IgA

Antibodies come in five kinds, and IgA is the kind your body sends outward. It is made by immune cells just beneath your mucous membranes and secreted into the layer of mucus on your gut wall, in your airways, in saliva, tears and breast milk. There it intercepts bacteria and viruses before they enter your tissue: a border guard, where IgG in the blood is the domestic police. Some IgA also circulates in the blood, and that part is what this test measures. It is a sum of all your IgA, regardless of what it is directed against; that is different from an IgA antibody against one target, such as the coeliac test, which measures IgA against a gut enzyme and has its own numbers. Your report shows IgA in g/L. Normal for an adult is 0.7 to 3.5 g/L, where the labs overlap; the range still rises in the teenage years and differs slightly per lab at both ends.

IgA is measured for two reasons, and the first is the coeliac test. That test measures an IgA antibody, and anyone who makes little or no IgA themselves always tests negative on it, even with coeliac disease. That is why total IgA belongs as standard beside the coeliac test: it says whether the test could measure anything at all. An IgA deficiency occurs in about one in six hundred people, and precisely those people have an increased chance of coeliac disease. The second reason is the immune system itself. An IgA deficiency is the most common inborn immune deficiency, and most people notice nothing of it; some have more frequent airway and gut infections, allergies or autoimmune diseases. Anyone who keeps catching colds or getting sinus infections often has IgA determined together with IgG and IgM to see whether the immune system is complete. A high IgA has little to do with the immune system and a lot with lasting stimulation. Alcohol is the best-known cause: the liver clears IgA, and with heavy drinking and with a fatty or diseased liver it accumulates. Chronic infections and inflammations, of the gut, the airways or the gums, do the same. For anyone who wants to stay healthy a high IgA is therefore more often a question about alcohol and the liver than about the immune system.

A high IgA comes, in order of how often it occurs, from: plenty of alcohol and a fatty or diseased liver, a lasting infection or inflammation of gut, airways or gums, autoimmune diseases such as rheumatoid arthritis, and rarely a kidney disease based on IgA or a proliferation of the cells that make IgA. With a high value the liver values and your alcohol use are the first look, and an inflammation you know of the second. A low IgA is usually inborn and harmless: an IgA deficiency you notice nothing of, which does mean the coeliac test needs a different approach in you. Some people with a deficiency have more frequent infections or allergies. More rarely a low IgA is acquired: from medicines that suppress the immune system, from protein loss through the kidneys or the gut, or as part of a broader immune deficiency in which IgG is low too. Read IgA beside IgG and IgM, the other two large antibody classes, beside the liver values with a high value, and always beside the coeliac test if that was done.