Doctors measure the amount of immunity-imparting proteins in the human body with a blood test called quantitative nephelometry. Specifically, the exam detects the levels for three distinct immunoglobulins, or antibodies, commonly referred to by the letters IgA, IgG and IgM. When deficiencies or surpluses are noted for any of the three quantitative immunoglobulin levels, it could indicate any number of conditions or diseases.
A functioning immune system will naturally produce the amount of antibodies needed to combat most of the antigens encountered by the body throughout life, from bacterial infections and cancers to toxic substances and other foreign matter. Many conditions or diseases can counter this system, though, like Autoimmune Immunodeficiency Syndrome (AIDS), lupus, multiple sclerosis, chronic thyroid disease and even arthritis. These are some of the conditions that a quantitative immunoglobulin test seek to identify.
When a quantitative immunoglobuliin test reveals normal results, it means that all three antibodies are present at prescribed levels. That means IgA is between 100 and 400 mg/dL, IgG is 560 to 1,800 mg/dL and IgM is 45 to 250 mg/dL. This indicates that the body is likely to be deploying the correct matrix of antibodies to defend itself in a healthy way. When patients have levels above or below any of the three ranges, a key step has been taken in helping a clinician determine whether they have a disorder in need of treatment.
When IgA levels are too high or too low, it could result in digestive problems. An infection, irritable bowel syndrome, myeloma or any other disease in the digestive tract are potential suspects. The other two antibody measures, by contrast, mean different things depending on whether the level is too high or too low.
With IgG, low levels on a quantitative immunoglobulin exam could mean leukemia, myeloma and preeclampsia. Increases in IgG, though, could mean the onset of other serious conditions like an infection, liver disease or chronic arthritis. High and low levels of IgM, similarly, point toward different conditions: lymphona, arthritis or monomucleosis if high; leukemia, myeloma and other rarer conditions if low.
Since some conditions show up with decreases or increases in more than one antibody that is measured with the quantitative immunoglobulin test, doctors and lab technicians examine each level individually and as a group to make more certain diagnoses. In many cases, patients are administered the quantitative immunoglobulin test when suffering from a chronic infection. This may lead a physician to suspect the patient is suffering from some condition that is compromising the immune system.