Immunoglobulin D (IgD) is the least abundant of the five major antibody classes in human blood. Most IgD is found on the surface of B lymphocytes, where it plays a role in initiating immune responses. Circulating serum IgD is present in very small quantities and has limited clinical application outside of specific specialist contexts.
The primary clinical use for IgD measurement is in the investigation of hyper-IgD syndrome (HIDS), now more accurately called mevalonate kinase deficiency. This is a rare hereditary autoinflammatory condition caused by mutations in the MVK gene, typically presenting in infancy or early childhood with recurrent episodes of fever, lymphadenopathy, abdominal pain, and joint inflammation. Episodes tend to recur every four to eight weeks, and an elevated IgD level between or during attacks supports the clinical suspicion.
It is worth noting that a normal IgD result does not rule out HIDS. Some confirmed cases have normal or borderline IgD levels, particularly between attacks or as the patient ages. Definitive diagnosis requires MVK genetic testing, not IgD measurement alone. Mildly elevated IgD can also occur in other chronic inflammatory and infectious conditions without any connection to HIDS.
This test is rarely ordered outside specialist immunology, rheumatology, or paediatric settings. If your specialist has requested this test, it is likely part of a broader investigation into recurrent fevers or an autoinflammatory syndrome. The result will be interpreted in the context of your clinical presentation, family history, and other investigations.
To investigate suspected hyper-IgD syndrome (HIDS/mevalonate kinase deficiency) in the context of recurrent periodic fevers, and as part of a comprehensive immunoglobulin panel in immunology assessments.
