X-Linked Immunoglobulin Marker
Overview
X-Linked Immunoglobulin Marker typically refers to IgM or related immunoglobulin levels measured in the context of X-linked agammaglobulinemia (XLA), a primary immunodeficiency caused by BTK gene mutations. IgM is a pentameric antibody produced by B cells that provides early immune defense against pathogens through complement activation and agglutination. Low or absent IgM levels indicate severe B cell dysfunction characteristic of XLA, while normal or elevated levels help rule out this condition. Clinically, IgM measurement is essential for diagnosing XLA, monitoring Bruton's tyrosine kinase (BTK) deficiency, and guiding immunoglobulin replacement therapy.
Clinical Use Cases
- Diagnosis of X-linked agammag lobulinemia (XLA) or Bruton's agammaglobulinemia.
- Screening for primary B-cell immunodeficiencies in males with recurrent bacterial infections.
- Monitoring response to intravenous immunoglobulin (IVIG) replacement therapy.
- Genetic counseling and family screening for BTK mutations.
- Differentiating XLA from other hypogammaglobulinemias or common variable immunodeficiency.
Specimen Types
- Serum.
- Plasma (less common).
Measurement Methods
- Nephelometry or turbidimetry for quantitative IgM levels.
- Radial immunodiffusion.
- Enzyme-linked immunosorbent assay (ELISA).
- Flow cytometry for B cell enumeration alongside immunoglobulin levels.
- Genetic testing of BTK gene for confirmation.
Test Preparation and Influencing Factors
- No fasting required.
- Recent IVIG infusion elevates measured IgM levels.
- Acute infections may transiently increase polyclonal IgM.
- Sample hemolysis interferes with nephelometric assays.
- Age-dependent reference ranges; neonatal levels naturally low.
- Liver disease or monoclonal gammopathies affect results.
Synonyms
- Bruton's agammaglobulinemia marker.
- IgM (in XLA context).
- BTK deficiency immunoglobulin profile.