2 These may occur as an isolated defect or as part of a wider combined immunodeficiency affecting both T- and B-cells. There are many types of antibody deficiencies ranging from isolated IgA deficiency to severe deficiencies of all immunoglobulins. Patients with antibody deficiency are particularly predisposed to recurrent sinopulmonary infections, especially with polysaccharide encapsulated organisms including Streptococcus pneumoniae and Haemophilus influenzae.
The tests should be ordered if a patient has symptoms suggestive of an immunoglobulin deficiency, such as family history of immunodeficiency, recurrent or severe or unusual bacterial infections, lack of response to antibiotics, unusual or recurrent viral infections and/or chronic unexplained diarrhoea. A low level of immunoglobulin is termed ‘hypogammaglobulinaemia’. Serum immunoglobulin tests are used for the evaluation of antibody (humoral) immunodeficiencies. IgD and IgE will not be discussed in this article. Some conditions cause excess levels, some cause deficiencies, and others cause a combination of increased and decreased levels. Testing is used to help diagnose various conditions and diseases that affect the levels of one or more of these immunoglobulin classes. Quantitative serum immunoglobulin tests are used to detect abnormal levels of the three major classes (IgG, IgA and IgM). In normal serum, about 80% is IgG, 15% is IgA, 5% is IgM, 0.2% is IgD and a trace is IgE. There are five classes of immunoglobulin (Ig): IgG, IgM, IgA, IgD and IgE. They contain antibody activity and are produced by the terminal cells of B-cell differentiation known as ‘plasma cells’. It considers areas such as indications, what to tell the patient, what the test can and cannot tell you, and interpretation of results.
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This article forms part of our ‘Tests and results’ series for 2013, which aims to provide information about common tests that general practitioners order regularly.
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