IgD stands for immunoglobulin D, one of the classes of immunoglobulins (also called antibodies) that are in the blood. IgD is mainly found on the surface of B-cells and may help regulate B-cell function. The role of IgD in the immune system is not well understood.
The 'low', 'normal' and 'high' ranges vary with age, and are also lab-specific. However, a reasonable normal range is 0.3-3.0mg/dl.
A high level of IgD may indicate IgD multiple myeloma. IgD multiple myeloma is much less common than IgA or IgG multiple myeloma.