. IgA antibodies against tissue transglutaminase (tTG-IgA) are the primary screening test for celiac disease.

Normal Reference Ranges

GroupRangeUnit
Adults70–400mg/dL
Children (6–12 years)50–250mg/dL
Children (1–5 years)20–160mg/dL
Neonates1–5mg/dL

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High IgA Levels Mean

Common Causes

  • IgA nephropathy (Berger disease)
  • IgA myeloma (multiple myeloma, IgA subtype)
  • Liver cirrhosis (alcoholic and non-alcoholic)
  • Chronic infections (respiratory, GI)
  • Inflammatory bowel disease
  • Celiac disease
  • Autoimmune disorders (rheumatoid arthritis, SLE)
  • Henoch-Schönlein purpura (IgA vasculitis)

Possible Symptoms

  • Hematuria (blood in urine, in IgA nephropathy)
  • Abdominal or flank pain
  • Purpuric rash on lower extremities (IgA vasculitis)
  • Joint pain
  • Recurrent infections
  • Fatigue and weight loss (in myeloma)
  • Signs of liver disease (in cirrhosis)

What to do: Markedly elevated IgA should prompt serum protein electrophoresis (SPEP) and immunofixation to evaluate for IgA myeloma. If hematuria is present, evaluate for IgA nephropathy with urinalysis, kidney function tests, and possibly kidney biopsy. Elevated IgA with liver disease markers suggests cirrhosis. Henoch-Schönlein purpura is diagnosed clinically by the characteristic purpuric rash, arthritis, abdominal pain, and renal involvement. Treat the underlying condition.

What Low IgA Levels Mean

Common Causes

  • Selective IgA deficiency (most common primary immunodeficiency)
  • Common variable immunodeficiency (CVID)
  • Ataxia-telangiectasia
  • Medications (phenytoin, carbamazepine, immunosuppressants)
  • Nephrotic syndrome (protein loss)
  • Chronic lymphocytic leukemia
  • X-linked agammaglobulinemia

Possible Symptoms

  • Recurrent sinopulmonary infections
  • Chronic diarrhea and gastrointestinal infections
  • Allergies and asthma (increased prevalence)
  • Autoimmune conditions (thyroiditis, celiac disease, lupus)
  • Many individuals with IgA deficiency are completely asymptomatic

What to do: If IgA is undetectable (<7 mg/dL), confirm selective IgA deficiency by checking IgG and IgM levels (which should be normal in isolated IgA deficiency). Patients with IgA deficiency should be warned about the risk of anaphylactic transfusion reactions to IgA-containing blood products—they can develop anti-IgA antibodies. Celiac disease screening in IgA-deficient patients requires IgG-based tests (tTG-IgG or deamidated gliadin IgG) since standard IgA-based tests will be falsely negative.

When Is IgA Testing Recommended?

  • When recurrent sinopulmonary or gastrointestinal infections suggest immunodeficiency
  • When evaluating hematuria for possible IgA nephropathy
  • As part of an immunoglobulin panel in immune workup
  • Before celiac disease screening (to rule out IgA deficiency)
  • When IgA myeloma is suspected
  • When evaluating IgA vasculitis (Henoch-Schönlein purpura)

Frequently Asked Questions

Selective IgA deficiency is the most common primary immunodeficiency, defined as serum IgA below 7 mg/dL with normal IgG and IgM levels in a person over age 4. It affects approximately 1 in 300–500 Caucasians and is less common in other ethnic groups. Most people with IgA deficiency are asymptomatic and never diagnosed, but some experience recurrent respiratory and GI infections, allergies, or autoimmune diseases at higher rates. There is no specific treatment for the deficiency itself—management focuses on treating infections promptly and being aware of transfusion risks.
The standard screening test for celiac disease is tissue transglutaminase IgA (tTG-IgA). In patients with IgA deficiency, this test will be falsely negative because the patient cannot produce IgA antibodies of any type. Since celiac disease is 10–15 times more common in IgA-deficient individuals than in the general population, this is clinically important. IgA-deficient patients should be screened using IgG-based tests such as tTG-IgG or deamidated gliadin peptide IgG. Total IgA should ideally be checked alongside any celiac screening panel.
IgA nephropathy (Berger disease) is the most common form of glomerulonephritis worldwide. It occurs when abnormally glycosylated IgA1 molecules form immune complexes that deposit in the glomerular mesangium, triggering inflammation and kidney damage. The classic presentation is episodic gross hematuria (visible blood in urine) occurring 1–2 days after an upper respiratory infection ("synpharyngitic hematuria"), though many patients have only persistent microscopic hematuria. Approximately 20–40% of patients progress to end-stage renal disease over 20 years. Treatment includes blood pressure control with ACE inhibitors/ARBs, and immunosuppression for progressive disease.
IgA-deficient patients can develop anti-IgA antibodies (class IgE or IgG), which puts them at risk for severe anaphylactic transfusion reactions when they receive standard blood products containing IgA. While this risk is relatively low (estimated 1 in 20,000–50,000 transfusions), it can be life-threatening. Patients with known IgA deficiency should carry a medical alert indicating their condition. When transfusion is needed, washed red blood cells (which have IgA removed) or blood products from IgA-deficient donors should be used. Standard intravenous immunoglobulin (IVIG) also contains IgA and may need to be substituted with IgA-depleted preparations.
In liver cirrhosis, serum IgA rises due to several mechanisms. The cirrhotic liver has impaired clearance of IgA immune complexes from the portal circulation (normally the liver removes secretory IgA via hepatic receptors). Additionally, portal hypertension leads to increased bacterial translocation from the gut, stimulating mucosal IgA production. Chronic alcohol use directly stimulates IgA-producing plasma cells. Elevated IgA in liver disease is polyclonal (unlike the monoclonal elevation in IgA myeloma) and correlates with disease severity.

Related Biomarkers

IgMImmunoglobulin MIgGImmunoglobulin GCRPC-Reactive ProteinCrCreatinineWBCWhite Blood Cells

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.