Immunoglobulin A (IgA) Test: Normal Levels & Meaning

Immunoglobulin A (IgA) Blood Test: A Comprehensive Guide

When a patient comes to my clinic with recurrent sinus infections or a family history of autoimmune conditions, one of the first tests I order is Immunoglobulin A (IgA). This antibody is the silent sentinel of your mucosal surfaces—your gut, respiratory tract, and eyes. Unlike the dramatic responses of IgE allergies, IgA works quietly, but when it's out of balance, the consequences can be profound.

What is Immunoglobulin A (IgA)?

IgA is one of five classes of antibodies (immunoglobulins) your immune system produces. It exists in two subclasses: IgA1 (predominant in blood) and IgA2 (predominant in secretions such as saliva, breast milk, and intestinal fluid). Its primary job is to neutralise pathogens before they breach the body's mucosal barriers. In my clinical practice, I often explain to patients that IgA is like the security guard at the entrance of your digestive and respiratory systems.

Why Would Your Doctor Order an IgA Test?

Your physician may measure IgA to investigate:

• Recurrent infections – particularly of the sinuses, lungs, and gut
• Suspected selective IgA deficiency – the most common primary immunodeficiency
• Autoimmune disease workup – such as rheumatoid arthritis, lupus, or celiac disease
• Monitoring multiple myeloma or other monoclonal gammopathies – where a single type of antibody is overproduced
• Liver disease – since the liver produces the secretory component of IgA
• Chronic inflammatory conditions – like inflammatory bowel disease or vasculitis

Normal Reference Ranges for Immunoglobulin A (IgA)

Reference ranges can vary slightly between laboratories, but the following values are typical for healthy individuals. I always tell my patients that these numbers are a guide, not an absolute rule – clinical context is everything.

Note: IgA levels in children are lower at birth and gradually rise to adult levels by adolescence. In elderly individuals, a slight upward shift is common but not always clinically significant.

What Does a Low IgA Level Mean?

A persistently low IgA is most often due to selective IgA deficiency, which affects about 1 in 600 individuals. Many people with this condition have no symptoms, but others experience recurrent respiratory tract infections, allergies, autoimmune disorders, and a higher risk of anaphylactic reactions to blood transfusions. In my experience, the first clue is often a history of frequent ear infections or sinusitis that doesn't quite fit the usual pattern.

Is Low IgA Dangerous?

It depends. Many individuals with low IgA live completely normal lives. However, if you also have low IgG or low total immunoglobulins, or if you're having recurrent serious infections, you may need further evaluation by a clinical immunologist. At your next visit, I would also check for associated conditions such as celiac disease and systemic lupus erythematosus.

What Does a High IgA Level Mean?

Elevated IgA can indicate chronic inflammation, liver disease (especially alcoholic cirrhosis), autoimmune conditions such as rheumatoid arthritis or IgA vasculitis (Henoch–Schönlein purpura), and certain monoclonal gammopathies including multiple myeloma. In my patients with longstanding rheumatoid arthritis, I often see moderately raised IgA along with other acute-phase reactants.

Is High IgA Dangerous?

A mild elevation may be benign, especially if you have an active infection or inflammation. But a very high level – say, over 500 mg/dL – warrants a closer look. In multiple myeloma, the IgA paraprotein can cause kidney damage and hyperviscosity syndrome. I always advise follow-up with serum protein electrophoresis (SPEP) and immunofixation if an isolated IgA spike is suspected.

IgA During Pregnancy

Pregnancy naturally modulates the immune system. IgA levels often decrease slightly during gestation due to haemodilution and hormonal changes. After delivery, levels usually return to pre-pregnancy baselines within a few weeks.

How Pregnancy Affects IgA Levels

If you have known IgA deficiency and are pregnant or planning to conceive, it's important to discuss this with your obstetrician. Selective IgA deficiency is associated with a slightly increased risk of miscarriage and autoimmune disease flare-ups, but with careful monitoring, most women have healthy pregnancies.

IgA and Celiac Disease

The tissue transglutaminase IgA (tTG-IgA) test is the gold standard screening for coeliac disease. However, if you have low total IgA, the tTG-IgA test can be falsely negative. That's why many labs automatically measure total IgA when ordering celiac serology. If your total IgA is low, we rely on the IgG-based tests instead.

Factors That Can Affect Your IgA Result

Several factors can temporarily alter IgA levels:

• Medications: Phenytoin, valproic acid, and some immunosuppressants can lower IgA.
• Infection or vaccination: Acute infection may transiently raise IgA.
• Chronic liver disease: Cirrhosis can markedly increase IgA.
• Age: Levels climb during childhood and then stabilise in adulthood.

When to Speak with Your Doctor

If your IgA result is outside the normal reference range, don't jump to conclusions. Many people with abnormal levels have no symptoms at all. The key is to look at the whole picture – your symptoms, family history, and other lab values. In my practice, I schedule a follow-up discussion to review the results and decide whether additional testing or a referral to a specialist is needed.

Note on LOINC coding: The standard LOINC code for serum Immunoglobulin A (IgA) measurement is 2454-7 (IgA, serum).