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Antibodies or immunoglobulins (Ig) are formed by plasma cells as a humoral immune response to antigens. The first antibodies formed after antigen stimulation are of the IgM class, followed later by IgG and also IgA antibodies. IgD normally occurs in serum in trace amounts.
Increased serum immunoglobulin concentrations occur due to polyclonal or oligoclonal immunoglobulin proliferation in hepatic diseases (chronic hepatitis, liver cirrhosis), acute and chronic infections, autoimmune diseases, as well as in the cord blood of neonates with intrauterine and perinatal infections. Increases in serum immunoglobulin concentration are seen in monoclonal gammopathies such as multiple myeloma, Waldenstrom's macroglobulinemia, primary amyloidosis, and monoclonal gammopathy of undetermined significance.
Decreased serum immunoglobulin concentrations occur in primary immunodeficiency conditions as well as in secondary immune insufficiencies including advanced monoclonal gammopathies, lymphatic leukemia, and advanced malignant tumors.
Quantitative determination of the immunoglobulins can provide important information on the humoral immune status.
Changes in IgD concentration are used as a marker of changes in the size of the clone of monoclonal IgD plasma cells.
The physiologic significance of serum IgD concentration is unclear and in many normal persons serum IgD is undetectable.
Increased concentrations may be due to polyclonal (reactive) or monoclonal plasma cell proliferative processes.
A monoclonal IgD protein is present in 1% of patients with myeloma. Monoclonal IgD proteins are often in low concentrations and do not have a quantifiable M-peak on serum protein electrophoresis. However, the presence of an IgD monoclonal protein is almost always indicative of a malignant plasma cell disorder such as multiple myeloma or primary amyloidosis.
An elevated IgD cannot be taken as evidence for a monoclonal IgD protein. MPSS / Monoclonal Protein Studies, Serum should be performed to distinguish between a polyclonal and monoclonal IgD.
< or =10 mg/dL
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3. Tietz NW: In Clinical Guide to Laboratory Tests. Second edition. Philadelphia, WB Saunders Company, 1990, p 325