Overview
Immunoglobulin A (IgA) is one of the five main antibodies produced by the immune system (IgG, IgA, IgM, IgD, IgE). IgA plays an essential role in protecting the surfaces of the body that are exposed to the outside environment, especially areas like the nose, mouth, lungs, stomach, intestines, urinary tract, and reproductive tract.
Unlike other antibodies that circulate mainly in the bloodstream, IgA is found in mucous membranes and body secretions including:
- Saliva
- Tears
- Mucus
- Breast milk
- Intestinal and respiratory fluids
Because IgA protects the body at entry points, it acts as the first line of defense against infections.
The IgA blood test measures the amount of Immunoglobulin A present in the bloodstream. Doctors use this test to diagnose immune deficiencies, chronic infections, digestive disorders, and autoimmune diseases such as celiac disease.
Where Is IgA Produced in the Body?
IgA is produced by plasma cells, which are specialized white blood cells created from B-lymphocytes. These plasma cells are mainly found in:
- Peyer’s patches (lymphoid tissue in the small intestine)
- Tonsils
- Respiratory tract mucosa
- Gastrointestinal mucosa
- Salivary glands
- Lacrimal glands (tear glands)
- Mammary glands (breast milk production)
There are two main forms of IgA:
1. Serum IgA
Found in blood; tested in routine blood samples.
2. Secretory IgA (sIgA)
Found in secretions like saliva, tears, and breast milk.
This form is especially important for protecting mucous membranes and the digestive system.
Main Functions and Importance of IgA
IgA has several vital roles in the immune system:
1. First line of defense at mucosal surfaces
IgA prevents bacteria, viruses, and toxins from attaching to the lining of the gut, lungs, throat, urinary tract, and reproductive tract.
2. Neutralizes pathogens
IgA binds to harmful organisms and stops them from entering deeper tissues.
3. Maintains healthy gut microbiota
It helps balance good bacteria in the intestine and prevents harmful organisms from overgrowing.
4. Provides immunity to newborns
IgA in breast milk gives protection to infants while their immune system is developing (passive immunity).
5. Helps diagnose immune disorders
IgA levels can help identify:
- Celiac disease
- Chronic infections
- Selective IgA deficiency
- Autoimmune diseases
This makes the test helpful for both adults and children.
Causes of Low / Negative IgA Levels
Low IgA levels may occur for different reasons:
1. Selective IgA Deficiency
The most common cause. It is the most frequent primary immunodeficiency worldwide and often genetic.
2. Genetic immune disorders
Some inherited conditions affect the body’s ability to produce IgA.
3. Medications
Certain treatments can reduce IgA production:
- Immunosuppressants
- Chemotherapy
- Anti-seizure drugs
4. Protein-losing conditions
These cause the body to lose IgA through urine or damaged tissues:
- Nephrotic syndrome
- Severe burns
- Protein-losing enteropathy
Symptoms of Low IgA Levels
Many people with low IgA levels have no symptoms at all, especially those with selective IgA deficiency.
But if symptoms occur, they may include:
Respiratory Infections
- Sinus infections
- Bronchitis
- Pneumonia
Gastrointestinal Problems
- Diarrhea
- Chronic stomach infections
- Giardiasis (parasitic infection)
Allergies and Asthma
Low IgA is linked to higher rates of allergic diseases.
Autoimmune Conditions
Low IgA increases the risk of:
- Celiac disease
- Rheumatoid arthritis
- Lupus (SLE)
Causes of High / Positive IgA Levels
High IgA levels usually indicate chronic or long-lasting health problems:
1. Chronic Infections
Especially those affecting the:
- Respiratory tract
- Digestive tract
2. Autoimmune Diseases
High IgA is often seen in:
- Celiac disease
- Rheumatoid arthritis
- Systemic lupus erythematosus (SLE)
3. Liver Diseases
Including:
- Cirrhosis
- Chronic hepatitis
4. IgA Myeloma
A rare cancer of plasma cells in which IgA levels become extremely elevated.
Symptoms of High IgA Levels
Symptoms depend entirely on the underlying condition causing the high IgA.
Autoimmune Disease
- Joint pain
- Fatigue
- Skin rashes
- Digestive problems
Liver Disease
- Jaundice (yellowing of skin)
- Swollen abdomen
- Weakness
- Loss of appetite
Chronic Infection
- Persistent cough
- Fever
- Diarrhea
- Ongoing fatigue
Multiple Myeloma (IgA type)
- Bone pain
- Anemia
- Repeated infections
- Unexplained weight loss
Reference Ranges
The normal range depends on age and lab standards:
Adults
70 – 400 mg/dL
Children
Lower than adults; gradually rises with age.
Levels outside this range require interpretation by a doctor based on symptoms and medical history.
Sample Type
The most common sample is a blood sample (serum) taken from a vein.
Other sample options when evaluating secretory IgA (sIgA):
- Saliva
- Stool
- Breast milk
These are usually for digestive or mucosal immunity assessments.
Test Preparation
No major preparation is needed.
- No fasting required
- Continue regular medications unless doctor says otherwise
- Inform your doctor about autoimmune disorders, digestive issues, or frequent infections
- For children, bring previous medical records if available
When to Consult a Doctor
You should contact a doctor if you have:
- Frequent sinus or chest infections
- Chronic diarrhea or digestive issues
- Symptoms of celiac disease
- Persistent cough or fever
- Joint pain with fatigue
- Signs of liver disease
- Family history of immune deficiency
- Delayed growth or repeated infections in children
Doctors may advise an IgA test along with IgG and IgM for full immune evaluation.
Important Word Explanations
- Antibody: A protein made by the immune system to fight germs.
- Mucosal surfaces: Areas like the gut, nose, lungs, and urinary tract.
- Peyer’s patches: Immune tissue in the small intestine.
- Selective IgA Deficiency: A condition where the body can’t produce enough IgA.
- Autoimmune disease: When the immune system mistakenly attacks the body.
- sIgA: Secretory IgA found in fluids like saliva and breast milk.
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