Immunoglobulin D (IgD) is found in very small quantities in the blood and is one of the least understood immunoglobulin classes. It is expressed predominantly on the surface of mature B lymphocytes, where it acts as an antigen receptor alongside IgM, playing a role in B cell activation and maturation.
Clinical measurement of serum IgD is less common than other immunoglobulins. Elevated IgD is associated with IgD myeloma (a rare subtype of plasma cell dyscrasia), periodic fever syndromes (particularly Hyper-IgD syndrome, caused by mevalonate kinase deficiency), and certain chronic infections. Measuring IgD alongside other immunoglobulins helps provide a complete immunological picture.
FAQs
What is Hyper-IgD syndrome?
Hyper-IgD syndrome (mevalonate kinase deficiency) is an autoinflammatory periodic fever syndrome caused by mutations in the MVK gene encoding mevalonate kinase. It causes recurrent fever episodes lasting 3-7 days with lymphadenopathy, abdominal pain, rash, and elevated IgD. Genetic testing is the definitive diagnostic test.
Is IgD deficiency a problem?
IgD deficiency is not a recognised clinical immunodeficiency condition. Unlike IgA deficiency, there is no evidence that low or absent IgD causes clinical immune problems.
How rare is IgD myeloma?
IgD myeloma accounts for approximately 1-2% of all myeloma cases and is considered rare. It can be clinically aggressive and is often associated with Bence Jones proteinuria (light chain excretion in urine) and renal impairment. Diagnosis may be delayed if IgD is not included in the myeloma screening panel.
Is IgD routinely measured?
IgD is not part of standard immunoglobulin panels in most laboratories. It is specifically ordered when IgD myeloma or Hyper-IgD syndrome is suspected, or as part of comprehensive immunoglobulin profiling in specialist settings.
