Immunoglobulin A (IgA) Blood Test: Total IgA Explained

Immunoglobulins are proteins made by the immune system. IgA is present in blood and in secretions such as saliva and tears. It helps protect mucosal surfaces, including the airways and digestive tract. A serum IgA result describes the blood sample, not the amount of IgA at every surface in the body.^{See reference 1}

Clinicians may request quantitative immunoglobulins when investigating recurrent infections or possible immune-system disorders. IgA may be measured with IgG and IgM. Symptoms, medical history and the pattern across the different immunoglobulins matter more than an isolated flag.^{See reference 1}

IgA reference intervals vary with age. Mayo Clinic Laboratories, for example, reports separate age bands for its serum assay. The interval printed by the laboratory that performed your test is the relevant comparison; an adult interval should not be applied to a child.^{See reference 2}

Methods and manufacturers can give results that are not directly comparable. When following a trend, keep the reporting laboratory, method if supplied, unit, date and age-appropriate interval together. Converting a unit does not remove a difference between assays.^{See reference 2}

The exact unit relationship is 1 mg/dL = 0.01 g/L: one gram is 1,000 milligrams, and one litre is 10 decilitres. Divide a value in mg/dL by 100 to express it in g/L; multiply g/L by 100 to express it in mg/dL. This changes the unit only.

For an invented unit example, 200 mg/dL and 2.00 g/L are the same concentration. The example does not establish a normal, low or high IgA level. Convert the matching reference interval too before making a numerical comparison.

Low serum IgA can occur in primary or secondary immune deficiency. “Selective IgA deficiency” refers to a pattern involving deficient IgA with other immunoglobulins preserved, rather than every slightly low result. Diagnosis needs the broader blood-test and clinical assessment.^{See reference 2,See reference 3}

Many people with selective IgA deficiency appear healthy or have mild illness; others have recurrent infections, allergies or autoimmune problems. A concentration alone does not predict which pattern applies. A confirmed IgA deficiency should also be part of the medical history shared with the team arranging a blood transfusion, because some blood products can cause reactions in affected people.^{See reference 3}

IgA can rise in liver disease, connective-tissue disorders or infection. It can also be increased in conditions involving an abnormal population of antibody-producing cells. Measuring total IgA alone cannot distinguish a broad antibody rise from one produced by a single cell population; clinicians may use protein electrophoresis and other tests for that question.^{See reference 2}

A high number is not evidence that immunity is stronger, and it does not identify a specific disease. Read it as one part of the investigation rather than selecting a cause from an online list.^{See reference 1,See reference 2}

IgA deficiency can make IgA-based celiac antibody tests less reliable. Total IgA helps establish that context, and clinicians may use IgG-based tests when IgA is deficient. A normal total IgA does not itself test for celiac disease; it answers a different question from tTG-IgA.^{See reference 4}