Your Mucosal Shield Antibody
IgA is your body's mucosal bouncer—it patrols the lining of your gut, lungs, and urinary tract, preventing pathogens from gaining entry. It's the most abundantly produced antibody in the body (mostly secretory IgA in mucous membranes). Selective IgA deficiency is the most common primary immunodeficiency (~1 in 500 people).
What is IgA (Immunoglobulin A)?
IgA exists in two forms: serum IgA (monomeric) and secretory IgA (dimeric, found in mucous membranes). Two subclasses: IgA1 (85%) and IgA2 (15%). IgA deficiency is defined as <7 mg/dL with normal IgG and IgM in patients >4 years old.
↑ What High IgA (Immunoglobulin A) Means
IgA nephropathy (kidney disease), celiac disease, chronic liver disease, respiratory infections, or IgA myeloma. IgA nephropathy is the most common glomerulonephritis worldwide.
Common symptoms:
If IgA nephropathy: blood in urine (especially after respiratory infection), protein in urine · If liver disease: symptoms of underlying liver condition
↓ What Low IgA (Immunoglobulin A) Means
Selective IgA deficiency: most people are asymptomatic. Some have recurrent sinopulmonary and GI infections. Important: IgA-deficient patients can have anaphylactic reactions to blood products containing IgA.
Common symptoms:
Usually asymptomatic · Some: recurrent sinopulmonary infections, chronic diarrhea · Risk of anaphylactic reaction to blood products
Why It Matters
When normal:
Primary mucosal immune defense
IgA deficiency is common and usually benign
Elevated IgA: screens for IgA nephropathy and celiac disease
Transfusion alert: IgA-deficient patients need IgA-depleted products
Risks if abnormal:
Deficiency: usually asymptomatic but risk of transfusion reactions
IgA deficiency + celiac: higher prevalence of celiac disease
Elevated: IgA nephropathy, alcoholic liver disease
What Can Cause Abnormal Levels?
Selective IgA Deficiency (low)
35% likelyMost common primary immunodeficiency (~1:500). Most people are asymptomatic.
IgA Nephropathy (high)
30% likelyIgA deposits in kidneys causing glomerulonephritis. Elevated serum IgA in ~50%.
Celiac Disease (associated with deficiency)
IgA deficiency is 10-15x more common in celiac patients. Must use IgG-based celiac testing.
Liver Disease (high)
Alcoholic liver disease classically elevates IgA more than IgG or IgM.
Medications (low)
Phenytoin, carbamazepine, and some immunosuppressants can lower IgA.
What You Can Do
If IgA deficient: medical alert bracelet recommended
Impact: Prevents anaphylactic transfusion reactions \u00B7 Timeline: Lifelong
Screen for celiac disease if IgA deficient (use IgG-based tests)
Impact: Standard celiac test (IgA-tTG) will be falsely negative \u00B7 Timeline: One-time
If lifestyle changes aren't enough:
If elevated IgA: check urine for blood/protein (IgA nephropathy screen)
Impact: IgA nephropathy is the most common glomerulonephritis \u00B7 Timeline: One-time
Recommended retest: Confirm deficiency with repeat testing; IgA nephropathy: monitor kidney function
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